Mono, di, tri and polyhydric compounds

Monohydric, dihydric, trihydric and polyhydric compounds are alcohols/phenols bearing one, two, three, or more -OH groups respectively in their molecule: ethanol (CH3-CH2-OH) is monohydric, ethylene glycol (HOCH2-CH2OH) is dihydric, and glycerol (HOCH2-CH(OH)-CH2OH) is trihydric; the same one/two/three-OH classification applies equally to phenols (e.g. catechol, resorcinol and hydroquinone are dihydric phenols; phloroglucinol and pyrogallol are trihydric phenols). Within the monohydric alcohols, those whose -OH is bonded to an ORDINARY sp3-hybridised carbon (an alkyl-group carbon, not part of any C=C) are classified by how many other carbon-containing groups are attached to that same carbon: primary (1 degree, one R group plus two H's, pattern R-CH2-OH), secondary (2 degree, two R groups plus one H, pattern R2CH-OH), or tertiary (3 degree, three R groups and no H, pattern R3C-OH). A separate, structurally distinct class is the vinylic alcohol, in which the -OH group sits on an sp2-hybridised carbon that is itself part of a carbon-carbon double bond, the simplest example being vinyl alcohol, CH2=CH-OH. Independently of the primary/secondary/tertiary classification, any sp3 alcohol whose -OH-bearing carbon is ALSO directly bonded to a C=C double bond is further called allylic (it may still be primary, secondary or tertiary), and any sp3 alcohol whose -OH-bearing carbon is instead bonded to …