Question

Which of the following represents the correct IUPAC name for the compounds concerned?
a) 2-Chloro-4-methyl pentane
b) 4-Chloro-2-methyl pentane

Answer 1

To identify the answer, we need to recall the IUPAC rules of Nomenclature for Alkanes. According to IUPAC nomenclature, there is a preference series of the groups attached to the parent chain. Also, the numbering of the parent chain carbon atoms is done accordingly.

Complete Step By Step Answer:
Here as we can see both the options a) 2-Chloro-4-methyl pentane b) 4-Chloro-2-methyl pentane have the same parent chain pentane. So, we have to find the correct numbering of the substituted functional groups.
According to the IUPAC priority list of the functional groups attached to the parent chain, halogens are above the methyl group. The more preferred group is numbered as such that it gets the smaller number in the parent chain. So, the halogen group i.e. chlorine will be given a smaller number than the methyl group.
Also, the groups attached to the parent chain are arranged in alphabetical order. So, Chloro would come before the methyl group. But, as the former is prioritized it is given the number two.
Therefore, the correct IUPAC name for the compound is 2-Chloro-4-methyl pentane.
Final answer: The correct answer is Option A- 2-Chloro-4-methyl pentane.

Note:
To find out the side from which we should start the numbering of the parent compound you must know the priority list of the functional groups. Remember that the sum of the numbers of the functional groups in a compound should be less than the other side.
The priority list of the functional group is as follows:
-COOH > -CHO > R-O-R > -OH > Halides > methyl.