Introduction

Alcohols are organic compounds whose molecules carry a hydroxyl group, -OH, attached to a saturated (sp3-hybridised) carbon atom. A hydroxyl group can also be present on an aromatic ring system, and this gives rise to two structurally distinct families: phenols, in which the -OH group is bonded DIRECTLY to a carbon of the benzene ring itself, and aromatic alcohols, in which the -OH group instead sits on a saturated side-chain carbon that is attached to the ring (e.g. the -CH2-OH of benzyl alcohol) rather than on the ring carbon. This one structural difference -- ring-bonded versus side-chain-bonded -OH -- is what separates the strongly acidic behaviour of phenols (covered in section 11.4.4) from the neutral behaviour of ordinary alcohols. Ethers form a related but distinct family: they are organic oxides in which an oxygen atom bridges two carbon-containing groups, which may be two alkyl groups (R-O-R'), one alkyl and one aryl group (R-O-Ar), or two aryl groups (Ar-O-Ar'). Ethers are conceptually related to alcohols as their formal anhydrides -- two molecules of alcohol losing one molecule of water between them gives an ether. A special structural subtype worth noting up front is the epoxide, a cyclic ether in which the ether oxygen is part of a strained three-membered ring, the simplest example being ethylene oxide (also named 1,2-epoxyethane); epoxides turn out to be useful synthetic intermediates and are referenced again in the preparation-of-alcohols section (11.4.1) as a route to primary alcohols via Grignard-reagent addition.