Carboxylic Acids and Their Derivatives

Functional Group Overview

  • The chapter deals with carboxylic acids and their derivatives (esters, amides, anhydrides).
  • Carboxylic acids are terminal, contain both a carbonyl C=O\mathrm{C=O} and a hydroxyl −OH\mathrm{-OH} on the same carbon.
  • Derivatives are obtained by replacing the hydroxyl group with another heteroatom-containing group (OR, NR$_2$, or OCOR).

Carboxylic Acids

  • Terminal functional group ⇒ the carbon bearing it is always C-1 in IUPAC numbering.
  • Most oxidized MCAT-relevant functional group:
    • Carboxyl carbon has three bonds to O.
    • Only CO2\mathrm{CO_2} (four C–O bonds) is more oxidized.
  • Highest priority in nomenclature; any other functional group becomes a prefix substituent.
Nomenclature Rules
  • Replace parent-alkane suffix “-e” with “-oic acid.”
  • Example: Ethan + oic acid → ethanoic acid.
Common vs. IUPAC Names (MEMORIZE for MCAT)
  • Formic acid = methanoic acid (1-C acid).
  • Acetic acid = ethanoic acid (2-C acid).
  • Propionic acid = propanoic acid (3-C acid).

Oxidation State & Nomenclature Priority (Connections)

  • Compared with aldehydes (also terminal), carboxylic acids outrank aldehydes for numbering and naming.
  • Because of oxidation level, they dictate parent name even when other functionals are present.

Carboxylic Acid Derivatives

  • Share same parent oxidation level (three C–O bonds) but differ in heteroatom attached.
  • Major classes: esters, amides, anhydrides.
Esters
  • Structural change: hydroxyl →\rightarrow alkoxy −OR\mathrm{-OR} (R = any alkyl).
  • Nomenclature:
    • 1st word = alkyl part of the substituent R (acts as an adjective).
    • 2nd word = parent acid name with “-oate” replacing “-oic acid.”
  • Example transformation: Formic acid + butanol → butyl methanoate.
  • Additional practiced names (know how to parse):
    • ethyl propanoate
    • propyl methanoate
    • methyl butanoate
    • propyl ethanoate
Amides
  • Structural change: hydroxyl →\rightarrow amino group −NR2\mathrm{-NR_2} (R = H or alkyl).
  • Nomenclature rules:
    • Parent acid suffix becomes “-amide.”
    • Any substituent on the nitrogen is given an N- prefix, capital N, no numbering.
  • Example names mentioned:
    • N-ethyl-N-methylbutanamide
    • N,N-dimethylethanamide
    • propanamide (no N-substituents)
Anhydrides
  • Formed by condensation (dehydration) of two carboxylic acid molecules → loss of one H2O\mathrm{H_2O}.
  • Can be cyclic (intramolecular dehydration of dicarboxylic acids) or acyclic.
  • Nomenclature:
    • If symmetrical (same parent acid), replace “acid” with “anhydride.”
    • If asymmetrical, list both acids alphabetically (no “acid”) then add “anhydride.”
  • Examples provided:
    • ethanoic anhydride (a.k.a. acetic anhydride)
    • ethanoic propenoic anhydride (mixed)
    • phthalic anhydride (cyclic)
    • succinic anhydride (cyclic)

Practical / Exam-Focused Takeaways

  • Memorize all common names (formic, acetic, propionic) and be ready to interconvert with IUPAC.
  • For derivatives, master the two-part naming of esters, the N-labeling of amides, and the symmetry rule for anhydrides.
  • Recall oxidation hierarchy: \text{COOH} > \text{aldehyde} > \text{ketone / alcohol / amine} for numbering.
  • Recognize that derivatives retain carboxyl-level oxidation (important for reaction mechanisms and reactivity trends).