Chains, Branches and Rings of Hydrocarbon

Chains, Branches and Rings of Hydrocarbon


In the earlier section, we mentioned the carbon compounds methane, ethane and propane, containing respectively 1, 2 and 3 carbon atoms. Such ‘chains’ of carbon atoms can contain many more carbon atoms.
The names and structures of six of these are given in Table .

Table – Formulae and structures of saturated compounds of carbon and hydrogen

But, let us take another look at butane. If we make the carbon ‘skeleton’ with four carbon atoms,

C—C—C—C

Figure – (a) carbon-skeletons

Filling the remaining valencies with hydrogen gives us –

Figure – (b) Complete molecules for two structures with formula C4H10

We see that both these structures have the same formula C4H10. Such compounds with identical molecular formulas but different structures are called structural isomers.
In addition to straight and branched carbon chains, some compounds have carbon atoms arranged in the form of a ring. For example, cyclohexane has the formula C6H12 and the following structure –

Figure – Structure of cyclohexane (a) carbon skeleton (b) complete molecule

Straight chain, branched chain and cyclic carbon compounds, all may be saturated or unsaturated. For example, benzene, C6H6, has the following structure –

Figure – Structure of benzene

All these carbon compounds which contain only carbon and hydrogen are called hydrocarbons. Among these, the saturated hydrocarbons are called alkanes. The unsaturated hydrocarbons which contain one or more double bonds are called alkenes. Those containing one or more triple bonds are called alkynes.

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