Alcohols classified by the carbon bearing -OH: 1° alcohol — C bonded to only one other C (e.g., ethanol CH3CH2OH, n-propanol). 2° alcohol — C bonded to two other C's (e.g., isopropanol (CH3)2CHOH). 3° alcohol — C bonded to three other C's (e.g., tert-butanol (CH3)3COH). Methanol (CH3OH) is sometimes classified separately (no C-C bond on carbinol carbon). Classification critically determines: (1) oxidation products (1° -> aldehyde -> acid; 2° -> ketone; 3° resistant), (2) dehydration ease (3° > 2° > 1°), (3) substitution mechanism (1° = SN2, 3° = SN1), (4) Lucas test response (3° immediate, 2° 5 min, 1° slow).