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Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on the number of carbon atoms attached to the carbinol carbon. This classification determines their reactivity in oxidation, dehydration, substitution, and identification tests.
Key preparation methods: (1) Grignard synthesis — the most versatile: RMgX + HCHO gives 1° alcohol, RMgX + aldehyde gives 2°, RMgX + ketone gives 3°. (2) Hydroboration-oxidation — anti-Markovnikov, syn addition, gives 1° alcohol from terminal alkenes. (3) Acid-catalysed hydration — Markovnikov addition, gives 2°/3° alcohol. (4) Reduction — LiAlH4 reduces all carbonyl compounds (aldehydes, ketones, acids, esters) to alcohols; NaBH4 is milder, only reducing aldehydes and ketones.
The contrast between hydroboration (anti-Markovnikov) and acid hydration (Markovnikov) is a favourite JEE topic. The key distinction: BH3 adds to the less substituted carbon, while H+ adds to the more substituted (Markovnikov) to give the more stable carbocation.