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When both a functional group and a substituent are present in a chain, how is the numbering of carbon atoms decided?
APriority is given to the functional group
BPriority is given to the substituent
CNumbering always starts from the left end
DNumbering always starts from the longer branch
Answer & Solution
Correct answer: A. Priority is given to the functional group
1. Numbering begins at the end closest to the substituent or functional group to keep locants low.
2. The rules state that the direction of numbering must not always start from a fixed end, so left-end and longer-branch options are wrong.
3. When both a functional group and a substituent are present, the functional group is given priority for the lower locant.
4. Hence priority is given to the functional group.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit 11 "Carbon and its Compounds", p.167_
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