primary alcohols

Meaning: In a primary (1°) alcohol, the carbon bearing the –OH is attached to one other carbon, written R–CH₂–OH. Ethanol, 1-propanol and 2-methyl-1-propanol are examples; methanol is usually grouped with them. That carbon still has two hydrogens, so it can be oxidized in stages. The –OH is a poor leaving group, so it is first protonated or converted to a tosylate or halide. Primary carbons then typically react by SN2, because they are unhindered and a primary carbocation is unstable.

On the MCAT: Expect oxidation questions. PCC stops at the aldehyde. Stronger oxidants (CrO₃ with H₂SO₄, K₂Cr₂O₇, KMnO₄) usually carry the reaction on to the carboxylic acid. Secondary alcohols give ketones, and tertiary alcohols resist oxidation because the carbinol carbon has no hydrogen. The reverse is also tested: LiAlH₄ reduces aldehydes, esters and carboxylic acids to primary alcohols, while NaBH₄ reduces aldehydes but typically not carboxylic acids. Hydrogen bonding gives primary alcohols higher boiling points than alkanes or ethers of similar mass.

Common confusion: "Primary" describes the carbon holding the –OH, not the length of the chain or the position of the –OH on it. Count the carbons attached to the carbinol carbon. Branching elsewhere does not change the class, so 2-methyl-1-propanol is still primary.