Introduction to Organic Chemistry

Meaning of Organic Chemistry

• Organic means pertaining to life.
• Substances from living sources like plants and animals are organic compounds.
• The study of organic compounds is known as organic chemistry.
• Substances from minerals and non-living sources are inorganic compounds.
• The study of inorganic compounds is known as inorganic chemistry.
• The "vital force" theory was disproven by Friedrich Wöhler, who synthesized urea in a lab.

Organic Compounds

• Organic compounds are carbon compounds
• Organic chemistry studies carbon compounds
• It excludes oxides of carbon, metallic carbonates, metal cyanides, and metal carbides.

Sources of Organic Compounds

• Plants: sugar and starch
• Animals: urea and protein
• Coal: dyes and drugs
• Petroleum: petrol, gasoline, and fuel gases
• Fermentation: ethyl alcohol and acetic acid
• Wood: methyl alcohol and acetone

Applications of Organic Chemistry

• Organic compounds are extremely useful in daily life.
• Soaps, shampoos, powders, perfumes, clothes, food, fuels, medicines, explosives, dyes, and insecticides are all organic compounds.

Comparison of Organic and Inorganic Compounds

• Identification: Organic compounds contain C, H, and O, while inorganic compounds contain all elements except C-H.
• Nature of compounds: Organic compounds are covalent, while inorganic compounds are electrovalent, ionic, or covalent.
• Melting and boiling points: Organic compounds have low melting and boiling points, inorganic have high
• Solubility in water: Organic compounds have low solubility in water, inorganic have high
• Conductivity: Organic compounds are poor conductors, while inorganic compounds are good conductors.
• Volatility: Organic compounds are volatile, inorganic compounds are non-volatile.
• Catenation property: Organic compounds exhibit catenation, while inorganic compounds generally do not.
• Exhibition of colors: Organic compounds are generally colorless, while inorganic compounds are generally colored.
• Rate of reactions: Organic compounds have slow reaction rates, while inorganic compounds have fast reaction rates.
• Occurrence: Organic compounds are found in living things, while inorganic compounds are found in non-living things.
• Biodegradability: Organic compounds are usually biodegradable, while inorganic compounds are non-biodegradable.
• Examples: Organic compounds include enzymes, protein, DNA, RNA, and fuels, while inorganic compounds include metals, non-metals, and salts.

Unique Nature of Carbon Atoms

• Carbon exhibits tetravalency, catenation, and isomerism.

Tetravalency of Carbon Atom

• Carbon has four valence electrons (atomic number = 6, electronic configuration = 2, 4).
• Carbon forms four covalent bonds by sharing its four electrons to attain an octet.
• Forming four covalent bonds is tetravalency.

Catenation

• Carbon atoms link (self-linking) to form long chains, known as catenation
• Self-linking of atoms through covalent bonds forms straight, branched, and cyclic chains of different sizes.

Isomerism

• Isomerism occurs when compounds have the same molecular formula but different structural formulas.
• Isomers differ in physical and chemical properties.

Types of Organic Compounds

• Hydrocarbons contain carbon and hydrogen atoms
• Two main groups of hydrocarbons: aliphatic (open) and cyclic (closed) chain compounds.

Aliphatic (open) compounds

• Saturated compounds: alkanes are the simplest open chain hydrocarbon with the formula CnH2n+2 where n is a natural number.
  • All four valencies of carbon are satisfied by a single covalent bond.
• Unsaturated compounds: contain double or triple covalent bonds between two adjacent carbon atoms.
  • Further classified as alkenes (double bond) and alkynes (triple bond).

Cyclic or Closed Chain or Ring Chain Compounds

• These compounds contain three or more carbon atoms
• Two Types: alicyclic and aromatic

Alicyclic Compounds

• Ringed carbon compounds with three or more carbon atoms in a closed structure.

Aromatic compounds:

• Hydrocarbons with at least one benzene ring.
• Benzene ring: a ring structure of six carbon atoms that contain carbon single and carbon-carbon double bonds in alternate positions.

Homologous Series

• A group of organic compounds has a similar structure and chemical properties.
• Successive compounds differ by a CH2 group (Alkanes, alkenes, alkynes)

Characteristics of a Homologous Series

• All members share the general formula.
• Each member differs from the preceding one by a CH2 group and a molecular mass of 14 a.m.u.
• Physical properties change gradually.
• Members have similar chemical properties.
• All members can be prepared using the same general method of preparation.

Significance of the Homologous Series

• Determine the nature of any member of that family of compounds.
• Predict the properties of even members that are yet to be prepared.
• Homologous series saves learning time.

Nomenclature

• Nomenclature is the system of assigning names to organic compounds.
• Two Systems: Trivial system and IUPAC (International Union of Pure and Applied Chemistry) system.
• The name of an organic compound consists of three parts: Root Word, Suffix, Prefix

Root Word

• Depends on the number of carbon atoms present in the longest carbon chain selected.

Suffix

• Follows the root word and represents the nature of the bond in a carbon - carbon atom.

Prefix

• It denotes the substituent, alkyl or functional group and its position in the carbon chain.

Alkyl Group

• An alkyl group is obtained by removing one hydrogen atom from an alkane molecule.

Functional Group

• A functional group is an atom or group of atoms joined in a specific manner.
• Functional groups are responsible for the characteristic chemical properties of organic compounds
• Examples: hydroxyl group (-OH), aldehyde group (-CHO), and carboxylic acid group (-COOH).

Characteristics of Functional Groups

• Compounds with the same functional group have similar chemical properties.
• Compounds with different functional groups have different physical and chemical properties.
• A homologous series contains a particular type of functional group.

Structure

• Structural formula: Shows how atoms of different elements are linked together in a molecule

• Abbreviated/Condensed formula: Representing a molecule in a simplified form (e.g., butane)

• Carbon skeleton: Shows only the linking of carbon atoms in a molecule

Rules of Nomenclature of Organic Compounds

• Rule 1: Select the longest carbon chain as the root.
• Rule 2: Branch chains are substituents, positions being indicated by the number of carbon atoms to which they are attached.
• Rule 3: Number the carbon atoms of the longest chain so that the alkyl groups (substituents) get the smallest possible number.
• Rule 4: Indicate the position(s) of the alkyl group(s) by writing the position and name of the alkyl group just before the name of the parent hydrocarbon.
• Rule 5: Label multiple alkyl groups with Greek numerical prefixes.
• Rule 6: If any functional group is present in the chain, then number the carbon atoms so that the functional group gets the smallest possible number.
• Rule 7: For different types of substituents attached to the chain, they are arranged and named alphabetically.

Isomers

• Isomers: Compounds having the same molecular formula but different structural formula.
• Isomerism (iso = same, meros = parts): Isomers differ in physical and/or chemical properties.

Main Causes of Isomerism

• Difference in the mode of linking of atoms.

Chain Isomerism

• When two or more compounds have a similar molecular formula but are different in the arrangement of carbon atoms in straight or branched chains.
• Compounds are referred to as chain isomers, and the phenomenon is termed as chain isomerism.

Position Isomerism

• When two or more compounds with the same molecular formula differ in the position of the substituent atom or functional group on the carbon atom
• Position isomers and this phenomenon are termed position isomerism.

Alkanes

• Alkanes are hydrocarbons with single covalent bonds: CnH2n+2.
• All four valencies of carbon are fully satisfied

Unreactive Hydrocarbons

• Under ordinary conditions alkanes are relatively unreactive
• Alkanes are also known as paraffins (parum-little, affinis - affinity).

Sources of Alkanes

• The principal sources of alkanes are natural gas and petroleum.

Isomerism for Alkanes

• Alkanes with more than three carbon atoms form isomers
• They form chain isomerism.
  • For example: butane has 2 and pentane has 3.

Methane (Marsh Gas)

• Formed due to the fermentation of cellulose.
• Present in the air exhaled by animals whose food contains cellulose.
• Methane is contained in intestinal gases and in the blood of animals and human beings.
• Cavities in coal contain 90% methane, referred to as 'fire-damp'.
• Methane is produced by dry distillation of wood, peat, or coal.

Ethane

• Ethane occurs in the extent of 10-20 percent along with methane.

Structure of Methane

• Methane has a tetrahedron shape.

Laboratory Preparation of Methane

• Reactants: Sodium ethanoate (sodium acetate) and soda lime.
• Procedure: Heat a mixture of sodium ethanoate (sodium acetate) and soda lime is in a hard glass test tube.
• Reaction: CH3COONa + NaOH → Na2CO3 + CH4↑
• Collection: Collect the gas evolved by downward displacement of water (since it is soluble in water and is lighter than air).

Laboratory Preparation of Ethane

• Reactants: Sodium propanoate (sodium propionate) and soda lime.
• Procedure: Heat the mixture of sodium propionate and soda lime is in a boiling tube.

Methods of Preparation of Methane and Ethane

• Iodomethane (methyl iodide) and bromoethane (ethyl bromide) are reduced by nascent hydrogen at ordinary room temperature

  • CH3I + 2[H] → CH4 + HI
  • C2H5Br + 2[H] → C2H6 + HBr

• When water is added at room temperature to aluminium carbide, methane is prepared

  • Al4C3 + 12H2O → 3CH4 + 4AI(OH)3

• When methyl iodide or methyl bromide is warmed with sodium metal in the presence of dry ether, ethane is produced

Wurtz Reaction

• 2CH3I + 2Na → H3C - CH3 + 2Nal
• This reaction is useful for preparing symmetrical alkanes.

Physical Properties

• Methane:
• It is a colorless and an odorless gas.
• Its melting point is -183 °C and its boiling point is -162 °C.
• Methane It is negligible soluble in water but soluble in organic solvents.
• Ethane:
• It is a colorless, odorless, tasteless, and non-poisonous gas.
• Its melting point is -172 °C and its boiling point is -89 °C.
• Ethane is sparingly soluble in water but wholly soluble in organic solvents like alcohols, acetone, and ether.

Chemical Properties

• Complete Combustion

• Methane and ethane burn in air with a bluish non sooty flame.

• They form carbon dioxide and water vapor.

• Combustion in insufficient supply of air:

• When alkanes burn in an insufficient supply of air (oxygen).

• Carbon monoxide and water are formed.

• Substitution Reaction:

• Reaction with Halogens:

• Alkanes react with chlorine, bromine, or iodine in the presence of sunlight or ultraviolet light to give halogen-substituted products that are commonly known as alkyl halides.

• Methane reacts with chlorine in diffused sunlight, or when heated to 600 K, gives chloromethane

  • CH4 + Cl2 → CH3CI + HCI

• Catalytic oxidation of alkanes

• Alkanes give alcohols or aldehydes or carboxylic acids, according to the reaction conditions.

• When a mixture of methane and oxygen in the ratio 9:1 by volume is compressed to about 120 atm pressure and passed over copper tubes at 475 K, methyl alcohol is formed. 2CH4 + O2 → 2CH3OH

(ii) When a mixture of methane and oxygen is passed through heated molybdenum oxide (MoO), the mixture is oxidized to methanal (formaldehyde). CH4 + O2 → HCHO + H2O (iii) When a manganese-based catalyst is used at 100°C, methane can be oxidised to methanoic acid (formic acid). 2CH4 + 3O2 → 2HCOOH + 2H2O

HYDRCARBONS: ALKENES

• Alkenes are also called olefins (oil-forming).
• Because members of alkenes are treated with chlorine or bromine, lower members of alkenes form oily products when they are treated with chlorine or bromine.

Occurrence

• Alkenes are reactive, alkenes seldom occur free in nature.
• Alkenes occur in minute quantities in coal gas.
• Alkenes are produced on a large scale by the cracking of petroleum.

Ethene

• Ethene is the first member of the alkene series It is present in natural gas.
• Ethene occurs in small amounts, it occurs as a plant hormone and is responsible for the ripening of fruits.

Structure of Ethene

• Ethane is a planar molecule

Preparation of Ethene (Ethylene)

(i) Dehydration of ethyl alcohol

• Reactants: Ethanol and conc. sulphuric acid. Procedure: Take one part of ethyl alcohol in a flask. Add two parts of concentrated sulphuric acid and heat gradually to about 170°C. Ethene gas is evolved.

Collection of Ethene

• Collect the gas evolved by water displacement: because it is an inflammable gas and insoluble in water. Reactants: Ethanol and conc. sulphuric acid . Reaction:

C2H5OHConc. H2SO4160°-170°C⟶CH2 = CH2 + H2O EthanolEthene Water

• Ethene can aslo be prepared by passing ethanol vapours through a tube containing alumina (Al2O3) at 350°C. Reaction: C2H5OH → C2H4 + H2O

(ii) Dehydrohalogenation: Ethene is prepared by dehydrohalogenation of ethylhalide or haloethane by alcoholic hot conc. potassium hydroxide. Reaction: C2H5CI + KOH → C2H4 + KCI + H2O

Properties of Alkenes

(i) Its melting point is -169°C and boiling point is -102°C. (ii) It is sparingly soluble in water but highly soluble in organic solvents like alcohol, ether and chloroform.

Chemical Properties

1. Additional Reactions (i) Addition of hydrogen (hydrogenation): When ethene and hydrogen are passed over at 200 degrees C (ii) Addition of halogens (halogenation): Reaction with fluorine is explosive, hence the compound formed is not stable HYDRCARBONS: ALKYNES The aliphatic hydrocarbons that contain a triple bond (-C ≡ C-), i.e., acetylenic bond, between two carbon atoms are known as alkynes. Ethyne: Ethyne is the first member of the alkyne series. Ethyne being an unsaturated hydrocarbon, is not found in free state. Sources: Traces of ethyne are present in coal gas Structure of Ethyne: The shape of ethyne molecule is linear. Laboratory preparation of ethyne Reactants: Water and calcium carbide. Properties of Ethyne: Chemical Properties: Ethyne is a colourless gas with an ether. Addition Reactions AlKYNES: Aliphatic hydrocarbons containing a triple bond (-C≡C-), also known as acetylenic bond.

Ethyne

First of the alkyne series; not found in free state due to its unsaturated nature. Sources: Traces of ethyne are present in coal gas. Structure: Shape of molecule is linear. Lab preparation Reactants: Water and calcium carbide (CaC2)

Reaction

CaC2 + 2H2O → Ca(OH)2 + C2H2 (Acetylene) The air of the flask is displaced with oil or some inert gas. Physical Properties: The one prepared from calcium carbide has garlic odour Properties of Ethyne: Chemical Properties:

Note: Reactants

First stage: Reaction C2H2 + H2 à C2H4 ( Ethene)

• C2H2 plus H2 = the product is Second stage of reaction: C2H4 + H2 à C2H6 ( Ethane) (ii) Addition of Halogens: C2H2 + Cl2 plus 2C à 2HClHALCOHOLS ALCOHOLS Alcohols are the hydroxyl (-OH) derivatives of alkanes. They are formed by replacing one or more hydrogen atoms of the alkane with an OH group. Homologous series of alcohols and their structural formulae are given in Table. Alcohols can be monohydric, i.e., with one(-OH) group attached to the carbon atom. Example: Methyl alcohol (CH3OH) and ethyl alcohol (С2Н5ОН). ETHANOL (C2H5OH) Alcohol can be prepared by the hydrolysis of alkyl halides (haloalkanes) on reaction with a hot dilute alkali or when an alkyl halide is boiled with aqueous alkalis. ##ETHANOL. This is most commonly used commercial alcohol Industrial method (large scale method When concentrated sulphuric acid is added to ethene (obtained from cracking of petroleum) at a temperature Structure of molecule.

They can be dihydric, i.e., with two -OH groups attached to the carbon atom. Physical properties Physical PROPERTIES:

Nature: They are inflammable volatile liquids. They are soluble in water as well as in org.Insolvents. Properties of alcohols Physical properties: B. Chemical properties Alcohols are a reactive class of compounds. Chemical properties: Acids, which are a group with many important properties

1. Combustion Alcohol burns readily in air to produce carbon dioxide and water Ethanol burns with a pale blue flame. Carbonate/hydrogen - they all react in the exact same way across the board in similar situations.

CARBOXYLIC ACIDS

Organic acids are important in many aspects

An organic compound containing the carboxyl group (-COOH) is known as carboxylic acid. The common chemical name for something we come across every other day: ACETIC ACID. The chemical name for this is ethanoic acid General formula: CnH2n+1COOH (or RCOOH) Functional Group: IUPAC name: IUPAC name is given by replacing the 'e' of the corresponding alkane by 'oic acid', because they are derived from alkanes by replacing one hydrogen atom with the carboxyl (- COOH) group. Thus, they are also known as Alkanoic acids.

ETHANOIC ACID (ACETIC ACID) CH3COOH

Structural formula: We find the name 'ACEUTUM', that means Vinegar. The amount: In 4-5% of what you get: It has many physical properties.

1. Physical state: Pure ethanoic acid is a colourless liquid.
2. Odour Chemical properties are related to this acid.