Chemistry

Carboxylic Acids

2,821 words, 11 sections

The carboxyl group, $-\text{COOH}$ , sits where the chemistry of the carbonyl and the hydroxyl meet, and the paper treats it as one large chapter rather than a set of unrelated reactions. It has been asked 175 distinct times across 78 official papers between 2000 and 2026, on six boards, and it carries a share of the 45 Chemistry marks in the paper. A student who has mastered it can name any acid, derivative and ester, rank a series of acids by strength without calculating anything, and predict the product when an acid meets a base, a carbonate, a metal, an alcohol, ammonia, thionyl chloride or lithium aluminium hydride.

The carboxyl carbon is $sp^2$ hybridised, with three orbitals roughly $120^\circ$ apart and a $p_z$ orbital that overlaps oxygen to make the $\pi$ bond. The carbonyl oxygen withdraws density, the $\text{O}-\text{H}$ bond weakens, and the hydrogen becomes acidic. A monocarboxylic acid has the general formula $\text{C}n\text{H}{2n}\text{O}_2$. IUPAC replaces the parent alkane's terminal $-e $with$ -oic$ acid, so the family is the alkanoic acids, and the trivial names must be carried alongside the systematic ones: methanoic (formic), ethanoic (acetic), propanoic (propionic), butanoic (butyric), pentanoic (valeric), hexanoic (caproic). Dicarboxylic acids add $-dioic$ acid, so $\text{HOOC}-\text{COOH}$ is ethanedioic (oxalic) acid and $\text{CH}_2(\text{COOH})_2 $is 1,3-propanedioic (malonic) acid. The derivatives follow one rule: swap the acid ending for$ -oyl$ chloride, an alkyl alkanoate, or $-amide$.

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Introduction

1. Structure and nomenclatureThe carboxyl carbon is hybridised, with three orbitals roughly apart and a orbital that overlaps oxygen to make the bond. The carbonyl oxygen withdraws density,