Consider the following alcohol: Identify tertiary carbon:

The correct answer is Option (3) → \(_bC\)

A carbon atom is called primary, secondary, tertiary or quaternary according to the number of other carbon atoms bonded to it: one, two, three or four. Counting the carbon neighbours of each labelled carbon in the structure:

• C_a (\( \ce{CH3} \)) — bonded to one carbon (C_b) ⇒ primary

• C_b (CH) — bonded to two C_a methyl carbons and to C_c, i.e. three carbons ⇒ tertiary

• C_c — bonded to C_b, C_e and two C_d carbons, i.e. four carbons ⇒ quaternary

• C_e (\( \ce{CH2} \)) — bonded to C_c and C_f ⇒ secondary

The only tertiary carbon is C_b.

Why the other options are incorrect

• Option (1) \(_aC\) — Incorrect. A methyl carbon bonded to one carbon only, so it is primary.

• Option (2) \(_eC\) — Incorrect. The \( \ce{CH2} \) carbon is bonded to two carbons, so it is secondary.

• Option (4) \(_cC\) — Incorrect. It carries no hydrogen and is bonded to four carbons, so it is quaternary, not tertiary.