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4.7: Naming Alcohols and Phenols

Fundamental Organic ala Mech · LibreTexts

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    Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°), depending on the number of organic groups bonded to the hydroxyl-bearing carbon.

    The structures of primary, secondary, and tertiary alcohol. Primary alcohol has one R group, secondary has two R groups and tertiary has three R groups linked to the carbon atom.

    Simple alcohols are named in the IUPAC system as derivatives of the parent alkane, using the suffix -ol.

    Alcohol Nomenclature

    RULE 1: Select the longest carbon chain containing the hydroxyl group, and derive the parent name by replacing the -e ending of the corresponding alkane with -ol. The -e is deleted to prevent the occurrence of two adjacent vowels: propanol rather than propaneol, for example.

    RULE 2: Number the alkane chain beginning at the end nearer the hydroxyl group.

    RULE 3: Number the substituents according to their position on the chain, and write the name, listing the substituents in alphabetical order and identifying the position to which the –OH is bonded. Note that in naming cis-1,4-cyclohexanediol, the final -e of cyclohexane is not deleted because the next letter, d, is not a vowel; that is, cyclohexanediol rather than cyclohexandiol. Also, as with alkenes (Section 7.3), newer IUPAC naming recommendations place the locant immediately before the suffix rather than before the parent.

    The structures of three alcohols. The old names include 2-methyl-2-pentanol, cis-1,4-cyclohexanediol, and 3-phenyl-2-butanol. The new names of these structures are 2-methylpentan-2-ol, cis-cyclohexane-1,4-diol, and 3-phenylbutan-2-ol.

    Some simple and widely occurring alcohols have common names that are accepted by IUPAC. For example:

    The structures of five alcohols named benzyl alcohol (phenylmethanol), allyl alcohol (2-propen-1-ol), tert-butyl alcohol (2-methyl-2-propanol), ethylene glycol (1,2-ethanediol) and glycerol (1,2,3-propanetriol).

    Phenols are named as described previously for aromatic compounds according to the rules discussed in Section 15.1, with -phenol used as the parent name rather than -benzene.

    Two structures of cyclic alcohols. They include m-methylphenol (m-cresol), and 2,4-dinitrophenol.
    Exercise \(\PageIndex{1}\)
    Give IUPAC names for the following compounds:
    1. a=
    2. A four-carbon chain with hydroxyl and methyl on C 2, and a benzene ring on C 4 position.
    3. The structure of cyclohexanol with two methyl groups on the C 4 position.
    4. Cyclopentane ring with hydrogen on wedge and bromine on dash. On the adjacent (clockwise) carbon, hydroxyl on wedge and hydrogen on dash.
    5. A phenol with methyl two carbons and bromine three carbons from the hydroxyl carbon.
    6. Cyclopentene with a hydroxyl on a carbon adjacent to the double bond.
    Answer
    1. 5-Methyl-2,4-hexanediol
    2. 2-Methyl-4-phenyl-2-butanol
    3. 4,4-Dimethylcyclohexanol
    4. trans-2-Bromocyclopentanol
    5. 4-Bromo-3-methylphenol
    6. 2-Cyclopenten-1-ol
    Exercise \(\PageIndex{2}\)

    Draw structures corresponding to the following IUPAC names:

    1. (Z)-2-Ethyl-2-buten-1-ol
    2. 3-Cyclohexen-1-ol
    3. trans-3-Chlorocycloheptanol
    4. 1,4-Pentanediol
    5. 2,6-Dimethylphenol
    6. o-(2-Hydroxyethyl)phenol
    Answer
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