Carboxylic Acids and Their Derivatives: One Carbon, Four Families

In the paper

Unit 3, Organic chemistry, carries 17 of the 50 chemistry marks — the heaviest unit in the subject. With eleven chapters sharing them, this one averages a little over one and a half (MEC publishes weights by unit, not by chapter). It is also the chapter that ties the others together: every derivative here is made from an acid, and the acid itself is made from an alcohol, an aldehyde, a nitrile or a Grignard reagent.

MEC scope: Nomenclature and isomerism; Preparation and chemical properties of monocarboxylic acids; Preparation, properties and relative reactivity of acid halides, anhydrides, amides and esters.

Three ways it is asked:

• Recall: the reagent that turns an acid into an acid chloride; what soda lime does; the smell of a named ester.
• Understanding: why ethanoic acid boils higher than propan-1-ol of the same molar mass; why an amide is the least reactive derivative; why a carboxylic acid will not reduce to an aldehyde with LiAlH₄.
• Application: arrange four substituted acids by pKa; decide which acid a given Grignard reagent and CO₂ will give; pick the derivative that hydrolyses fastest.