Alcohols and Phenols

Alcohols

• General formula: $R-OH$, where R is any alkyl group.

• Functional group: $-OH$ (hydroxyl).

• Alcohols are a composite of an alkane and water: $(R-H) + (H_2O) \rightarrow R-OH$

• Also known as alkanol group.

Classification (Functional Group)

• Monohydric: Contains one $-OH$ group.

• Dihydric: Contains two $-OH$ groups.

• Trihydric or Triol: Contains three $-OH$ groups.

Classification (Attachment of OH)

• Primary Alcohols: The $-OH$ group is attached to a primary/terminal carbon.

• Secondary Alcohols: The $-OH$ group is attached to a secondary carbon atom (carbon attached to 2 other carbon atoms).

• Tertiary Alcohols: The $-OH$ group is attached to a tertiary carbon atom (carbon attached to 3 other carbon atoms).

Naming Alcohols

Common Names

• Alkyl alcohol

• Methyl alcohol

• Ethyl alcohol

• Propyl alcohol

• Butyl alcohol

• Pentyl alcohol

IUPAC Rules for Naming Alcohols

• 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 ending -e is deleted to prevent the occurrence of two adjacent vowels (e.g., propanol instead of propaneol).

• Number the alkane chain beginning at the end nearer the hydroxyl group.

• 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.

  • In naming cis-1,4-cyclohexanediol, the final -e of cyclohexane is not deleted because the next letter, d, is not a vowel (i.e., cyclohexanediol rather than cyclohexandiol).

  • Newer IUPAC naming recommendations place the locant immediately before the suffix rather than before the parent.

  • Examples:

    • 2-Methyl-2-pentanol (New: 2-Methylpentan-2-ol)

    • cis-1,4-Cyclohexanediol (New: cis-Cyclohexane-1,4-diol)

• Examples:

  • Allyl alcohol (2-propen-1-ol) $H<em>2C=CHCH</em>2OH$

  • tert-Butyl alcohol (2-methyl-2-propanol) $(CH<em>3)</em>3COH$

  • Ethylene glycol (1,2-ethanediol) $HOCH<em>2CH</em>2OH$

  • Glycerol (1,2,3-propanetriol) $HOCH<em>2CH(OH)CH</em>2OH$

IUPAC and Common Names of Monohydroxy Alcohols (Up to Four Carbons)

Additional Rules

• The parent chain must contain the carbon bonded to the $-OH$ group, and the carbon chain numbering must give the $-OH$ group the lowest possible number.

  • Example of correct vs incorrect parent chain selection.

  • Example of correct vs incorrect numbering of the carbon chain.

Examples

• Examples of alcohol structures and their corresponding names based on IUPAC nomenclature.

  • 2-methyl-3,4-hexanediol

  • 1-fluoro-3-methylpenta-1-ol

  • 3-ethyl-2,5-dimethylphenol

  • 2,3-dichlorocyclohexan-1-ol

  • 4-bromo-2-isopropyl-2,5-decanediol

Phenols

• Class of chemical compounds consisting of a hydroxyl group ($-OH$$) bonded directly to an aromatic hydrocarbon group.

• Phenols with a single hydroxyl group are monohydroxyl phenols.

• Phenols with more than one hydroxyl group in the molecule are polyhydroxy phenols.

• Found in coal tar and petroleum.

• Used to be called CARBOLIC ACID.

Naming Phenols

• Phenol is the IUPAC name for benzene with a hydroxyl group.

  • The IUPAC rules for naming phenols are simply extensions of the rules used to name benzene derivatives with hydrocarbon or halogen substituents.

  • Methyl and hydroxy derivatives of phenol have IUPAC-accepted common names. Methylphenols are called cresols. The name cresol applies to all three isomeric methylphenols.

  • For hydroxyphenols, each of the three isomers has a different common name.

    • Catechol

    • Resorcinol

    • Hydroquinone

Examples

• Examples of phenol structures and their corresponding names based on IUPAC nomenclature.

  • 3-bromophenol

  • hydroquinone

  • catechol

  • m-ethylphenol

  • o-cresol

  • 2,6-dichlorophenol