Question

Which of the following represents the correct structure of 3-Ethyl cyclohexane carbaldehyde?

• A. Option 1
• B. Option 2
• C. Option 3
• D. Option 4

Hint:

For cyclic aldehydes, the suffix “carbaldehyde” is used because the aldehyde carbon is not a part of the ring. Numbering starts from the ring carbon attached to the \(-CHO\) group.

Answer 1

The Correct Option is B

Concept: In IUPAC nomenclature, when an aldehyde group \((-CHO)\) is attached directly to a ring, the suffix carbaldehyde is used. For naming substituted cyclohexane carbaldehydes:

• The carbon attached to the \(-CHO\) group is numbered as carbon-1.
• Numbering proceeds around the ring so as to give the substituent the lowest possible locant.
• The aldehyde carbon itself is not included in the ring numbering.

Step 1: Identify the parent structure.
The parent compound is \[ \text{Cyclohexane carbaldehyde} \] Therefore the ring carbon attached to the \(-CHO\) group becomes carbon-1.

Step 2: Locate the ethyl substituent.
The name given is \[ \text{3-Ethyl cyclohexane carbaldehyde} \] Hence the ethyl group must be present at carbon-3 of the cyclohexane ring when numbering starts from the carbon attached to the aldehyde group.

Step 3: Check the given structures.

• Option (1) contains a \(-CH_2CHO\) side chain, therefore it is not a carbaldehyde.
• Option (3) contains an aromatic ring representation and does not correspond to cyclohexane carbaldehyde.
• Option (4) contains a double bond in the ring and is not cyclohexane.
• Option (2) has a cyclohexane ring, a directly attached \(-CHO\) group, and an ethyl group at the third carbon.

Hence the correct structure is \[ \boxed{\text{Option (2)}} \]