Bingham University Karu General Chemistry CHM 102 Notes 2024 PDF

BINGHAM UNIVERSITY KARU DEPARTMENT OF CHEMICAL SCIENCES/ SECOND SEMESTER 2023/2024 SESSION/ COURSE: GENERAL CHEMISTRY CHM 102 COURSE LECTURER: DR ISHEGBE JOYCE MEANING OF ORGANIC CHEMISTRY: Organic chemistry is one of the most important disciplines of science...

BINGHAM UNIVERSITY KARU DEPARTMENT OF CHEMICAL SCIENCES/ SECOND SEMESTER 2023/2024 SESSION/ COURSE: GENERAL CHEMISTRY CHM 102 COURSE LECTURER: DR ISHEGBE JOYCE MEANING OF ORGANIC CHEMISTRY: Organic chemistry is one of the most important disciplines of science which deals with the study of carbon compounds especially hydrocarbons and their derivatives. Organic chemistry is the branch of chemistry that deals with a specific sector of compounds found in nature and manufactured synthetically. It is the science that studies the organic compounds and molecules. Some of these include biomolecules, plastics, petroleum products, and more. Organic chemistry is a branch of chemistry that deals with the structure, characteristics, and reactions of organic molecules and organic materials, which are any forms of matter that contain carbon atoms. Their analysis of structure yields their structural formula. The study of properties includes both physical and chemical qualities as well as the assessment of chemical reactivity to understand their behaviour. Examples of organic reaction research include studying individual organic compounds in the lab and conceptually (in silico), as well as the chemical synthesis of pharmaceuticals, natural products, and polymers. IMPORTANCE OF ORGANIC CHEMISTRY 1. Organic substances are everywhere around us. Many contemporary materials contain organic chemicals, at least in part. They are crucial to the development of the economy, as well as to biochemistry, biotechnology, and medicine. 2. Organic compounds can be found in a variety of products, including agrichemicals, coatings, cosmetics, detergent, dyes, food, fuel, petrochemicals, pharmaceuticals, plastics, and rubber. Among the substances investigated in organic chemistry are hydrocarbons (molecules made only of carbon and hydrogen) and carbon-based compounds that also contain other elements, including oxygen, nitrogen, sulphur, phosphorus (present in many bio-chemicals), and halogens 3. Organic chemistry plays an important part in our daily life because food, clothes, paper, ink, rubber, soap, perfumes, medicines etc. are indispensable to us for proper living. 4.Organic compounds are important constituents of many products e.g., paint, food, plastic, explosive, medicine, petrochemical, pesticide etc. Further, the study of organic chemistry is important for chemists and pharmacists in order to synthesize medicines for the alleviation of human suffering. 5. Heterocyclic compounds are one of the most important classes of compounds which are of great importance in pharmaceutics because of their specific chemical reactivity. Nitrogen containing heterocycles are structural constituent of a variety of active pharmaceuticals, biologically active natural and non-natural compounds. Importance of Organic Chemistry Organic chemistry is significant because it is the study of life and all of its chemical reactions. Doctors, veterinarians, dentists, pharmacologists, chemical engineers, and chemists are among the professionals who apply the understanding of organic chemistry. The relevance of organic chemistry may be seen in the huge array of substances we utilize on a daily basis. Some common uses of Organic compounds are- 1. Food: Carbohydrates, proteins, and fats are the carbon compounds that form the basis of food materials. Vitamins are also organic in nature. 2. Cleansing agents: Organic solvents are frequently used in industries and laboratories to remove contaminants. For example, in the extraction of drugs from plants, petroleum ether is used to separate the fatty materials from the pulp. As a result of organic chemistry’s knowledge of polarity, solubility, and partition factors, solvents are used to separate components for better use. 3. Sterilizing agents:- The majority of sterilizing and disinfecting agents, such as phenol and formaldehyde, are carbon compounds. They can kill microorganisms and even human body cells due to their characteristics such as solubility and pH. These destroy bacteria and other germs by dissolving the cell wall or damaging the protein layer, among other things.  4. Analytic substances:- The majority of the substances we use, such as medications and insecticides, are tested qualitatively and quantitatively using various titrations, chromatography methods, and spectrophotometry. In this case, the reagents used, such as acids or bases or reductive oxidative species, are organic in nature. Furthermore, organic chemistry is responsible for the development of endpoint indicators in titration. 5. Valuables:- Carbon compounds, interestingly, are proven to be very precious, durable, and toughest in the world. Diamond and graphite are both carbon-only compounds that contain no other elements. They’re both widely used and expensive. Petroleum is the world’s other most valuable resource for meeting global fuel demands. These petroleum products are further diversified for a variety of applications. Importance of Heterocyclic Compounds Applications of Aromatic Heterocycles in Agriculture-Pests such as rodents, insects, germs, and weeds consume or destroy the majority of the food meant for humans. Biological plant protection techniques have a lot of potential, but chemical control is still the most prevalent way. Pesticides, which include herbicides (weed killers), insecticides, fungicides, and rodenticides, are used to control pests by chemical means. Plant growth stimulators and regulators are also quite important. Because heterocyclic chemicals are involved in so many biological systems, it’s no surprise that they make up the bulk of pesticides. Fluorescence – Fluorescence is defined as the absorption of radiation by atoms or molecules, followed by the immediate emission of electromagnetic radiation when the particles move to lower energy states. Fluorescent heterocyclic compounds have an important role in a variety of fields, including emitters for electroluminescence devices. Pharma – Heterocycles are common fragments of the great majority of commercially available medicines, and they serve an important role in modern drug synthesis. Common usage of Heterocyclic compounds is found in Antimalarial medicines, Anti-Inflammatory medicines FULLERENE(ALLOTROPE/POLYMORPH OF CARBON) An allotrope is one or more forms of a chemical element that can exist in the same physical state. Allotropism is the ability of an element to exist in multiple forms. Well-known allotropes of carbon include diamond and graphite/graphene, amorphous carbon, C70 fullerene, C60 buckminsterfullerene, C540 fullerene, and Ionsdaleite. Fullerene is nothing but an allotrope of carbon wherein its molecules consist of carbon atoms that are connected by single and double bonds. This results in the formation of a closed or partially closed cage-like structure (a mesh consisting of fused rings) that further contain several atoms. The fullerene molecule in this form can either have a hollow sphere, be it an ellipsoid, a tube, or it can also have many other different shapes and sizes. When the carbon molecules are arranged in a cylindrical form they usually form a tube-like structure known as carbon nanotubes. Structure of Fullerene Fullerenes in their natural form tend to be highly symmetrical. Their structure is quite similar to that of graphite and is made up of a sheet of connected hexagonal rings (cage structure). However, they have pentagonal and sometimes heptagonal rings which do not allow the sheet to become planar. They are often referred to as buckyballs and buckytubes depending on their shape. Cylindrical fullerenes are referred to as nanotubes. Buckyballs and carbon nanotubes have been used as building blocks for a great variety of derivatives and larger structures. Uses of fullerene i. Fullerenes are used in the medical field as light-activated antimicrobial agents. ii. It is also used in several biomedical applications including the design of high-performance MRI contrast agents, X-ray imaging contrast agents, photodynamic therapy and drug and gene delivery. iii. Buckminsterfullerene is used in drug delivery systems, in lubricants and as a catalyst. iv. It is also used as a conductor. v. Some types of fullerene can be used as an absorbent for gases. vi. It is used in making cosmetic products. vii. C60 based films are used for photovoltaic applications. Fullerenes are used in making carbon nanotubes-based fabrics and fibres. ISOLATION AND PURIFICATION OF ORGANIC COMPOUNDS The purification of organic compounds is necessary, though a complex step after its extraction from a natural source or synthesis in the laboratory. The method of purification of the organic compound depends mainly on the nature of the compound and the impurities present.) One easy method to check the purity of an organic compound is to either melt or boil it, as organic compounds tend to have sharp melting and boiling points. Purification means the removal of unwanted impurities present in an organic compound. The general methods of purification are listed below: Methods of Purification a. Sublimation: Some solids can directly pass to the vapour state without going through the liquid phase. The purification technique which exploits this property is called sublimation. It is helpful in separating sublimable compounds from non-sublimable ones. The substance is heated in a China dish above, and an inverted funnel is kept to collect the sublimable compounds. The funnel is kept cool so as to hasten the process. Vapours of the substance solidify on the funnel. b. Crystallisation The principle here is that the compound and the impurities have different solubilities in a solvent. A solvent is chosen, where the compound to be purified is sparingly soluble, that is, it is sparingly soluble at a lower temperature and soluble at a higher temperature. The solution is heated to get a saturated solution, and on cooling, the crystals of the compounds are removed via filtration. For example, crystals of benzoic acid can be crystallised with water. Benzoic acid is sparingly soluble in cold water and soluble in hot water. Purification of Liquids c. Distillation: The underlying principle behind distillation is that the mixture of liquids can be separated by the difference in their boiling points. The boiling point is defined as the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure. This method separates volatile liquids from non-volatile liquids. The setup is given below. The mixture is taken in the RB flask and boiled. The more volatile, i.e., component with a lower boiling point, evaporates faster and is collected in a separate container. A condenser is used to hasten the process of condensation. For example, a mixture of chloroform and aniline can be separated by distillation. The boiling point of chloroform is 60°C, and that of aniline is 189°C. Therefore, distillation can be used to separate a mixture of chloroform and aniline. d. Fractional Distillation This method is employed when the difference between the boiling points of the liquids isn’t much. Since the vapours of such liquids might condense together, a fractionating column is fixed to the mouth of the RB. Vacuum Distillation Since the boiling point is dependent on the atmospheric pressure, the liquids will boil at a temperature lesser than their boiling points if they were distilled in an atmosphere having lower pressure. This is achieved by using a vacuum pump. Since the atmospheric pressure is reduced, the liquids also boil faster, and hence the whole process of distillation is made fast. Steam Distillation In this variant, steam is passed into the flask containing the liquids to be separated. The principle here is that the liquids will boil faster because aqueous tension (vapour pressure of water) helps in equalising the atmospheric pressure. Total pressure = Aqueous tension + vapour pressure of liquid components In the absence of aqueous tension, the process of boiling would have been continued until it equalises the atmospheric pressure. Now, with the addition of steam, this process is expedited. Differential Extraction This method is used for immiscible liquids, that is, liquids that do not mix together. For example, oil and water are immiscible. The immiscible liquids are taken in a separating funnel and left undisturbed. After a while, they separate out according to their specific gravities, with the heavier liquid at the bottom. Then, they are collected later. Substances can also be separated according to their preferential solubilities in the liquid. For example, if phenol is to be extracted, it can be preferentially extracted using NaOH solution as one of the liquids used. Chromatography Chromatography is an important separation technique used to separate constituent particles of a mixture of substances to purify the compounds and check the purity of organic compounds. In this technique, on a stationary phase (solid or liquid), a mixture of substances is applied. The mixture of gas or the pure solvent is allowed to move slowly on the stationary phase. Due to this, the components of the mixture start separating from one another. Chromatography is of two types: Adsorption Chromatography and Partition Chromatography Adsorption Chromatography: It is based on the principle that the constituents are adsorbed on an adsorbent in varying degrees. The adsorbents used are generally silica gel or alumina. When a mobile phase moves over the fixed phase, different constituents of the mixture get adsorbed at various distances over the fixed phase. Adsorption Chromatography is further classified into: Column Chromatography Thin Layer Chromatography Column Chromatography Here, a mixture is separated over a column of either silica gel or alumina, packed in a glass column. The constituent with the most affinity with the fixed phase is adsorbed at the top, and so on. It is then retrieved by using an eluant. The solvent is then evaporated to get the constituent. Thin Layer Chromatography Here, a sheet of alumina is taken (0.2 mm thick), over which a small spot of the mixture is placed, and it is kept in a suitable solvent. The solvent rises due to capillary action, and the constituents also rise with the solvent depending on their differential adsorption, and thereby, they are separated. QUALITATIVE AND QUANTITATIVE ANALYSIS OF ORGANIC COMPOUNDS Some of the most commonly occurring elements in organic compounds are carbon, hydrogen, sulfur, nitrogen and halogen elements. Detection of these elements can be done through qualitative analysis Qualitative analysis is a method used to measure changes in melting point, color, odor, radioactivity, reactivity, bubble production, boiling point and precipitation. On the other hand, quantitative analysis is a method of analysis to determine the number of elements or molecules produced during a chemical reaction. We can therefore highlight that qualitative analysis is a method to analyze the species present in a compound and is more focused on finding the elements and ions present in the given compound whereas quantitative analysis is based on finding the quantity (how much) of elements present in the compound Quantitative analysis is an analysis method used to determine the number of elements or molecules produced during a chemical reaction. Organic compounds comprise carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur and halogens. The various methods used for the measurement of the percentage composition of elements in an organic compound are 1. Detection of C and H C and H are detected by heating the compound with CuO in a dry test tube. They are oxidised to CO2 and H2O, respectively. If the CO2 turns lime water milky, and H2O turns anhydrous CuSO4 blue, then the presence of C and H is confirmed. ii. Test for Phosphorous The organic compound is heated with an oxidising agent to oxidise phosphorous to phosphate. The solution is then boiled with concentrated HNO3 and treated with ammonium molybdate. Yellow precipitate confirms the presence of phosphorous. iii. Estimation of Sulphur A known mass of the compound is heated with conc. HNO3 in the presence of BaCl2 solution in the Carius tube. Sulphur is oxidised to H2SO4 and precipitated as BaSO4. It is then dried and weighed. Percentage of S = ((Atomic mass of S)/(Molecular mass of BaSO4)) x (( Mass of BaSO4)/(Mass of the compound)) x 100 iv. Estimation of Phosphorus A known mass of the compound is heated with HNO3 in a Carius tube, which oxidises phosphorous to phosphoric acid. It is then precipitated as ammonium phosphomolybdate ((NH4)3PO4.12MoO3) by adding NH3 and ammonium molybdate ((NH4)2MoO4). Then, it is filtered, dried and weighed. Iv. Estimation of Nitrogen Estimation of Nitrogen by Dumas Method A known mass of the compound is heated with CuO in an atmosphere of CO2, which yields free nitrogen along with CO2 and H2O. CxHyNz + (2x+ 0.5y) CuO → xCO2 + 0.5y H2O + 0.5z (N2) + (2x+ 0.5y)Cu The gases are passed over a hot copper gauze to convert trace amounts of nitrogen oxides to N2. The gaseous mixture is collected over a solution of KOH, which absorbs CO2, and nitrogen is collected in the upper part of the graduated tube. Nature of Organic molecules 1. Catenation – Catenation can be defined as the self-linking of atoms of an element to form chains and rings. This definition can be extended to include the formation of layers (two-dimensional catenation) and space lattices (three-dimensional catenation). 2. Tetravalency and small size – Carbon exhibits’ tetravalency. The tetravalency of carbon can be satisfied by forming bonds with carbon, hydrogen or other atoms. The carbon atom has 4 electrons in its valence shell. In order to account tetravalency it is believed during the process of bond formation which is energy-releasing process the two electrons in the 2s orbital get unpaired and out of them, one is promoted to empty orbital carbon can also form double bonds by sharing four electrons with a neighboring carbon atom or triple bonds by sharing six electrons with a neighboring carbon atom. carbon with three electron groups attached will be trigonal planar, and carbon with two electron groups attached will be linear. Two carbons can be attached together in single bond, a double bond, or a triple bond. Notice, in each example carbon makes four total bonds. The number of hydrogen atoms in each molecule decreases as the number of carbon–carbon bonds increase. Simple hydrocarbon compounds are nonpolar due to the shape and the small electronegativity difference between carbon and hydrogen atoms. When carbon is bonded to a halogen or oxygen atom, the resulting bond is polar Contrasting Properties and Examples of Organic and Inorganic Compounds Organic Properties Example: Hexane Inorganic Properties Example: NaCl low melting points −95°C high melting points 801°C low boiling points 69°C high boiling points 1,413°C low solubility in insoluble in greater solubility in water; soluble in water; water; high water; soluble in low solubility in nonpolar insoluble in solubility in gasoline solvents gasoline nonpolar solvents Flammable highly flammable Nonflammable Nonflammable aqueous solutions nonconductive aqueous solutions conduct conductive in do not conduct electricity aqueous solution electricity exhibit covalent covalent bonds exhibit ionic bonding ionic bonds bonding Classification of Organic Compounds 1. Acyclic or Open Chain Compounds & Alicyclic or Closed Chain or Ring Compounds – Organic compounds are classified as open-chain compounds and closed chain compounds in terms of the carbon chain. 2. Aromatic Compounds – Plants and micro-organisms have an exclusive route to benzene-ring compounds. The great majority of aromatic compounds in nature, therefore, are produced by plants and microorganisms, and animals are dependent upon plants for many aromatic compounds either directly or Indirectly. 3. Heterocyclic Aromatic Compounds – In the twentieth century it is witnessed that the first inorganic heteroaromatic compound produced in the laboratory. Some of these heterocyclic aromatic compounds are very important in biochemical processes, drugs, and agrochemical 4. Functional groups Functional groups are important in organic chemistry because they may be used to classify structures and predict characteristics. A functional group is a molecular module whose reactivity is expected to be the same in a variety of molecules, within certain limits. The chemical and physical characteristics of organic compounds can be significantly influenced by functional groups. Functional groupings are used to classify molecules. Aliphatic compounds According to their saturation state, aliphatic hydrocarbons are grouped into three types of homologous series: alkanes, alkenes, and alkynes. The rest of the group is divided according to functional groups present. Straight-chain, branched-chain, and cyclic compounds are all examples of such compounds. In petroleum chemistry, features like the octane number or cetane number are affected by the degree of branching. Aromatic compounds Conjugated double bonds are found in aromatic hydrocarbons. This indicates that every carbon atom in the ring is sp2 hybridized, which increases the ring’s stability. The most famous example is benzene, whose structure was suggested by Kekulé, who was the first to propose the delocalization or resonance principle to explain it. Heterocyclic compounds The features of the cyclic hydrocarbons are again altered if heteroatoms are present, which can exist as either substituents connected externally to the ring (exocyclic) or as a member of the ring itself (endocyclic). In the latter situation, the ring is referred to as a heterocycle. Oxygen, sulfur, or nitrogen are the most prevalent heteroatoms in heterocyclic molecules, with the latter being particularly abundant in biological systems. Heterocycles can be found in a variety of items, including aniline dyes and drugs. They’re also found in a variety of biochemical compounds like alkaloids, vitamins, steroids, and nucleic acids. Homologous series Homologous series is a series of compounds with similar chemical properties and some functional groups differing from the successive member by CH2. Carbon chains of varying lengths have been observed in organic compounds having the same general formula. Such organic compounds that vary from one another by a repeating unit and have the same general formula form a series of compounds. Alkanes with general formula CnH2n+2, alkenes with general formula CnH2n and alkynes with general formula CnH2n-2 form the most basic homologous series in organic chemistry. Examples of Homologous series The successive members vary from each other by a CH2 unit. For example in CH4 and C2H6, the difference is -CH2 unit and the difference between C2H6 and C3H8 is also -CH2 unit. So CH4, C2H6, and C3H8 are homologs. The same thing can be observed in the case of alkenes in which the first member is ethene and the successive members are C3H6, C4H8, and C5H10. They differ from each other by a –CH2 unit. The Alkene formula is written as CnH2n. All the members belonging to this series have the same functional groups. They have similar physical properties that follow a fixed gradation with increasing mass. The properties of CH3OH, C2H5OH, and C3H7OH are similar and follow a gradual change with increasing molecular mass of the successive members of the series. This is because, with the increase in the molecular mass of the compounds, the number of bonds also increases. Therefore, properties such as melting and boiling point, solubility, etc. that depend on the mass and the total number of bonds in a compound show a gradual change with an increase in molecular masses of the compounds. The Chemical properties of the members of a homologous series are the same due to the fact that they all have the same functional groups in them. Structures and Names of Alkanes The simplest organic compounds are composed of carbon and hydrogen atoms only. As we know, there are several different kinds of hydrocarbons. They are distinguished by the types of bonding between carbon atoms and the properties that result from that bonding. Hydrocarbons with only carbon-to-carbon single bonds (C–C) and existing as a continuous chain of carbon atoms also bonded to hydrogen atoms are called alkanes (or saturated hydrocarbons). Saturated, in this case, means that each carbon atom is bonded to four other atoms (hydrogen or carbon)—the most possible; there are no double or triple bonds in the molecules. The three simplest alkanes—methane (CH4), ethane (C2H6), and propane (C3H8)—are shown in Figure 1.1 "The Three Simplest Alkanes". The flat representations shown do not accurately portray bond angles or molecular geometry. Methane has a tetrahedral shape that chemists often portray with wedges indicating bonds coming out toward you and dashed lines indicating bonds that go back away from you. An ordinary solid line indicates a bond in the plane of the page. Figure 1.1 The Three Simplest Alkanes The VSEPR theory correctly predicts a tetrahedral shape for the methane molecule (Figure 1.2 "The Tetrahedral Methane Molecule"). Figure 1.2 The Tetrahedral Methane Molecule Methane (CH4), ethane (C2H6), and propane (C3H8) are the beginning of a series of compounds in which any two members in a sequence differ by one carbon atom and two hydrogen atoms—namely, a CH2 unit. The first 10 members of this series are given in Table 1.2 "The First 10 Straight-Chain Alkanes". Table 1.2 The First 10 Straight-Chain Alkanes Molecular Number of Name Formula Condensed Structural Formula Possible (CnH2n + 2) Isomers Methan CH4 CH4 — e ethane C2H6 CH3CH3 — propane C3H8 CH3CH2CH3 — butane C4H10 CH3CH2CH2CH3 2 pentane C5H12 CH3CH2CH2CH2CH3 3 hexane C6H14 CH3CH2CH2CH2CH2CH3 5 heptane C7H16 CH3CH2CH2CH2CH2CH2CH3 9 octane C8H18 CH3CH2CH2CH2CH2CH2CH2CH3 18 nonane C9H20 CH3CH2CH2CH2CH2CH2CH2CH2CH3 35 decane C10H22 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 75 Consider the series in Figure 1.3 "Members of a Homologous Series". The sequence starts with C3H8, and a CH2 unit is added in each step moving up the series. Any family of compounds in which adjacent members differ from each other by a definite factor (here a CH2 group) is called a homologous series. The members of such a series, called homologs, have properties that vary in a regular and predictable manner. The principle of homology gives organization to organic chemistry in much the same way that the periodic table gives organization to inorganic chemistry. Instead of a bewildering array of individual carbon compounds, we can study a few members of a homologous series and from them deduce some of the properties of other compounds in the series. Figure 1. Members of a Homologous Series Each succeeding formula incorporates one carbon atom and two hydrogen atoms more than the previous formula. The principle of homology allows us to write a general formula for alkanes: CnH2n + 2. Using this formula, we can write a molecular formula for any alkane with a given number of carbon atoms. For example, an alkane with eight carbon atoms has the molecular formula C8H(2 × 8) + 2 = C8H18. Physical properties of alkanes -Alkanes are referred to as saturated hydrocarbons, that is, hydrocarbons having all carbon atoms bonded to other carbon atoms or hydrogen atoms with sigma bonds only. -As the alkanes posses weak Van Der Waals forces, the first four members, C1 to C4 are gases, C5 to C17 are liquids and those containing 18 carbon atoms or more are solids at 298 K. -They are colourless and odourless. -Solubility of Alkanes Due to very little difference in electronegativity between carbon and hydrogen and the covalent nature of C-C bond or C-H bond, alkanes are generally non-polar molecules. polar molecules are soluble in polar solvents whereas non-polar molecules are soluble in non-polar solvents. Hence, alkanes are hydrophobic in nature, that is, alkanes are insoluble in water. However, they are soluble in organic solvents as the energy required to overcome the existing Van Der Waals forces and the energy required to generate new Van Der Waals forces is quite comparable. - Boiling Point of Alkanes As the intermolecular Van Der Waals forces increase with the increase of the molecular size or the surface area of the molecule we observe, The boiling point of alkanes increases with increasing molecular weight. The straight-chain alkanes are observed to have a higher boiling point in comparison to their structural isomers. - Melting Point of Alkanes The melting point of alkanes follows the same trend as their boiling point, that is, it increases with an increase in molecular weight. This is attributed to the fact that higher alkanes are solids and it’s difficult to overcome intermolecular forces of attraction between them. Chemical Properties of Alkanes Alkanes are the least reactive type of organic compound. Alkanes are not absolutely unreactive. Two important reactions that they undergo are combustion, which is the reaction with oxygen and halogenation, which is the reaction with halogens.1. Combustion A combustion reaction is a chemical reaction between a substance and oxygen that proceeds with the evolution of heat and light. Alkanes readily undergo combustion reactions when ignited. When sufficient oxygen is present to support total combustion then carbon dioxide and water are formed. CH4 + 2O2 → CO2 + 2H2O + energy 2C6H14 + 19O2 → 12CO2 + 14H2O + energy The exothermic nature of alkane combustion reactions explains the extensive use of alkanes as fuels. Natural gas which is used in home heating is predominantly methane. 2. Halogenation Halogenation of an alkane produces a hydrocarbon derivative in which one or more halogen atoms have been substituted for hydrogen atoms. An example of an alkane halogenation reaction is CH3-CH3 + Br2 → CH3-CH2-Br + HBr Alkane halogenation is an example of a substitution reaction, a type of reaction that often occurs in organic chemistry. A general equation for the substitution of a single halogen atom for one of the hydrogen atoms of an alkane is R-H + X2 → R-X + H-X PHYSICAL AND CHEMICAL PROPERTIES OF ALKENE Alkenes contain a carbon-carbon double bond which changes the physical properties of alkenes. Alkenes are unsaturated carbon compounds which have a general formula of CnH2n. These compounds are also known as olefins. Alkenes are a family of compounds containing hydrogen and carbon only (hydrocarbons) with a carbon-carbon double bond. Ethene and Propene are the first two hydrocarbons. 1. Physical State -These double-bonded compounds are colourless and odourless in nature. -However, ethene is an exception because it is a colourless gas with a faintly sweet odour. -The first three members of the alkene group are gaseous in nature, the next fourteen members are liquids and the remaining alkenes are solids. 2. Solubility -The alkenes are insoluble in water due to their nonpolar characteristics. -But are completely soluble in nonpolar solvents such as benzene, ligroin, etc. 3. Boiling Point -The boiling points of the compounds increase as the number of carbon atoms in the compound increases. -When alkenes are compared with alkanes, it is found that the boiling points of both are almost similar, as if the compounds are made up of the same carbon skeleton. -The boiling point of straight-chain alkenes is more than branched-chain alkenes just as in alkanes. 4. Melting Point -The melting points of these double-bonded compounds depend upon the positioning of the molecules. -The melting point of alkenes is similar to that of alkanes. -However, cis-isomer molecules have a lower melting point than trans- isomers as the molecules are packed in a U-bending shape. 5. Polarity -Alkenes are weakly polar just like alkanes but are slightly more reactive than alkanes due to the presence of double bonds. -The π electrons which make up the double bonds can easily be removed or added as they are weakly held. -Hence, the dipole moments exhibited by alkenes are more than alkanes. -The polarity depends upon the functional group attached to the compounds and the chemical structures PHYSICAL PROPERTIES OF ALKYNESPhysical Properties Of Alkynes Alkynes are unsaturated hydrocarbons which consist of at least one triple bond between carbon atoms. There are two types of alkynes: terminal and internal. Terminal alkynes are triple-bonded compounds in which a carbon atom shares the triple bond with the carbon at the end of the chain. Internal alkynes are compounds in which the triple bond is between two carbon atoms, none of which are terminal. The general molecular formula of alkynes is CnH2n-2. The physical properties of alkynes are very similar to the physical properties of alkenes. -The uniqueness in the alkyne structure is due to the hybridization. -The ac idity of alkynes, non-polar bonding strength, and linearity are due to the triple bonds in these compounds. -These compounds are slightly soluble in polar solvents and are totally insoluble in water. -Alkynes have the capability of dissolving in organic solvents as the density of the solution is less, which is a characteristic feature of alkenes as well. For example, it has the capability to dissolve in ether solution. Physical Properties of Alkynes The properties of alkynes pretty much follow the same pattern of those of alkanes and alkenes. Alkynes are unsaturated carbon that shares a triple bond at the carbon site All alkynes are odourless and colourless with the exception of ethylene which has a slight distinctive odour. The first three alkynes are gases, and the next eight are liquids. All alkynes higher than these eleven are solids Alkynes are slightly polar in nature The boiling point and melting point of alkynes increases as their molecular structure grows bigger. The boiling point increases with increase in their molecular mass Also, the boiling points of alkynes are slightly higher than those of their corresponding alkenes, due to the one extra bond at the carbon site. Chemical properties of alkynes Terminal Alkynes are acidic in nature. It un-dergoes polymerization and addition reaction. 1. Acidic nature of alkynes: An alkyne shows acidic nature only if it contains terminal hydrogen. This can be explained by considering sp hybrid orbitals of carbon atom in alkynes. The percentage of S-character of sp hybrid orbital (50%) is more than sp2 hybrid orbital of alkene (33%) and sp3 hybrid orbital of alkane (25%). Because of this, Carbon becomes more electronegative facilitating donation of H+ ions to bases. So hydrogen attached to triply bonded carbon atoms is acidic. Addition reactions of alkynes i) addition of hydrogen ii) Addition Of Halogens: When Br2 in CCl4 (Reddish brown) is added to an alkyne, the bromine solution is decolourised. This is the test for unsaturation. iii) Addition Of Hydrogen Halides: Reaction of hydrogen halides to symmetrical alkynes is electrophilic addition reaction. This reaction also follows Markovnikoff’s rule. Addition of HBr to unsymmetrical alkene follows Markownikoff’s rule. iv) Addition Of Water: Alkynes undergo hydration on warming with mercuric sulphate and dilute H2SO4 at 333K to form carbonyl compounds. 3. Ozonolysis: Ozone adds to carbon-carbon triple bond of alkynes to form ozonides. The ozonides are hydrolyzed by water to form carbonyl compounds. The hydrogen peroxide (H2O2) formed in the reaction may oxidise the carbonyl compound to carboxylic acid. 4. Polymerisation: Alkyne undergoes two types of polymerisation reaction (i) Linear Polymerisation: Ethyne forms linear polymer, when passed into a solution of cuprous chloride and ammonium chloride. (ii) Cyclic Polymerisation: Ethyne undergoes cyclic polymeriza-tion on passing through red hot iron tube. Three molecules of ethynepolymerises to benzene. IUPAC Nomenclature of organic compounds According to the Guidelines set by IUPAC, the nomenclature of compounds must follow these steps: 1. The Longest Chain Rule: The parent hydrocarbon must be identified and subsequently named. The parent chain belonging to the compound in question is generally the longest chain of carbon atoms, be it in the form of a straight chain or a chain of any other shape. 2. The Lowest Set of Locants: The carbon atoms belonging to the parent hydrocarbon chain must be numbered using natural numbers and beginning from the end in which the lowest number is assigned to the carbon atom which carries the substituents. 3. Multiple instances of the same substituent: Prefixes which indicate the total number of the same substituent in the given organic compounds are given, such as di, tri, etc. 4. Naming of different substituents: In the organic compounds containing multiple substituents, the corresponding substituents are arranged in alphabetical order of names in the IUPAC nomenclature of organic compounds in question. 5. The naming of different substituents present at the same positions: In the scenario wherein two differing substituent groups are present at the same position of the organic compound, the substituents are named in ascending alphabetical order. 6. Naming Complex Substituents: Complex substituents of organic compounds having branched structures must be named as substituted alkyl groups whereas the carbon which is attached to the substituent group is numbered as one. These branched and complex substituents must be written in brackets in the IUPAC nomenclature of the corresponding compounds. The format of the IUPAC Name of the Compound can be written as: Locant + Prefix + Root + Locant + Suffix 1. Root The Word root indicates the total number of carbon atoms present in the longest carbon chain belonging to the compound. For example, ‘Meth’ refers to a chain with 1 carbon atom and ‘Pent’ refers to a chain with 5 carbon atoms. 2. Suffix The suffix in IUPAC nomenclature is usually a functional group belonging to the molecule which follows the root of the name. It can be further divided into the following types. A Primary Suffix, which is written immediately after the word root as in the case of alkanes, where the suffix is ‘ane’. A Secondary Suffix, which is generally written after the primary suffix is written. For example, compounds having an alkane and alcohol group attached to them will be named as alkanol, with ‘ol’ being the secondary suffix for the alcohol group. In accordance with these norms, the suffix of a compound can be written as a part of the IUPAC name of the given compound. 3. Prefix Prefixes are added prior to the root of the compounds IUPAC nomenclature. Prefixes are very useful since they indicate the presence of side chains or substituent groups in the given organic molecule. These prefixes also offer insight into the cyclic or acyclic natures of the compounds in question. Primary Prefixes Indicate the cyclic or acyclic nature of the given compound. The prefix ‘cyclo’ is used for cyclic compounds, for example. Secondary Prefixes Indicate the presence of side chains or substituent groups. An example of these types of prefixes would be the ‘CH3’ group, which is called the methyl group. Thus, prefixes in IUPAC nomenclature can be broadly classified into primary prefixes and secondary prefixes. The IUPAC nomenclature of alkanes, alkenes, and alkynes are discussed in the subsections below. 1. Alkanes The General formula of alkanes corresponds to CnH2n+2 The suffix ‘ane’ is generally used to describe alkanes. Examples for the nomenclature of alkanes as per IUPAC guidelines include methane for the compound CH4 and Butane for the compound C4H10 2. Alkenes The General formula of alkenes is described as CnH2n The suffix ‘ene’ is used to describe alkenes via IUPAC norms. Examples for the nomenclature of alkenes include the name ethene used to describe the compound given by C2H4 and Propene used to describe the compound given by C3H6 3. Alkynes The General formula of alkynes is CnH2n-2 The suffix ‘yne’ is generally used to describe alkynes. An example of the IUPAC nomenclature of alkynes is: ethyne used to describe the compound given by C2H2 Example of IUPAC Nomenclature Considering the following Example: There exist 9 carbon atoms on the straight chain and the 5th carbon atom (from both ends of the chain) consists of a substituent group which in turn has 3 carbon atoms in a chain. Furthermore, there the first and second carbons of this substituent chain have an additional CH group attached to them.  In the nomenclature of this compound, the 9 membered carbon chain is identified as the parent chain and is numbered. The substituent chain attached to position 5 of the parent chain is 3 members long, with 2 methyl groups attached at positions 1 and 2. Thus the carbon chain substituent group on the parent chain can be called 1,2 dimethyl propane. The name for the substituent chain containing this compound would be 1,2 dimethyl propyl. Substituting this name on the parent chain, the IUPAC name of the compound in question is found to be: 5-(1,2 dimethyl propyl) nonane. IUPAC NOMENCLATURE of ALKANES 1. Identify the longest continuous carbon chain as the parent chain. This chain determines the parent name (or last name) of the alkane. If there are two choices of the same length, then the parent chain is the longest chain with the greatest number of “branches”. The term substituent will be used from now on as the official name for “branch”. 2. Number the chain beginning at the end that is closest to any substituents, thus ensuring the lowest possible numbers for the positions of substituents. 3. Use these numbers to designate the location of the substituent groups, whose names are obtained by changing the “-ane” suffix to “-yl“. The substituents derived from alkane are also called alkyl groups. Figure 2.2a Normal alkyl groups  Figure 2.2b Branched alkyl groups 4. If an alkyl substituent group appears more than once, use the prefixes di, tri, tetra, penta, and hexa (meaning 2, 3, 4, 5, and 6 respectively) for each type of alkyl group. 5. List the substituent groups alphabetically (use the substituent group name from step 3, ignore the prefixes from 4, but include “iso” and “cyclo”). 6. Write the name as a single word. Numbers are separated from letters by “-“; numbers are separated by “,”. Alkane Naming Examples: Figure 2.2c 3-ethylhexane ISOMERISM isomerism is the phenomenon in which more than one compounds have the same chemical formula but different chemical structures. Chemical compounds that have identical chemical formulae but differ in properties and the arrangement of atoms in the molecule are called isomers. Therefore, the compounds that exhibit isomerism are known as isomers. Isomerism Types There are two primary types of isomerism, which can be further categorized into different subtypes. These primary types are Structural Isomerism and Stereoisomerism. The classification of different types of isomers is illustrated below. Structural Isomerism Structural isomerism is commonly referred to as constitutional isomerism. The functional groups and the atoms in the molecules of these isomers are linked in different ways. Different structural isomers are assigned different IUPAC names since they may or may not contain the same functional group. Position Isomerism The positions of the functional groups or substituent atoms are different in position isomers. Typically, this isomerism involves the attachment of the functional groups to different carbon atoms in the carbon chain.  An example of this type of isomerism can be observed in the compounds having the formula C3H7Cl. Functional Isomerism It is also known as functional group isomerism. As the name suggests, it refers to the compounds that have the same chemical formula but different functional groups attached to them. An example of functional isomerism can be observed in the compound C3H6O. Metamerism This type of isomerism arises due to the presence of different alkyl chains on each side of the functional group. It is a rare type of isomerism and is generally limited to molecules that contain a divalent atom (such as sulphur or oxygen), surrounded by alkyl groups. Example: C4H10O can be represented as ethoxyethane (C2H5OC2H5) and methoxy-propane (CH3OC3H7). Tautomerism  A tautomer of a compound refers to the isomer of the compound which only differs in the position of protons and electrons. Typically, the tautomers of a compound exist together in equilibrium and easily interchange. It occurs via an intramolecular proton transfer. An important example of this phenomenon is Keto-enol tautomerism. Ring-Chain Isomerism In ring-chain isomerism, one of the isomers has an open-chain structure whereas the other has a ring structure. They generally contain a different number of pi bonds. A great example of this type of isomerism can be observed in C3H6. Propene and cyclopropane are the resulting isomers, as illustrated below. Stereoisomerism This type of isomerism arises in compounds having the same chemical formula but different orientations of the atoms belonging to the molecule in three-dimensional space. The compounds that exhibit stereoisomerism are often referred to as stereoisomers. This phenomenon can be further categorized into two subtypes. Both these subtypes are briefly described in this subsection. Geometric Isomerism It is popularly known as cis-trans isomerism.  These isomers have different spatial arrangements of atoms in three-dimensional space. An illustration describing the geometric isomerism observed in the acyclic But-2-ene molecule is provided below. Optical Isomerism Compounds that exhibit optical isomerism feature similar bonds but different spatial arrangements of atoms forming non-superimposable mirror images. These optical isomers are also known as enantiomers. Enantiomers differ from each other in their optical activities. Dextro enantiomers rotate the plane of polarized light to the right whereas laevo enantiomers rotate it to the left, as illustrated below. Alkyl Halides An alkyl halide is another name for a halogen‐substituted alkane. The carbon atom, which is bonded to the halogen atom, has sp 3 hybridized bonding orbitals and exhibits a tetrahedral shape. Due to electronegativity differences between the carbon and halogen atoms, the σ covalent bond between these atoms is polarized, with the carbon atom becoming slightly positive and the halogen atom partially negative. Halogen atoms increase in size and decrease in electronegativity going down the family in the periodic table. Therefore, the bond length between carbon and halogen becomes longer and less polar as the halogen atom changes from fluorine to iodine. Physical properties Alkyl halides have little solubility in water but good solubility with nonpolar solvents, such as hexane. Many of the low molecular weight alkyl halides are used as solvents in reactions that involve nonpolar reactants, such as bromine. The boiling points of different alkyl halides containing the same halogen increase with increasing chain length. For a given chain length, the boiling point increases as the halogen is changed from fluorine to iodine. For isomers of the same compound, the compound with the more highly‐branched alkyl group normally has the lowest boiling point. Table summarizes data for some representative alkyl halides. Alkyl halides are named using the IUPAC rules for alkanes. Naming the alkyl group attached to the halogen and adding the inorganic halide name for the halogen atom creates common names. Primary alkyl halides In a primary (1°) halogenoalkane, the carbon which carries the halogen atom is only attached to one other alkyl group.Some examples of primary alkyl halides include: Secondary alkyl halides In a secondary (2°) halogenoalkane, the carbon with the halogen attached is joined directly to two other alkyl groups, which may be the same or different. Examples: Tertiary alkyl halides In a tertiary (3°) halogenoalkane, the carbon atom holding the halogen is attached directly to three alkyl groups, which may be any combination of same or different. Examples: Classification of Alkyl Halide Alkyl Halide can be classified on the basis of various aspects, and they are as follows. A. Number of Halogen Atoms Here, the classification mainly depends on whether they contain one, two, or more halogen atoms in their structure. Under this category, we have, 1. Mono Haloalkane: Example: CH3-CH2-X [Where X can be Cl, F, Br or I] 2. Dihaloalkane: Example: X-CH2-CH2-X [Where X can be Cl, F, Br or I] 3. Trihaloalkane: Example: X-CH2-CHX-CH2-X [Where X can be Cl, F, Br or I B. The Position of Halogen Atom Along the Chain of Carbon Atom The classification depends on how the halogen atom is positioned on the chain of carbon atoms. Primary alkyl halide Secondary alkyl halide Tertiary alkyl halide Primary Alkyl Halide In this type of haloalkanes, the carbon which is bonded to the halogen family will be attached to only one other alkyl group. It doesn’t matter how much a bulky group is attached to it. Alkyl Halide Properties I.Alkyl halides are colourless when they exist in pure form. But, bromides and iodides develop colour when exposed to light. Many volatile halogen compounds have a sweet smell. II.Boiling and Melting Points: Methyl chloride, methyl bromide, ethyl chloride and some chlorofluoromethanes are in the form of gas at room temperature. Higher members are liquids or solids. molecules of organic halogen compounds are polar in nature. Due to greater polarity and greater molar mass as compared to the parent hydrocarbon, the intermolecular force of attraction is stronger in halogen derivatives. So, the boiling points of chlorides, bromides and iodides are considerably higher than that of the hydrocarbon with the same molecular mass. The attraction gets stronger as the size and number of electrons increase. The boiling points of alkyl halides will decrease in the order RI > RBr > RCl > RF. Density: Bromo-derivatives, iodo derivatives and polychloro derivatives of hydrocarbons are heavier than water. The density increases with an increase in the number of carbon atoms, halogen atoms and atomic mass of halogen atoms. Solubility: The haloalkanes are less soluble in water. To dissolve haloalkanes in water, energy is required to overcome the attraction between the haloalkane molecule and break the hydrogen bonds between the water molecules for haloalkanes. Very less amount of energy is released when new attractions between the haloalkanes and the water molecules are formed, which is not as strong as the original hydrogen bonds in water. So, the solubility of haloalkanes in water is less. But, the haloalkanes will dissolve in the organic solvent more than in the water. Because of this, the complex interaction between the haloalkanes and the creative molecules has the same potential as those broken by the unique and molecular haloalkanes. Chemical Reactions of alkyl halides The chemical reaction of haloalkanes can be divided into three categories: Nucleophilic substitution reaction Elimination reaction Reaction with metals Nucleophilic Substitution Reaction In this type of reaction, a nucleophile reacts with haloalkane, which has a partial positive charge on the carbon atom that is bonded to halogen. A substitution reaction takes place, and the halogen atom called leaving group leaves as the halide ion. Since the substitution reaction is initiated by a nucleophile, it is called a nucleophilic substitution reaction. Example: Nucleophilic Substitution Reaction: It is one of the most useful classes of organic reactions of an alkyl halide in which halogen is bonded to sp3 hybridized carbon. Elimination Reaction: When a haloalkane having a hydrogen atom is heated with an alcoholic solution of potassium hydroxide, it will lead to the elimination of a hydrogen atom from the β-carbon atom and a halogen atom from the α-carbon atom. As a result, an alkene is formed as one of the products. Since the β-hydrogen atom is involved in elimination, it is often called a β-elimination reaction. Elimination Reaction If there is any possibility of the formation of more than one alkene due to the presence of more than one β – hydrogen atom, usually one alkene is formed as the main product. Reaction with Metals: Most organic chlorides, bromides and iodides react with certain metals to give compounds containing carbon-metal bonds. Such compounds are known as organometallic compounds. The product is formed by the reaction of haloalkanes with magnesium metal in dry ether. Synthesis of Alkyl Halides Uses of Alkyl Halide Many organic compounds containing halogens occur in nature, and some of them are clinically useful. These classes of compounds find good applications in industry as well as in day-to-day life. They are used as solvents for relatively non-polar compounds and as starting materials for the synthesis of a wide range of organic compounds. A chlorine-containing antibiotic, chloramphenicol, produced by soil microorganisms, is very effective for the treatment of typhoid fever. Some fully fluorinated compounds are considered potential blood substitutes in surgery. They are used as synthon equivalents in organic synthesis. They were previously used as refrigerants and propellants. They are also used in fire extinguishers. ALKANOLS-CLASSIFICATION-SOURCES-USES OF ALKANOLS, Introduction: Alkanol are the group of compounds in which the hydrogen atom(s) of alkanes have been substituted with the hydroxyl (-OH) functional group. Alkanols are usually termed to as 'alcohols'. We are as well familiar that the general formula of Alkanols is CnH2n+1OH and are named by replacing the 'e' of the alkane name via 'ol'. For example - methanol and ethanol from methane and ethane. Fig: Methanol and ethanol A simple general representation for Alkanols is R-OH; here 'R' symbolizes an alkyl group. Whenever essential, the position of the -OH group is illustrated numerically, example: propanol. The carbon atoms are numbered in the longest chain. The position of the OH group finds out the numbers. Let us study the structures shown below. Fig: Alkanols The hydroxyl group is one of the most significant functional groups of naturally occurring molecules like carbohydrates and nucleic acids. These are complex alkanols however the main concern are simple alkanols which are made up from petroleum-derived hydrocarbons. Classification of Alkanols: Alkanols are categorized as primary, secondary or tertiary based on whether the OH functional group is linked to a primary, secondary or tertiary carbon atom, example: Sources of Alkanols: General methods of preparation: (a) Hydrolysis of halogenoalkanes or alkyl halides: Alkyl halides are the compounds made by replacing one of the hydrogen of an alkane with a halogen (Cl or Br or I). Whenever alkyl halides are treated by dilute aqueous sodium hydroxide, the halogen is substituted by - OH groups therefore making an alkanol. R-Cl + Na+ + OH- → R-OH + NaCl Example: CH3CH2Cl + NaOH → CH3CH2-OH + NaCl Ethyl chloride Ethanol (b) Hydration of alkenes: The Alkenes react with steam whenever passed over phosphoric (v) acid catalyst at 300°C and 70 atmosphere. For illustration: CH2 = CH2 + H2O → (H3PO4 at 300oc + 70 atms) → CH3-CH2-OH The method, as illustrated in the equation, is mainly used industrially for the production of ethanol and some higher alkanols. Manufacture of alkanols: a) Methanol: Methanol is mainly made up from mixture of carbon (II) oxide and hydrogen (that is, obtained from either water gas or synthesis gas) in the presence of a catalyst. C(coke) + H2O(g) → CO + H2 (water gas) CH4 (natural gas) + H2O (g) → CO + 3H2 (synthesis gas) CO + 2H2 → (ZnO + Cr2O3 at 400oc and 300 atm) → CH3OH (b) Ethanol: - From ethene: The main source of ethanol industrially is through hydration of alkenes as illustrated above. - By fermentation: The fermentation method of obtaining ethanol from starch materials is still admired. Fermentation is basically the decomposition of complex organic compounds example: carbohydrates, into simpler compounds via the action of enzymes. Materials like - sugar, guinea-corn, rice, cassava, maize, potatoes, wheat, barley and so on can be employed as the source of glucose from which the ethanol is derived.  From starchy materials: The material is crushed and treated by steam to extract the starch from them. Malt, made up from partially germinated barley, is added and then kept at around 50°C for one hour. The enzyme diastase, present in the malt, catalyses the conversion of starch to the maltose. 2(C6H10O5)n + nH2O → (diastase) → nC12H22O11 Starch maltose The yeast is then added at room temperature. This causes fermentation, the enzyme maltase in the yeast, transforms the maltose to glucose and the other enzyme zymase in yeast, then decomposes the glucose into ethanol and carbon (iv) oxide. C12H22O11 (aq) + H2O → (maltase) → 2C6H12O6 (aq) Glucose C6H12O6 → (zymase) → 2C2H5OH + 2CO2 ethanol -From molasses: In countries such as Brazil, U.S.A; where the production of sugar cane is high, the main raw material for ethanol production is molasses, a syrupy liquid which remains after the crystallization of sugar. It includes sucrose, a kind of sugar. Whenever molasses is mixed by yeast, the enzyme invertase in yeast, transforms the sucrose to two simple isomeric sugars, glucose and fructose, which are both fermented to ethanol through zymase. C12H22O11 + H2O → (invertase) → C6H12O6 + C6H12O6 → (zymase) → 4C2H5OH + 4CO2 Glucose Fructose -From palm wine: In some portions of Africa example: Nigeria, South Africa and Ghana; local gin is obtained by fermenting palm wine which is rich in sugar. Fresh palm wine includes sugar and yeast, which on storage in large earthenware pots or drums for 3 to 4 days, is fermented to ethanol. The resultant solution is then distilled to get the clear ethanol generally termed as gin. (c) Purification of ethanol: The ethanol achieved from the fermentation method can only provide a maximum concentration of 18%, as the yeast cells die above this concentration. For commercial use, ethanol is needed in different compositions and to accomplish further concentration and purification, fractional distillation is used. For the alcoholic beverages, different concentrations of ethanol are employed and their flavor differs with raw material fermented. The table illustrated below represents the percentage of ethanol and the method of preparation. Table: Kinds of alcoholic beverages Raw material Alcohol beverage % Ethanol (v/u) Method of preparation Barley, Wheat Beer e.g. star 3-8 Fermentation Grapes/Rice Wines 8 - 18 Fermentation Barley, Wheat, Whisky/Spirit/Brandy30 - 60 Fermentation & Grapes Distillation The commercial ethanol is sold as pure spirit or rectified spirit or methylated spirit having 95% ethanol. Whenever sold to the public, 5% methanol, which is toxic, is added to prevent it being used as a drink. The physical and chemical properties of alcohols are mainly due to the presence of hydroxyl group. Alcohols are organic compounds in which a hydrogen atom of an aliphatic carbon is replaced with a hydroxyl group. Thus, an alcohol molecule consists of two parts; one containing the alkyl group and the other containing functional group hydroxyl group. They have a sweet odour. They exhibit a unique set of physical and chemical properties. Physical Properties of Alcohol 1. The Boiling Point of Alcohols Alcohols generally have higher boiling points in comparison to other hydrocarbons having equal molecular masses. This is due to the presence of intermolecular hydrogen bonding between hydroxyl groups of alcohol molecules. In general, the boiling point of alcohols increases with an increase in the number of carbon atoms in the aliphatic carbon chain. On the other hand, the boiling point decreases with an increase in branching in aliphatic carbon chains, the Van der Waals force decreases with a decrease in surface area. Thus primary alcohols have a higher boiling point. 2. Solubility of Alcohols The solubility of alcohol in water is governed by the hydroxyl group present. The hydroxyl group in alcohol is involved in the formation of intermolecular hydrogen bonding. Thus, hydrogen bonds are formed between water and alcohol molecules which make alcohol soluble in water. However, the alkyl group attached to the hydroxyl group is hydrophobic in nature. Thus, the solubility of alcohol decreases with the increase in the size of the alkyl group. 3. The Acidity of Alcohols Alcohols react with active metals such as sodium, potassium etc. to form the corresponding alkoxide. These reactions of alcohols indicate their acidic nature. The acidic nature of alcohol is due to the polarity of –OH bond. The acidity of alcohols decreases when an electron-donating group is attached to the hydroxyl group as it increases the electron density on the oxygen atom. Thus, primary alcohols are generally more acidic than secondary and tertiary alcohols. Due to the presence of unshared electrons on the oxygen atom, alcohols act as Bronsted bases too. Chemical Properties of Alcohols Alcohols exhibit a wide range of spontaneous chemical reactions due to the cleavage of the C-O bond and O-H bond. Some prominent chemical reactions of alcohols are: 1. Oxidation of Alcohol Alcohols undergo oxidation in the presence of an oxidizing agent to produce aldehydes and ketones which upon further oxidation give carboxylic acids. 2. Dehydration of Alcohol Upon treatment with protic acids, alcohols undergo dehydration (removal of a molecule of water) to form alkenes. Dehydration of alcohol Catalytic Reduction of Butanal Reduction of butanal produces butanol. This is occurs by hydrogenation reaction. Here the hydrogens are added to the carbon – oxygen double bond, it is converted to a carbon – oxygen single bond, as the carboxyl oxygen becomes a hydroxyl group. Addition of hydrogen to a carbon-carbon double bond to form an alkane is a reduction reaction that is also called catalytic hydrogenation. Hydrogenation of a double bond is a thermodynamically favourable reaction because it forms a more stable (lower energy) product. Uses of ethanol: 1) This is used as solvent for resins, polishes, varnishes, liquid soaps, perfumes, drugs and paints. 2) It is employed as a fuel, either by itself or mixed by petrol, in rockets and racing cars. 3) It is employed as an anti-freeze in the automobile radiator. 4) It is present in numerous alcoholic beverages. 5) It is employed for sterilization and preservation of the specimens and food. 6) It is employed as raw material in the manufacture of chemical example: ethanol, trichloromethane and ethoxyethane. POLYHYDRIC ALCOHOL A family of organic compounds containing two or more hydroxyl groups (—OH) used as solvents in printing inks, characterized by their much lower volatility (ability to evaporate quickly at low temperatures) than monohydric alcohols. Examples of polyhydric alcohols are glycol and glycerol. The simplest example of an alcohol with more than one hydroxyl group is methanediol or methylene glycol, HOCH2OHHOCH2OH. The term “glycol” indicates a diol, which is a substance with two alcoholic hydroxyl groups. Methylene glycol is reasonably stable in water solution, but attempts to isolate it lead only to its dehydration product, methanal (formaldehyde): This behavior is rather typical of gem-diols (gem == geminal, that is, with both hydroxyl groups on the same carbon atom). The few gem-diols of this kind that can be isolated are those that carry strongly electron-attracting substituents such as the following: Polyhydric alcohols in which the hydroxyl groups are situated on different carbons are relatively stable, and, as we might expect for substances with multiple polar groups, they have high boiling points and considerable water solubility, but low solubility in nonpolar solvents: 1,2-Diols are prepared from alkenes by oxidation with reagents such as osmium tetroxide, potassium permanganate, or hydrogen peroxide (Section 11-7C). However, ethylene glycol is made on a commercial scale from oxacyclopropane, which in turn is made by air oxidation of ethene at high temperatures over a silver oxide catalyst Ethylene glycol has important commercial uses. It is an excellent permanent antifreeze for automotive cooling systems because it is miscible with water in all proportions and a 50%50% solution freezes at −34o−34o (−29oF)(−29oF). It also is used as a solvent and as an intermediate in the production of polymers (polyesters) and other products The trihydric alcohol, 1,2,3-propanetriol (glycerol), is a nontoxic, water-soluble, viscous, hygroscopic liquid that is used widely as a humectant (moistening agent). It is an important component of many food, cosmetic, and pharmaceutical preparations. At one time, glycerol was obtained on a commercial scale only as a by-product of soap manufacture through hydrolysis of fats, which are glyceryl esters of long-chain alkanoic acids. The major present source is by synthesis from propene (The trinitrate ester of glycerol (nitroglycerin) is an important but shock-sensitive explosive: CARBONYL COMPOUND (ALKANALS AND ALAKANONES) Alkanones and alkanals together are referred to as carbonyl compounds because they are organic molecules which contain the carbonyl, C=O, functional group: The chemistry of aldehydes and ketones is influenced by the presence of a carbonyl group in them. In aldehydes, the carbonyl group is attached to a carbon and hydrogen, whereas in ketones it is bonded to two carbon atoms Alkanals: C=O occurs at the end of a carbon chain The general structure of an alkanal is R-CHO (R is an alkane chain or a hydrogen atom) Alkanones: C=O does not occur at the end of a carbon chain The general structure of an alkanone is R-CO-R' (R and R' are both alkane chains). Alkanals (R-CHO) belong to a class of organic molecules known as aldehydes. Alkanones (R-CO-R') belong to a class of organic molecules known as ketones. Naming Aldehydes  According to the IUPAC system of nomenclature -al is attached as a suffix to parent alkane for the naming of aldehydes. For example, H2C=O is named as per the IUPAC system as methanal, commonly known as formaldehyde. The aldehyde group is always attached at the end of the main carbon chain, and hence the 1st position in the numbering is always assigned to it. It is not always necessary to include numbering in the naming. Instead of IUPAC names, aldehydes and ketones are also called by their common names. For aldehydes and ketones, the names are reflected in Greek and Latin terms. Greek letters such as α, β etc. are used for the location of the substituents in the carbon chain. The α-carbon is directly attached to the aldehyde group, β-carbon is attached to the carbon adjacent to the aldehyde group and so on. Naming Ketones according to IUPAC guidelines, the suffix –one is assigned for the ketones. The carbonyl group can be located anywhere within the main chain and the position is decided by the location number. The numbering of the chain usually starts from the end such that the carbonyl carbon gets the lowest number. But there are some ketones such as propanone and phenyl ethanoid which do not require any number locator as there is only one possible site for ketone carbon. If there are more than one functional groups in a molecule then the functional group with the higher priority is named first and the other ones are considered as a substituent. If there is both a ketone and aldehyde group in a molecule then the aldehyde group is given priority over ketone while naming. Physical properties : of alkanones and alkanals are similar and are related to the polarity of the C=O functional group and the length of the carbon chain: 1. Melting points and boiling points are greater than for alkanes of comparable alkane chain length but less than for the corresponding alkanol. 2. Melting points and boiling points increase as the length of the carbon chain increases. 3. Short chain alkanals and alkanones are soluble in water, but solubility decreases as the length of the carbon chain increases. Chemical properties of alkanones and alkanals: 1. Oxidation (addition of oxygen using an oxidising agent): (a) Alkanals can be oxidised to alkanoic acids (b) Alkanones can not be readily oxidised. 2. Reduction (addition of hydrogen using a reducing agent): (a) Alkanals can be reduced to primary alkanols. (b) Alkanones can be reduced to secondary alkanols. Importance of Carbonyl compounds (aldehydes and ketones) are: 1. important in synthetic chemistry (that is, are used to make other industrial and/or commercial compounds) 2. found in nature as odour and flavour agents