Carboxylic Acids

Lesson

Part 1 — compounds with the –COOH group: names, structure, preparation and acid strength.

In this lesson you will

Classify and name mono- and dicarboxylic acids and describe the carboxyl group
Explain high boiling points using hydrogen-bonded dimers
Write equations to prepare aliphatic and aromatic acids from alcohols, aldehydes, nitriles and Grignard reagents
Arrange acids in order of strength using inductive and resonance effects

Table of familiar carboxylic acids
Acid	Where you meet it
Methanoic (formic) acid	Ant and nettle stings
Ethanoic (acetic) acid	Vinegar (about 5%)
Butanoic (butyric) acid	Smell of rancid butter
Ethanedioic (oxalic) acid	Spinach, rhubarb; rust remover
Benzoic acid	Food preservative (as sodium benzoate)

Concept

Classification and nomenclature

Monocarboxylic (CₙH₂ₙ₊₁COOH) and dicarboxylic acids; aliphatic and aromatic. IUPAC: replace -e by -oic acid (C of COOH = C-1); diacids: -dioic acid.

Table of names of carboxylic acids
Formula	Common name	IUPAC name
HCOOH	Formic acid	Methanoic acid
CH₃CH₂CH₂COOH	Butyric acid	Butanoic acid
(CH₃)₂CHCOOH	Isobutyric acid	2-Methylpropanoic acid
HOOC–COOH	Oxalic acid	Ethanedioic acid
HOOC(CH₂)₂COOH	Succinic acid	Butanedioic acid
HOOC(CH₂)₄COOH	Adipic acid	Hexanedioic acid
C₆H₄(COOH)₂ (1,2)	Phthalic acid	Benzene-1,2-dicarboxylic acid

Concept

Structure and physical properties

The carboxyl carbon is sp²; the –OH lone pair is delocalised into C=O, so the C=O is less reactive than in aldehydes. Acids form hydrogen-bonded dimers (even in the vapour), so they boil higher than alcohols of similar mass. C1–C4 acids are miscible with water; solubility falls with chain length. Lower acids have sharp smells; higher ones are waxy solids.

Table of boiling points of compounds of similar mass
Compound (M ≈ 60)	b.p. / K	Reason
Propanal	322	Dipole–dipole
Propan-1-ol	370	H-bonding (chains)
Ethanoic acid	391	H-bonded dimers

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