Question

Explain why each of the following names is incorrect

Answer 1

Explanation:

Alkanes are the hydrocarbons in which single bonds are present between the carbon atoms

The suffix for alkane hydrocarbons used is '-ane'. The rules to write the nomenclature of alkanes follows:

• Select the longest possible continuous carbon chain and it will be the parent chain
• Numbering is done as such that the alkyl substituents are given the lowest number
• If different alkyl groups are present, they are written in an alphabetical order irrespective of their position in the carbon chain
• If two or more similar alkyl groups are present, the words, di, tri, tetra, and so on are used to specify the number of times alkyl groups appear
• If two or more alkyl groups are present and the branching occurs, the numbering is done which gives the minimum possible number to all the substituents

For the given options:

(a) 2,2-Dimethyl-6-ethylheptane

The longest possible carbon chain has 8 carbon atoms (prefix used is 'oct-') and not 7(prefix used is 'hept-').

Thus, the correct IUPAC name will be 2,2,6-trimethyloctane.

(b) 4-Ethyl-5,5-dimethylpentane

The longest possible carbon chain has 6 carbon atoms (prefix used is 'hex-') and not 5(prefix used is 'pent-').

Thus, the correct IUPAC name will be 4-isopropylhexane.

(c) 3-Ethyl-4,4-dimethylhexane

The substituents are not given the minimum possible number. Total sum of the number in original compound = [4 + 4 + 3] = 11

But, if both the methyl groups are placed at 3rd position, then total sum of the number = [3 + 3 + 4] = 10

Thus, the correct IUPAC name will be 4-ethyl-3,3-dimethylhexane

(d) 5,5,6-Trimethyloctane

The substituents are not given the minimum possible number. Total sum of the number in original compound = [5 + 5 + 6] = 16

But, if both the methyl groups are placed at 3rd position and 4th position, then total sum of the number = [3 + 3 + 4] = 10

Thus, the correct IUPAC name will be 3,3,4-trimethyloctane

(e) 2-Isopropyl-4-methylheptane

The longest possible carbon chain has 8 carbon atoms (prefix used is 'oct-') and not 7 (prefix used is 'hept-').

Thus, the correct IUPAC name will be 2,3,5-trimethyloctane

The structures of the compounds are attached below.