Unit After studying this unit, you will be able to • name hydrocarbons according to IUPAC system of nomenclature; • recognise and write structures o f i s o m e r s o f a l k a n e s , alkenes, alkynes and aromatic hydrocarbons; • learn about various methods of preparation of hydrocarbons; • distinguish between alkanes, alkenes, alkynes and aromatic hydrocarbons on the basis of physical and chemical properties; • draw and differentiate between various conformations of ethane; • a p p r e c i a t e t h e r o l e o f hydrocarbons as sources of energy and for other industrial applications; • pr edict the for mation of the addition products of unsymmetrical alkenes and alkynes on the basis of electronic mechanism; • comprehend the structure of benzene, explain aromaticity and understand mechanism of electrophilic substitution reactions of benzene; • predict the directive influence of substituents in monosubstituted benzene ring; • learn about carcinogenicity and toxicity. The term ‘hydrocarbon’ is self-explanatory which means compounds of carbon and hydrogen only. Hydrocarbons play a key role in our daily life. You must be familiar with the terms ‘LPG’ and ‘CNG’ used as fuels.
LPG is the abbreviated form of liquified petroleum gas whereas CNG stands for compressed natural gas. Another term ‘LNG’ (liquified natural gas) is also in news these days. This is also a fuel and is obtained by liquifaction of natural gas. Petrol, diesel and kerosene oil are obtained by the fractional distillation of petroleum found under the earth’s crust.
Coal gas is obtained by the destructive distillation of coal. Natural gas is found in upper strata during drilling of oil wells. The gas after compression is known as compressed natural gas. LPG is used as a domestic fuel with the least pollution.
Kerosene oil is also used as a domestic fuel but it causes some pollution. Automobiles need fuels like petrol, diesel and CNG. Petrol and CNG operated automobiles cause less pollution. All these fuels contain mixture of hydrocarbons, which are sources of energy.
Hydrocarbons are