Which of the following compounds is a secondary alkanol?

Analyze the question: We need the alkanol (alcohol) in which the carbon bearing the –OH group is a secondary carbon, meaning it is bonded to two other carbon atoms.

Concept: Alcohols are classified by the carbon holding the –OH group:

• Primary (1°): the C–OH carbon is attached to one other carbon (R–CH₂OH)
• Secondary (2°): the C–OH carbon is attached to two other carbons (R₂CHOH)
• Tertiary (3°): the C–OH carbon is attached to three other carbons (R₃COH)

Step-by-step check:

• A. Ethanol (CH₃CH₂OH): The C–OH carbon is attached to only one carbon (CH₃). Primary.
• B. 2-methylbutan-2-ol: The structure is CH₃–C(OH)(CH₃)–CH₂CH₃. The C–OH carbon is attached to three carbons (two CH₃ groups, one CH₂). Tertiary.
• C. 3-methylpentan-2-ol: The structure is CH₃–CH(OH)–CH(CH₃)–CH₂–CH₃. The C-2 carbon bearing the –OH is attached to C-1 and C-3, so two carbons, and it has one hydrogen. Secondary.
• D. Propan-1-ol (CH₃CH₂CH₂OH): The C–OH carbon is at the end of the chain, attached to one carbon. Primary.

Answer: Option C, 3-methylpentan-2-ol, is the secondary alkanol.

Tip: Look at the number in the name. If the –OH is on carbon 1 of a chain, it is usually primary. If it is on an inner carbon with a hydrogen still attached (such as -2-ol in a chain), it is secondary. If the same carbon also carries a methyl branch (like 2-methylbutan-2-ol), it is tertiary. Always count the carbons attached to the C–OH carbon.