Question

(a) Explain the term 'isomers'. Give one example of isomers.
(b) Write (i) structural formula, and (ii) electron-dot structure, of any one isomer of n-heptane (C₇H₁₆).
(c) Write IUPAC name of the compound having the formula n-C₄H₁₀.
(d) Give the IUPAC names for the following:
(i) Figure
(ii) Figure
(iii) Figure
(iv) Figure

Answer 1

(a) Isomers: Isomers are compounds with the same molecular formula but different arrangements of carbon atoms in them. The existence of two or more organic compounds with the same molecular formula but different arrangement of carbon atoms is called isomerism. Isomerism can only exist in hydrocarbons comprising 4 or more carbon atoms.
An example of an isomer is the compound Butane (C₄H₁₀)​. As the number of carbon atoms are four, two isomers of butane are possible, and they are n-butane (normal butane with a straight chain arrangement) and iso-butane (three carbon atoms put in a straight chain, and the fourth carbon atom is joined in the side chain to form a different structure).
The structural formula for the isomers of butane are as follows:

(b) (i) Heptane (C₇H₁₆) has 7 carbon atoms in its molecule. An isomer other than n-heptane will be 2-methylhexane.The structural formula is shown below :


(ii) The electronic dot structure is as follows:

(c) The IUPAC name of n-C₄H₁₀ is butane.
This is because the compound is a saturated hydrocarbon and has 4 carbon atoms in its molecule. If it has four carbon atoms in a single chain, it is represented by the word "but", and as it comprises all single bonds, it is represented by the ending "ane". Again, as the carbon atoms are in a single continuous chain, it is represented by n-Butane (where, n is normal).

(d) (i) 2-methylpropane

(ii) 2-methylbutane

(iii) Propene

(iv) Propyne