Carboxylic Acid Naming Rules

Overview

This lecture covers the rules and patterns for naming carboxylic acids and their main derivatives when they are the highest priority functional group in a molecule.

Functional Group Priority and Scope

• Carboxylic acids and their derivatives are named as the highest priority group in a structure.
• Derivatives include acid halides (chlorides, bromides), anhydrides, esters, amides, and nitriles.
• Lower priority functional groups become prefixes, but this is rarely encountered in practice.

Naming Carboxylic Acids

• Carboxylic acids are always located at carbon 1 of a chain, which is never numbered in the name.
• The suffix “-oic acid” is used after the alkane root, dropping the “e” (e.g., propanoic acid).
• Common names to know: ethanoic acid = acetic acid, propanoic acid = propionic acid, butanoic acid = butyric acid.
• For rings, use the name “cycloalkane carboxylic acid” (e.g., cyclopentane carboxylic acid).

Naming Acid Anhydrides

• Anhydrides are named from the component carboxylic acids, listed alphabetically followed by “anhydride”.
• Asymmetric: both acid names appear (e.g., butanoic propanoic anhydride).
• Symmetric: use one acid name only (e.g., propanoic anhydride).

Naming Esters

• Two-word name: 1) Alkyl group attached to oxygen, 2) Parent acid as "alkanoate" (e.g., ethyl butanoate).
• Substituents on the acid chain are included as prefixes with locants (e.g., ethyl 3-methylbutanoate).

Naming Acid Halides

• Name the longest carbon chain and use the suffix “-oyl chloride” or “-oyl bromide” (e.g., propanoyl chloride).
• Drop the terminal “e” from the alkane root before adding suffix.

Naming Amides

• Use the suffix “-amide” (e.g., propanamide), drop “e” from alkane root.
• Substituents on the main chain are numbered as usual (e.g., 2-methylpropanamide).
• Substituents on the nitrogen are indicated by “N-” (e.g., N-methylpropanamide).

Naming Nitriles

• The carbon of the nitrile group counts as carbon 1 in the main chain.
• The suffix “-nitrile” is added to the alkane root (e.g., propanenitrile).
• Do not drop the “e” from the alkane root.

Key Terms & Definitions

• Carboxylic acid — Compound with a -COOH group.
• Acid anhydride — Compound formed by removal of water from two acids.
• Ester — Compound with the group -COOR, where R is an alkyl.
• Acid halide (acyl halide) — Compound with a -COX group, where X is a halogen.
• Amide — Compound with a -CONH₂, -CONHR, or -CONR₂ group.
• Nitrile — Compound with a -C≡N group.

Action Items / Next Steps

• Review common and IUPAC names for 2-4 carbon carboxylic acids.
• Practice naming problems for each derivative type.
• Refer to the provided study guide and practice problems for further learning.