In an alcohol, what is the difference between primary, secondary, and tertiary in terms of the attached carbon?

In an alcohol, what is the difference between primary, secondary, and tertiary in terms of the attached carbon?

• A. Primary: carbon bearing OH attached to three other carbons; secondary to two; tertiary to one.
• B. Secondary: carbon bearing OH attached to one other carbon; primary to two; tertiary to three.
• C. Primary: OH on a carbon attached to four other carbons.
• D. Primary: OH on a carbon with no hydrogens.

Answer: (B)

The thing being tested is how many carbon neighbors the carbon bearing the hydroxyl group has. That count defines the classification: primary means the OH-bearing carbon is attached to one other carbon, secondary means it’s attached to two carbons, and tertiary means it’s attached to three carbons. In other words, you look at the carbon that bears the OH and count how many carbons are bonded to it. From that viewpoint, a primary alcohol has two hydrogens on the carbon with the OH, a secondary alcohol has one hydrogen, and a tertiary alcohol has no hydrogens on that carbon because it’s bonded to three other carbons. The other options describe scenarios that don’t match how these alcohols are actually structured (such as a carbon with OH bonded to four carbons, or a carbon with no hydrogens), so the standard description is the one that counts the carbon neighbors of the OH-bearing carbon.

The thing being tested is how many carbon neighbors the carbon bearing the hydroxyl group has. That count defines the classification: primary means the OH-bearing carbon is attached to one other carbon, secondary means it’s attached to two carbons, and tertiary means it’s attached to three carbons. In other words, you look at the carbon that bears the OH and count how many carbons are bonded to it.

From that viewpoint, a primary alcohol has two hydrogens on the carbon with the OH, a secondary alcohol has one hydrogen, and a tertiary alcohol has no hydrogens on that carbon because it’s bonded to three other carbons. The other options describe scenarios that don’t match how these alcohols are actually structured (such as a carbon with OH bonded to four carbons, or a carbon with no hydrogens), so the standard description is the one that counts the carbon neighbors of the OH-bearing carbon.