10.1: Structure and Nomenclature of Alcohols and Phenols

Overview

Alcohols are one of the most important functional groups in organic chemistry. The name of alcohol comes from the hydrocarbon from which it is derived. Alcohols are organic molecules containing the functional hydroxyl or –OH group directly bonded to carbon. Phenols have an OH group directly attached to a benzene ring. While alcohols are colorless, phenol is a white crystalline compound with a characteristic "hospital smell" odor.

As with other organic compounds, alcohols and phenols are named by formal and standard systems. The most adopted system is the International Union of Pure and Applied Chemistry (IUPAC).

The IUPAC names of the alcohols are derived by adding the suffix 'ol' to the name of the parent alkane. Phenols, on the other hand, are named as hydroxy derivatives of benzene. 'Phenol' is used as the parent name rather than benzene.

Like all organic compounds, alcohols and phenols have several commercial applications. For instance, ethanol is the main ingredient in alcoholic beverages like wine or beer. Phenols are widely used as antiseptics and as disinfectants.

Naming Alcohols

The table below shows the classification and nomenclature of some alcohols and phenols.

Skeletal Structures	IUPAC Name	Common Name
	1-butanol	n-butyl alcohol
	2-butanol	sec-butyl alcohol
	2-methyl-2-butanol	t-amyl alcohol
	2-bromo-4-chlorocyclopentanol	-
	2-propen-1-ol	allyl alcohol
	3-cyclohexen-1-ol	-
	1,2-ethanediol	ethylene glycol
	1,2,3-propanetriol	glycerol
	phenol	phenol
	benzene-1,3-diol	resorcinol
	2-methylphenol	o-cresol
	3-methylphenol	m-cresol
	4-methylphenol	p-cresol

Alcohols, represented by the general formula C_nH_2n+1OH, are organic compounds with a hydroxy group attached to an sp³-hybridized carbon of an aliphatic system.

They exhibit a bent geometry around the oxygen atom, where the sp³ hybrid orbital of oxygen overlaps with the sp³ hybrid orbital of carbon, forming a sigma bond. The carbon–oxygen–hydrogen bond angle approximates the tetrahedral value of 109.5°.

Alcohols are classified as primary, secondary, or tertiary depending on the number of carbon atoms attached to the carbon bearing the –OH group.

The common names for alcohols add 'alcohol' to the name of the alkyl group attached to the hydroxy group.

The IUPAC names are derived from the name of the parent chain by replacing the final '–e' of the suffix with '–ol'. The locant may be before either the parent name or the suffix.

When identifying and numbering the parent chain, the hydroxy group takes precedence, followed by pi bonds, chain length, and lower-priority substituents.

Cyclic alcohols add the prefix 'cyclo' to the parent chain's name. The carbon bearing the –OH group is numbered as one.

When naming polyols, the final '–e' of the parent chain is retained, and multiplier prefixes, like 'di' and 'tri' are added to the suffix '–ol'. The locants of the hydroxy groups are listed together.

Phenols are compounds in which a hydroxy group is attached to an sp²-hybridized carbon of an aromatic ring.

They are named after the parent compound phenol, the simplest hydroxy derivative of benzene. The carbon atom bearing the –OH group is numbered as one.

As with alcohols, polyhydroxy phenols expand the suffix with multiplier prefixes, such as 'diol' or 'triol', and group the relevant locants.

Being aromatic, substituted phenols may use the terms ortho, meta, and para to denote the position of a lower-priority substituent relative to the hydroxy group.