Hydrocarbons

Introduction

Hydrocarbons are organic compounds composed exclusively of carbon and hydrogen atoms. They form the fundamental backbone of organic chemistry and are pivotal in various chemical industries and energy sectors. Hydrocarbons are primarily derived from natural sources such as petroleum and natural gas. These compounds serve as the main source of fuel in daily life, including LPG (liquified petroleum gas), CNG (compressed natural gas), and LNG (liquified natural gas). Understanding hydrocarbons is essential because they are involved in the production of fuels, lubricants, and many synthetic materials. The term 'hydrocarbon' itself indicates compounds containing only hydrogen and carbon atoms. The study of hydrocarbons includes their classification, nomenclature, preparation, physical and chemical properties, and their significance in real-world applications. **Table on page 1 (1×2)** | HYDROCARBONS Hydrocarbons are the important sources of energy. After studying this unit, you will be able to š name hydrocarbons according to The term ‘hydrocarbon’ is self-explanatory which mea IUPAC system of nomenclature; compounds of carbon and hydrogen only. Hydrocarbo š recognise and write structures play a key role in our daily life. You must be famili o f i s o m e r s o f a l k a n e s , with the terms ‘LPG’ and ‘CNG’ used as fuels. LPG is t alkenes, alkynes and aromatic abbreviated form of liquified petroleum gas whereas CN hydrocarbons; stands for compressed natural gas. Another term ‘LN š learn about various methods of (liquified natural gas) is also in news these days. This preparation of hydrocarbons; also a fuel and is obtained by liquifaction of natural ga š distinguish between alkanes, alkenes, alkynes and aromatic Petrol, diesel and kerosene oil are obtained by the fraction hydrocarbons on the basis of distillation of petroleum found under the earth’s cru physical and chemical properties; Coal gas is obtained by the destructive distillation š draw and differentiate between coal. Natural gas is found in upper strata during drilli various conformations of ethane; of oil wells. The gas after compression is known š a p p r e c i a t e t h e r o l e o f compressed natural gas. LPG is used as a domestic fu hydrocarbons as sources of with the least pollution. Kerosene oil is also used as energy and for other industrial domestic fuel but it causes some pollution. Automobil applications; need fuels like petrol, diesel and CNG. Petrol and CN š pr edict the for mation of operated automobiles cause less pollution. All these fue the addition products of contain mixture of hydrocarbons, which are sources unsymmetrical alkenes and alkynes on the basis of electronic energy. Hydrocarbons are also used for the manufactu mechanism; of polymers like polythene, polypropene, polystyrene et š comprehend the structure of Higher hydrocarbons are used as solvents for paints. Th benzene, explain aromaticity are also used as the starting materials for manufactu and understand mechanism of many dyes and drugs. Thus, you can well understa of electrophilic substitution the importance of hydrocarbons in your daily life. In th reactions of benzene; unit, you will learn more about hydrocarbons. š predict the directive influence of | | | --- | --- | | | ns ns ar he G G’ is s. al st. of ng as el a es G ls of re c. ey re nd is | **Table on page 5 (4×2)** | | Structure and IUPAC Name Remarks | | --- | --- | | | Lowest sum and 1 2 3 4 5 6 (a) CH – CH – CH – CH – CH – CH alphabetical 3 2 2 3 ( – (th\l –  – meth\lhe[ane arrangement Lowest sum and (b) 8CH – 7CH – 6CH – 5CH – 4CH – 3C – 2CH – 1CH alphabetical 3 2 2 2 3 arrangement (3,3-Diethyl-5-isopropyl-4-methyloctane) sec is not considered (c) 1CH –2CH –3CH –4CH–5CH–6CH –7CH –8CH –9CH –10CH 3 2 2 2 2 2 2 3 while arranging alphabetically; isopropyl is taken 5-sec– %ut\lisoSroS\ldecane as one word (d) 1CH –2CH –3CH –4CH –5CH–6CH –7CH –8CH –9CH 3 2 2 2 2 2 2 3 Further numbering to the substituents of the side chain (– 'imeth\lSroS\l nonane (e) 1CH – 2CH – 3CH – 4CH – 5CH – 6CH – 7CH 3 2 2 2 3 Alphabetical priority order –(th\l––meth\lheStane | | Lowest sum and (b) 8CH – 7CH – 6CH – 5CH – 4CH – 3C – 2CH – 1CH alphabetical 3 2 2 2 3 arrangement (3,3-Diethyl-5-isopropyl-4-methyloctane) sec is not considered (c) 1CH –2CH –3CH –4CH–5CH–6CH –7CH –8CH –9CH –10CH 3 2 2 2 2 2 2 3 while arranging alphabetically; isopropyl is taken 5-sec– %ut\lisoSroS\ldecane as one word (d) 1CH –2CH –3CH –4CH –5CH–6CH –7CH –8CH –9CH 3 2 2 2 2 2 2 3 Further numbering to the substituents of the side chain (– 'imeth\lSroS\l nonane (e) 1CH – 2CH – 3CH – 4CH – 5CH – 6CH – 7CH 3 2 2 2 3 Alphabetical priority order –(th\l––meth\lheStane important to write the correct structu Problem 9.3 from the given IUPAC name. To do this, fir Write IUPAC names of the following of all, the longest chain of carbon ato compounds : corresponding to the parent alkane is writte (i) (CH ) C CH C(CH ) 3 3 2 3 3 Then after numbering it, the substituents a (ii) (CH ) C(C H ) attached to the correct carbon atoms a 3 2 2 5 2 (iii tetra – tert-butylmethane finally valence of each carbon atom is satisfi by putting the correct number of hydrog Solution atoms. This can be clarified by writing t (i) 2, 2, 4, 4-Tetramethylpentane structure of eth\l –dimeth\lSentane (ii) 3, 3-Dimethylpentane the following steps : | Lowest sum and (b) 8CH – 7CH – 6CH – 5CH – 4CH – 3C – 2CH – 1CH alphabetical 3 2 2 2 3 arrangement (3,3-Diethyl-5-isopropyl-4-methyloctane) sec is not considered (c) 1CH –2CH –3CH –4CH–5CH–6CH –7CH –8CH –9CH –10CH 3 2 2 2 2 2 2 3 while arranging alphabetically; isopropyl is taken 5-sec– %ut\lisoSroS\ldecane as one word (d) 1CH –2CH –3CH –4CH –5CH–6CH –7CH –8CH –9CH 3 2 2 2 2 2 2 3 Further numbering to the substituents of the side chain (– 'imeth\lSroS\l nonane (e) 1CH – 2CH – 3CH – 4CH – 5CH – 6CH – 7CH 3 2 2 2 3 Alphabetical priority order –(th\l––meth\lheStane | | | Problem 9.3 Write IUPAC names of the following compounds : (i) (CH ) C CH C(CH ) 3 3 2 3 3 (ii) (CH ) C(C H ) 3 2 2 5 2 (iii tetra – tert-butylmethane Solution (i) 2, 2, 4, 4-Tetramethylpentane (ii) 3, 3-Dimethylpentane | | | (iii) 3,3-Di-tert-butyl -2, 2, 4, 4 - tetramethylpentane | **Table on page 20 (6×4)** | | | | | | --- | --- | --- | --- | | there are two Sossible structures for but\ne CH 3 (i) but-1-yne and (ii) but-2-yne. Since the Polypropene two compounds differ in their structur (9.54) due to the position of the triple bond, th Polymers are used for the manufacture of plastic are known as position isomers. In ho bags, squeeze bottles, refrigerator dishes, toys, many ways, you can construct the structu pipes, radio and T.V. cabinets etc. Polypropene for the next homologue i.e., the next alky is used for the manufacture of milk crates, with molecular formula C H ? Let us try 5 8 plastic buckets and other moulded articles. arrange five carbon atoms with a continuo Though these materials have now become chain and with a side chain. Following are t common, excessive use of polythene and possible structures : polypropylene is a matter of great concern for Structure IUPAC name all of us. 1 2 3 4 5 I. HC≡C– CH 2– CH 2– CH 3ent–\ne 3 9.4 ALKYNES 1 2 3 4 5 Like alkenes, alkynes are also unsaturated II. H C–C≡ C– CH – CH 3ent–\ne 3 2 3 hydrocarbons. They contain at least one triple 4 3 2 1 bond between two carbon atoms. The number III.H 3C–CH–C≡ CH 0eth\l but–\ne | of hydrogen atoms is still less in alkynes as CH compared to alkenes or alkanes. Their general 3 Structures I and II are position isome formula is C H . n n– and structures I and III or II and III are cha The first stable member of alkyne series isomers. is ethyne which is popularly known as acetylene. Acetylene is used for arc welding Problem 9.13 purposes in the form of oxyacetylene flame Write structures of different isomers obtained by mixing acetylene with oxygen corresponding to the 5th member of gas. Alkynes are starting materials for a large alkyne series. Also write IUPAC names of number of organic compounds. Hence, it all the isomers. What type of isomerism is interesting to study this class of organic is exhibited by different pairs of isomers? compounds. Solution 9.4.1 Nomenclature and Isomerism 5th member of alkyne has the molecular In common system, alkynes are named as formula C H . The possible isomers are: derivatives of acetylene. In IUPAC system, they 6 10 Table 9.2 Common and IUPAC Names of Alkynes (C H ) n 2n–2 Value of n Formula Structure Common name IUPAC name | | | | | | | Problem 9.13 Write structures of different isomers corresponding to the 5th member of alkyne series. Also write IUPAC names of all the isomers. What type of isomerism is exhibited by different pairs of isomers? Solution 5th member of alkyne has the molecular formula C H . The possible isomers are: 6 10 | | | | | | | | | Value of n Formula Structure Common name IUPAC name | | | | | | | | | | 2 C H H-C≡CH Acetylene Ethyne 2 2 3 C H CH -C≡CH Methylacetylene Propyne 3 4 3 4 C H CH CH -C≡CH Ethylacetylene But-1-yne 4 6 3 2 4 C H CH -C≡C-CH Dimethylacetylene But-2-yne 4 6 3 3 | | |

• Hydrocarbons consist solely of carbon and hydrogen atoms.
• They are the primary source of energy in daily life.
• Common fuels like LPG, CNG, and LNG are hydrocarbons.
• Hydrocarbons form the basis of organic chemistry.
• They are derived mainly from petroleum and natural gas.
• Understanding hydrocarbons aids in industrial and synthetic applications.
• 📌 Hydrocarbon: Organic compound containing only carbon and hydrogen atoms.
• 📌 LPG: Liquified Petroleum Gas, a hydrocarbon fuel.
• 📌 CNG: Compressed Natural Gas, mainly methane used as fuel.

Classification of Hydrocarbons

Hydrocarbons are broadly classified into two main categories: saturated and unsaturated hydrocarbons. Saturated hydrocarbons, known as alkanes, contain only single bonds between carbon atoms. These are also called paraffins and have the general formula CnH2n+2. Unsaturated hydrocarbons contain one or more multiple bonds (double or triple) between carbon atoms. They are further divided into alkenes (with one or more double bonds) and alkynes (with one or more triple bonds). Aromatic hydrocarbons form a special class characterized by the presence of benzene rings or related structures with delocalized π electrons, giving them unique stability. This classification helps in understanding their chemical reactivity and physical properties. The saturation level affects the types of reactions these hydrocarbons undergo, such as addition reactions in unsaturated hydrocarbons and substitution reactions in saturated ones.

• Hydrocarbons are classified as saturated (alkanes) and unsaturated (alkenes, alkynes).
• Alkanes have only single C–C bonds and follow the formula CnH2n+2.
• Alkenes contain at least one carbon-carbon double bond (C=C).
• Alkynes contain at least one carbon-carbon triple bond (C≡C).
• Aromatic hydrocarbons contain benzene rings with delocalized π electrons.
• Classification influences chemical reactivity and physical properties.
• 📌 Saturated Hydrocarbon: Hydrocarbon with only single bonds.
• 📌 Unsaturated Hydrocarbon: Hydrocarbon with one or more double or triple bonds.
• 📌 Alkane: Saturated hydrocarbon with single bonds.