Alcohols are named by replacing the -e suffix of the parent alkane with -ol. The position of the hydroxyl group is indicated by a number before the suffix. For alcohols with multiple hydroxyl groups, use suffixes like -diol or -triol.
2. Preparation of Alcohols★★☆☆☆⏱ 15 min
There are four common preparation routes for alcohols regularly tested in CIE exams:
Nucleophilic substitution (hydrolysis) of halogenoalkanes with aqueous sodium hydroxide
Electrophilic addition (hydration) of alkenes with steam and acid catalyst (industrial)
Reduction of aldehydes/ketones with $NaBH_4$ to 1°/2° alcohols
Anaerobic fermentation of glucose to produce ethanol
3. Key Reactions of Alcohols★★★☆☆⏱ 25 min
Alcohols undergo four core reaction classes tested in exams: combustion, oxidation, substitution to form halogenoalkanes, and elimination (dehydration) to form alkenes. Oxidation is the most frequently examined, with products dependent on alcohol classification.
Other key reactions: Substitution with $PCl_5$, $SOCl_2$ or $HCl/ZnCl_2$ replaces -OH with -Cl to form a halogenoalkane. Dehydration (elimination) with concentrated acid catalyst eliminates water to form an alkene, following Zaitsev's rule (more substituted alkene = major product).
4. Chemical Identification of Alcohols★★☆☆☆⏱ 10 min
Alcohols can be identified via simple chemical tests, as well as spectroscopic methods covered in other subtopics. The standard test for a hydroxyl group is reaction with sodium metal.
Common Pitfalls
Why: Tertiary alcohols have no C-H bond on the hydroxyl-bearing carbon, so oxidation cannot occur without breaking the carbon skeleton
Why: Reflux with excess oxidising agent gives full oxidation to carboxylic acid; aldehyde is only collected if distilled off immediately
Why: Different conditions give completely different products, a common 1-2 mark exam question
Why: Only oxidisable alcohols cause the color change; tertiary alcohols do not react