Classifying and naming

Three families in this chapter all contain an oxygen atom with single bonds:

• Alcohols: an –OH group on an sp³ carbon, a carbon with only single bonds. Example: ethanol, CH₃CH₂OH.
• Phenols: an –OH group directly on a benzene ring. Example: phenol, C₆H₅OH.
• Ethers: an oxygen between two carbon groups, R–O–R′. Example: methoxymethane, CH₃OCH₃.

Alcohols are sorted by the carbon that carries the OH: primary (1°) if that carbon is joined to one other carbon, secondary (2°) if to two, tertiary (3°) if to three. Two special cases: allylic alcohols, with the OH carbon next to a C=C double bond, and benzylic alcohols, with the OH carbon next to a benzene ring.

Alcohols and phenols can have one, two or three OH groups: monohydric, dihydric, trihydric. Ethers are symmetrical if both groups are the same (CH₃OCH₃) and unsymmetrical if they differ (CH₃OC₂H₅).

Naming alcohols (IUPAC): find the longest chain that includes the OH carbon, number it so the OH carbon gets the lowest number, and change the ending from -e to -ol: propan-2-ol, 2-methylbutan-2-ol.

Phenols are named as substituted phenols: 2-methylphenol, 4-nitrophenol. Ortho (o-), meta (m-) and para (p-) can also be used for positions 2, 3 and 4.

Ethers are named as alkoxyalkanes: the bigger group is the parent, and the smaller one with the oxygen becomes the alkoxy prefix. CH₃OCH₂CH₃ is methoxyethane; C₆H₅OCH₃ is methoxybenzene (also called anisole).