Alcohols: nomenclature, isomerism, preparation

Compounds formed when a hydrogen atom of a hydrocarbon is replaced by a hydroxyl (–OH) group are alcohols; by the number of –OH groups they are mono-, di- and polyhydric. The general formula of saturated monohydric alcohols is CₙH₂ₙ₊₁OH. The rational name is the radical name plus “alcohol” (methyl alcohol, ethyl alcohol); the systematic name is the alkane name plus “-ol” with the number of the carbon bearing –OH: methanol, ethanol, propanol-1, propanol-2. Numbering starts at the end nearer –OH. If –OH is on a primary carbon the alcohol is primary, on a secondary carbon secondary, on a tertiary carbon tertiary (butanol-1, butanol-2, 2-methylpropanol-2). Isomerism: chain, position of –OH and interclass — alcohols and ethers: C₂H₅OH and CH₃–O–CH₃. Preparation: hydrolysis of haloalkanes with aqueous KOH (C₂H₅Br + KOH → C₂H₅OH + KBr), hydration of alkenes following Markovnikov’s rule (CH₂=CH–CH₃ + H₂O → CH₃–CH(OH)–CH₃), hydrolysis of esters, hydrogenation of aldehydes and ketones, and industrially methanol from synthesis gas: CO + 2H₂ → CH₃OH.