Chapter 03 | Class 10 Chemistry | Federal Board PDF

# 11 Organic Chemistry This is 13 days lesson (period including homework) ## Objectives - Recognize structural, condensed and molecular formulas of the straight chain hydrocarbons up to ten carbon atoms. - Identify some general characteristics of organic compounds. - Explain the diversity and...

# 11 Organic Chemistry This is 13 days lesson (period including homework) ## Objectives - Recognize structural, condensed and molecular formulas of the straight chain hydrocarbons up to ten carbon atoms. - Identify some general characteristics of organic compounds. - Explain the diversity and magnitude of organic compounds. - List some sources of organic compounds. - List the uses of organic compounds. - Recognize and identify molecule's functional groups. - Distinguish between saturated and unsaturated hydrocarbons. - Name the alkanes up to decane. - Convert alkanes into alkyl radicals. - Differentiate between alkane and alkyl radicals. - Define functional group. - Differentiate between organic compounds on the basis of their functional groups. - Classify organic compounds into straight chain, branched chain and cyclic compounds. - Identify carboxylic acids, phenols, amines, aldehydes and ketones in terms of functional groups in the lab. - Distinguish between saturated and unsaturated compounds using iodine, bromine and potassium permanganate solutions. - Show how pharmaceutical chemists work towards the partial and total synthesis of effective new drugs. - Explain how substances produced by plants and animals can also be produced in the lab. ## Introduction The study of carbon containing compounds and their properties is called organic chemistry. However, a few compounds of carbon such as carbon dioxide, carbon monoxide, carbonates and carbides are considered to be inorganic substances. This is because they have totally different properties than organic compounds. Organic compounds play a vital role in the bodies of living things. Products of industrial organic chemistry such as plastics, rubber, synthetic fibers, paints, glues, varnishes, artificial sweeteners and flavors, drugs, dyes, soaps and detergents etc. are important part of modern life. In addition, the energy on which we rely heavily is based mostly on organic materials found in coal, petroleum and natural gas. The Chemistry of carbon compounds pervades every aspect of our lives. We use thousands of carbon compounds every day. They are carrying out important chemical reactions within our bodies. Many of them are so vital that we cannot live without them. A detailed study of organic compounds confirms that carbon is their essential constituent in combination with H, O, N, S, P and halogens. They may also (rarely) contain metal atoms. Organic compounds are defined as the hydrocarbons and their derivatives. (See section 11.4 and Chapter 12) Carbon has four bonding electrons in its valence shell. Carbon therefore forms four bonds with other atoms. The Chemical diversity of organic compounds arises from carbon's ability to bond to each other to form long chains, branched chains and rings. This self-linking ability of carbon is called catenation. There appears to be almost no limit to the number of different structures that carbon can form. (See 11.1.6). No other element can compete with carbon in this regard. Silicon and few other elements can form chains, but only short one. Carbon chains may contain thousands of carbon atoms. For these reasons carbon forms almost infinite number of molecules of various sizes, shapes and structures. Another reason for the large number of organic compounds is the phenomenon of isomerism. The compounds that have same molecular formula but different arrangement of atoms in their molecules are called isomers. This phenomenon is called isomerism. For example two compounds have molecular formula C4H10 CH3-CH2—CH2—CH3 *n Butane* CH3-CH-CH3 *iso - Butane* What is the molecular formula of the following compounds? CH3-CH2—CH2—CH2—CH3 *n Pentane* CH3-CH————CH2—CH3 *iso - Pentane* CH3 C-CH3 *neo - Pentane* A teacher may give examples of petrol, kerosene, diesel, mobile oil as hydrocarbons. ## Organic Compounds with Functional Groups This means three compounds have molecular formula C5H12. As the number of carbon atoms in an organic compound increases, the number of possible isomers also increase. What is the number of isomers in pentane? Hexane has five isomers. Carbon can also form stable single and multiple bonds with other atoms like oxygen, nitrogen and sulphur. Carbon can also make multiple bonds to itself i.e. c=c,c≡c,c=o,c=n etc. This further increase the number of organic compounds. In fact, many common groups of atoms can occur within organic molecules. These groups are called functional group. (See 11.4). That is why of more than 20 million known chemical compounds; over 95% are compounds of carbon. Millions of organic compounds are already known and new ones are being discovered every day. In fact many common groups of atoms can occur within organic molecules. These groups are called functional groups. (See 11.5). ## Properties of Organic Compounds Most of them come from living things or from the things that were once living. Organic compounds are generally covalent in nature. They may have polar or non-polar bonds. Carbon is the main constituent of organic compounds. Hydrogen is also frequently present in organic compounds. Other elements like oxygen, nitrogen, sulphur, phosphorous and halogens are present in many organic compounds. Generally organic compounds are volatile. So they have low melting and boiling points. Organic compounds are mostly non-polar in nature therefore they are soluble in organic solvents such as ether, benzene, carbon disulphide etc. Polar Organic Compounds are soluble in alcohols such as methyl alcohol and ethyl alcohol. There exists a close relationship between different organic compounds. This similarity in behavior has made the study of millions of organic compounds easier. They can be classified into few families. A series of related compounds in which any two adjacent molecules differ by -CH2- group is called homologous series. ## Organic Compounds as Derivatives of Hydrocarbons Organic compounds are generally less stable than inorganic compounds. Due to covalent bonding in them, their reaction rates are often slow. Frequently more than one organic compounds are represented by the same molecular formula. However, they have different properties. They have different structural formulas. For example, two organic compounds have the molecular formula C2H6O. they have different arrangements of atoms. H H H- C- но-о H H *Ethanol* H H H -C C H H H *Dimethy ether* These formulas clearly show that the atoms are bonded to one another differently. In ethanol, the oxygen atom is bonded to only one carbon atom and a hydrogen atom. Whereas in dimethyl ether, the oxygen atom is bonded to two carbon atoms. A formula that describes the arrangement of atoms in a molecule is called as structural formula. The simple alkanes are straight-chain hydrocarbons. First three members of alkanes have following structural formulas. H H H H H H H-C H-C C H H-C C C-H H *Methane* H H *Ethane* H H H *Propane* The condensed structural formulas of these alkanes are CH4 CH3CH3 CH3CH2CH3, , . The corresponding molecular formulas are CH4,C2H6,C3H8respectively A condensed formula is a structural formula that uses established abbreviation for various groups of chain. In condensed structural formula, we list the main chain carbon atoms and the hydrogen atoms attached to them in the sequence in which they appear in the naming system. For instance, H H C Shown as —CH3 (Methyl) H H C as —CH2— (Methylene) H H H H H-C CCH H H H CH3-CH2-CH3 Table 11.1 shows the condensed structural formulas of some alkanes. | Name | Molecular Formula | Condensed Formula | | ---------- | ------------------- | --------------------------------------- | | Butane | C4H10 | CH3CH2CH2CH3 | | Pentane | C5H12 | CH3CH2CH2CH2CH3 | | Hexane | C6H14 | CH3CH2CH2CH2CH2CH3 | | Heptane | C7H16 | CH3CH2CH2CH2CH2CH2CH3 | | Octane | C8H18 | CH3CH2CH2CH2CH2CH2CH2CH3 | | Nonane | C9H20 | CH3CH2CH2CH2CH2CH2CH2CH2CH3 | | Decane | C10H22 | CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 | Give the molecular formula, the structural formula and the condensed structural formula for pentane. i) The stem pent –means five carbon atoms. ii) The ending -ane indicates an alkane. iii) Write a string or chain of five carbon atoms. iv) Attach hydrogen atoms to the carbons to give each carbon atom four bonds. This requires three hydrogen atoms on each end carbon and two each on others. v) For the condensed molecular formula, write each carbon atom's set of hydrogen atoms next to the carbon. vi) For molecular formula, simply count the carbon and hydrogen atoms or use the general formula CnH2n+2with n=5. C-C-C-C-C H H H H H H- C C C C H H H H H CH3—CH2—CH2—CH2—CH3 *C5H2x5+2 = C5H12* ## Structure & Nomenclature of Organic Compounds Give the molecular, structural and condensed structural formulas for (a) Butane (b) Hexane (c) Octane Hydrocarbons are compounds containing carbon and hydrogen only. Hydrocarbons whose carbon carbon bonds are all single bonds are called saturated. Saturated hydrocarbons are also called alkanes. In alkanes each carbon atom is bonded to four other atoms. Methane is the simplest alkane. Other examples are ethane, propane, butane etc. (See section 11.1.3 for more examples). The general formula of alkanes is *CnH2n+2*, where n is the number of carbon atoms. H H-C-H H *Methane* Hydrocarbons containing carbon-carbon multiple bonds are called unsaturated. Which of the following are unsaturated hydrocarbons? H Η Η Η c=c H H Η Η *Ethane* *Ethene* H-c=c-H *Ethyne* Unsaturated hydrocarbons are further divided into: (i) Alkenes. (ii) Alkynes. Unsaturated hydrocarbons containing at least one carbon-carbon double bond are called alkenes. They have general formula (H2SO4), for example ethene. Unsaturated hydrocarbons that have at least one carbon-carbon triple bond are called alkynes. They have general formula CnH2n-2, for example ethyne. Choose saturated and unsaturated compounds from the following. (i) CH3-CH2-CH3 (ii) CH3-CH=CH2 (ii) CH3-C≡CH (iv) CH2=CH-CH=CH2 An international body, the international union of pure and applied chemistry (IUPAC) has devised a system of naming organic compounds that depends on their structure. These names indicate the number of carbon atoms present in the organic compounds. We can easily recognize organic compound by its IUPAC name. Such names are also called systematic names. The key point in naming a straight chain alkane is that the name is based on the number of carbon atoms in the chain. The IUPAC name has two parts. The stem tells the number of carbon atoms in the chain. Table 11.2 shows these stems. | Stem | Number of C - atoms | | -------- | ------------------- | | Meth- | 1 | | Eth- | 2 | | Prop- | 3 | | But- | 4 | | Pent- | 5 | | Hex- | 6 | | Hept- | 7 | | Oct- | 8 | | Non- | 9 | | Dec- | 10 | Suffix is placed after the stem, it tells the class of compound. For alkane, the suffix “ane” is used. Suffix it indicates alkane Stem, it indicates no. of carbon atoms Write IUPAC names of the following compounds. (i) CH3-CH2-CH2- CH3 (ii) CH3- CH2- CH2- CH2-CH3 (i) Count number of carbon atoms in the chain and select stem for it. (ii) Add suffix ane to the stem. (i) No. of Carbon atoms 4 Stem - But Name: Butane (ii) No. of Carbon atoms 5 Stem - Pent Name: Pentane Write IUPAC names of the following alkanes. (i) CH3-CH2-CH2-CH2-CH2-CH3 (ii) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3 (iii) CIH3-CH2-CH2-CH2-CH2- C112- C113 (iv) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 (v) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3 The major commercial sources of alkanes are coal, natural gas, petroleum, and living organisms. ## Functional Groups Coal is a source of many organic compounds. When coal is heated in the absence of air at high temperature, it is converted into coal gas, coal tar and coke. This process is called destructive distillation. Coal is also used as solid fuel. Coal gas contains methane, hydrogen and carbon monoxide gases. It is mainly used as a fuel in industry. Coal tar is a source of many organic compounds such as benzene and its derivatives. These compounds can be separated by fractional distillation. These are very useful substances in synthetic organic chemistry. These are used to synthesize plastics, dyes, fibers, drugs, paints, varnishes etc. The residue left behind called pitch is used to metal roads and roofs. Natural gas is a mixture of low boiling hydrocarbons. Natural gas is mostly methane. It also contains smaller amounts of ethane, propane and butane. Petroleum contains a wide variety of alkanes including those having very long chains. On fractional distillation petroleum separates into various hydrocarbon components, known as fractions. Can you name these fractions? Each fraction is not a pure compound but a mixture of different compounds that boil in a certain range of temperature. (See section 16.4) Many important organic compounds such as proteins, fats, carbohydrates, vitamins, drugs and medicines are obtained from plants and animals. Over ten million organic compounds have been prepared in the laboratories. They are being used in medicines, cosmetics, paints, plastics, fertilizer, detergents, etc. - Natural gas and petroleum are used primarily as fuels (see figure 16.9). These are also used as starting materials for the productions of variety of organic compounds. - Propane and butane which are gases obtained from natural gas are widely available as liquids in fuel cylinders (LPG). - Ethylene is the major starting material for the manufacture of organic chemicals and products such as polyethylene (plastic), ethyl alcohol, acetic acid and ethylene glycol called antifreeze. - Acetylene is widely used in the oxy-acetylene welding and cutting metals. Acetylene is also used in the preparation of polymers like PVC (polyvinyl chloride), polyvinyl acetate, synthetic rubber, nylon etc. - Acetylene is used for artificial ripening of fruits. - Compounds of phenol help to ensure antiseptic conditions in hospital operating rooms. - Methanol is used as a solvent for fats, oils, paints and varnishes. - Many organic compounds are used in the manufacturing of drugs, dyes, cosmetics, detergents and soaps, nylon, emulsions and paints etc. 1. List the names of major sources of alkanes. 2. What is natural gas? 3. Write some uses of acetylene. Teacher may show different organic compounds to students. ## Alkyl Radicals Recall that an alkane is a hydrocarbon containing only single bonds and have general formula *CnH2n + 2*. An alkyl radical is a group of atoms obtained by removing one hydrogen atom from an alkane. Alkyl radicals are represented by the symbol R. Convert following alkanes into alkyl radical. (i) Methane (ii) Ethane (i) Write condensed structure formula for the given compound. (ii) Remove a hydrogen atom from the terminal carbon atom. (iii) Write name of the radical by removing ending -ane of alkane by -yl (i) CH4 *Methane* CH3 *Methyl* (ii) CH3CH3 *Ethane* CH3CH2- *Ethyl* What is the difference between methane and methyl radical? Which one contain a free valency? Alkanes containing more than two carbon atoms form more than one alkyl groups. For instance, propane forms two alkyl groups or radicals. The group obtained by removing terminal hydrogen atom is called n-propyl and that obtained by removing H-atom from central carbon atom is called iso-propyl group. CH3-CH2-CH2- *(n-propyl)* CH3-CH2-CH3 CH3-CH – CH3 *(iso-propyl)* Derive alkyl radicals from the following alkanes. a. Ethane b. Butane c. Propane ## Classifying Organic Compounds- Open Chain, Closed Chain There are millions of organic compounds. It is not possible to study each compound individually. To make the study easy, they are classified into various groups and subgroups. It is helpful to pick out these compounds which have similar structure. So you will learn here, the classification of organic compounds on the basis of carbon skeleton. They are broadly classified into two main groups. (i) Open chain compounds or Acyclic compounds. (ii) Closed chain or Cyclic Compounds. **Do you know?** Alkyl radical contains one less hydrogen than its parent alkane. Open chain compounds contain an open chain of carbon atoms. For instance CH3-CH2-CH3 *Propane* CH3-CH2-CH-CH3 *Butane* CH3 CH3-CH2—CH2—CH3 CH3-CH-CH3 *Butane* *iso-Butane* CH3 *iso - Pentane* Is the compound having following structure an open chain compound? CH2-CH2 CH2-CH2 Open chain compounds may be either straight-chain or branched-chain. Those compounds which contain any number of carbon atoms joined one after the other in a chain or row are called straight – chain compounds. CH3-CH2-CH3 *Propane* CH3-CH2-CH2-CH3 *Butane* CH3—CH2—CH2—CH2—CH3 *Pentane* Teacher may tell students that Sui Gas is mainly methane containing small amount of ethane, propane and butane. Those compounds which contain carbon atoms on the sides of chain are called branched chain compounds. Which of the following is a branched chain compound? CH3 CH3—C—CH3 CH3 *neo-Pentae* CH3-CH2—CH2—CH3 *Butane* CH3-CH-CH3 CH3 *iso-Butane* Open chain compound are also called alicyclic compounds Organic compounds which contain rings of atoms are called closed chain or cyclic compounds. For example CH2 CH2-CH2 H2C CH2 CH2-CH2 *Cyclopropane* *Cyclobutane* CH2 CH H2C CH2 HC CH H2C CH2 HC CH CH2 CH or *Cyclo hexane* *Benzene* Cyclic compounds which contain rings of carbon atoms are called homocyclic or carbocyclic compounds. Which of the above cyclic compounds are carbocyclic? Cyclic compounds that contain one or more atoms other than carbon atoms in the ring are called heterocyclic compounds e.g. N *Pyridine* S *Furan* *Thiophene* ## Functional Groups- Definition & Types A to E are the structural formulas of some organic compounds. H H H H H H H H C C C C-H C C C-H H H-C H H H H H *A* H *B* H CH2 I I H2C CH2 H- C C -C-H CH CH *C* H OH H *D* H H H H H- C C C H HH-C-H Η H *E* (i) A branched chain compound. (ii) A cyclic compound. (iii) Two straight chain compounds. The vast majority of organic compounds contain elements in addition to carbon and hydrogen. Most of these compounds are considered as derivatives of hydrocarbons. This means that they are basically hydrocarbons but they have additional atom or groups of atoms in place of one or more hydrogen atoms called functional groups. In many simple molecules, a functional group is attached to an alkyl group. An atom or groups of atoms that give a family of organic compounds its characteristic chemical and physical properties is called a functional group. What is the difference in the following compounds? CH4 *Methane* H3COH *Methyl alcohol* H3C-CI *Methyl Chloride* The common functional groups are listed in the table 11.2. The study of organic chemistry is organized around functional groups. Each functional group defines a family of organic compounds. Although, there are millions of organic compounds, yet there are only a handful of functional groups. So functional groups make the study of millions of organic compounds easier. | Name of class | Functional group | General formula | | --------------- | ------------------ | ---------------- | | Alkane | None | R-H | | Alkane | | R-C-R' R" | | Alkyne | | R-C≡C-R' | | Alcohol | -O-H | R-O-H | | Ether | -O- | R-O-R' | | Aldehyde | -C-H | R-C-H | | Ketone | | R-C-R' | | Amine | -N- | R-N-H R-N-R' | | Carboxylic acid | -COOH | R-COOH | | Ester | -COO- | R-COO-R' | Each functional group exhibits character ==End of OCR for page 22==