# 12.5     Which of the following represents the correct IUPAC name for the compounds concerned?                 (a) 2,2-Dimethylpentane or 2-Dimethylpentane                 (b) 2,4,7- Trimethyloctane or 2,5,7-Trimethyloctane                 (c) 2-Chloro-4-methylpentane or 4-Chloro-2-methylpentane                 (d) But-3-yn-1-ol or But-4-ol-1-yne.

(a) The prefix $di$ in the IUPAC nomenclature is indicating two identical substituent group in the parent chain. Since two methyl group present at $C_2$ of the parent chain. So, the correct IUPAC name is 2, 2-dimethylpentane.

(b) In IUPAC nomenclature the sum of locant number should be minimum. Here the sum of 2,4,7 (=13)is less than the sum of 2, 5, 7 (=14). Thus the correct IUPAC name is 2,4,7- Trimethyloctane

(c) In IUPAC nomenclature, if the substituent group acquires the equivalent position of the parent chain then the lower number is given to one that comes first in alphabetical order. Hence 2-Chloro-4-methyl pentane is the correct IUPAC name of the compound.

(d) If the two functional groups are present in the parent chain then the suffix of the IUPAC name depends on the principal functional group. Here alcohol is the principal function group so the suffix should be $-ol$ and alkyne group considered as a substituent group. Therefore the correct IUPAC name of the compound is But-3-yn-1-ol

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