Which of the following is NOT a possible isomer of hexane?

Correct option is A

(a) 2-ethyl pentane

The correct answer is 2-ethyl pentane because it is not a possible isomer of hexane (C6H14). Let's break down the reasoning:

• Hexane (C6H14) has six carbon atoms, and isomers of hexane must maintain this number of carbon atoms.
• 2-ethylpentane has seven carbon atoms, not six. The name 2-ethylpentane suggests a five-carbon chain (pentane) with an ethyl group attached at the second carbon, resulting in a molecule with seven carbon atoms, not six. Hence, it cannot be an isomer of hexane.

The other options are valid isomers of hexane:

• 3-methylpentane is a six-carbon chain with a methyl group attached to the third carbon.
• 2-methylpentane is a six-carbon chain with a methyl group attached to the second carbon.
• 2, 2-dimethylbutane is a six-carbon molecule with two methyl groups attached to the second carbon of a four-carbon chain.

Therefore, 2-ethyl pentane is not a valid isomer of hexane.

Important Key Points:

1. The principle of isomerism requires that the molecular formula remains the same while the structure differs.
2. Structural isomers of a molecule share the same molecular formula but differ in the connectivity of atoms.
3. IUPAC nomenclature helps in naming organic molecules based on the structure and functional groups present.

Knowledge Booster:

• Isomerism in organic chemistry is divided into two types: structural isomerism (where the connectivity of atoms changes) and stereoisomerism (where the connectivity remains the same, but the arrangement in space differs).