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Organic Chemistry - Some Basic Principles and Techniques
IUPAC Nomenclature of Alkanes
1 question from 1 paper, each with its answer.
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- of Organic Chemistry - Some Basic Principles and Techniques
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Concepts tested
- Longest chain, lowest locants, alphabetical order
All Questions
2003 AIPMT 1 question
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IUPAC name of the compound given below is :
Step 1: Find the longest carbon chain. The longest chain has eight carbons, so the parent alkane is octane.
Step 2: Number the chain from the end that gives the lowest locants to the substituents. Numbering from the end nearer the branches gives a methyl group at C-3 and an ethyl group at C-4 (locant set 3, 4). Numbering from the other end would give 5, 6, which is higher.
Step 3: Write the substituents in alphabetical order (ethyl before methyl), irrespective of their locant numbers.
So the name is 4-Ethyl-3-methyloctane.
'3-Methyl-4-ethyloctane' has the correct numbers but wrong alphabetical order; '5-ethyl-6-methyloctane' uses higher locants; 'diethylheptane' does not use the longest chain.