Explain why each of the following names is incorrect
(a) 2,2-Dimethyl-6-ethylheptane
(b) 4-Ethyl-5,5-dimethylpentane
(c) 3-Ethyl-4,4-dimethylhexane
(d) 5,5,6-Trimethyloctane
(e) 2-Isopropyl-4-methylheptane

Question

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BatteringRam BatteringRam · Answer 1 · 2021-06-23T05:01:34+02:00

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.