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How many primary (1 deg), secondary (2 deg), and tertiary (3 deg) carbon atoms does 1,3,5-trimethylcyclohexane possess?

1. 3, 6, 0
2. 3, 4, 2
3. 0, 3, 6
4. 3, 3, 3

Correct answer: 3, 4, 2

Solution

1,3,5-Trimethylcyclohexane has 3 methyl groups (each a primary carbon) attached to ring positions 1, 3, 5 (each a tertiary carbon bonded to 3 C's). Ring positions 2, 4, 6 are each bonded to 2 ring carbons and 1 H2 (secondary). Wait, ring position 2 is bonded to C1, C3 (two carbons) = secondary (2 C neighbors); there are 3 such positions (2,4,6) = 3 secondary ring C. But that gives 3 primary + 3 secondary + 3 tertiary = 9... but ring has 6 C and 3 methyl = 9 total C. So: 1 deg = 3, 2 deg = 3, 3 deg = 3 → option D. But wait, each ring CH2 at 2,4,6 is bonded to 2 adjacent ring carbons → that is 2 carbon neighbors → secondary. There are 3 such positions. Hmm, actually positions 2, 4, 6 each have TWO ring-carbon neighbors, making them secondary. So answer should be 3,3,3.

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