16.1.4—CH3CH(OH)- alcohol identification
- Syllabus
- 9701–2028–2029
- Objective
- 16.1.4
- Level
- AS
The iodoform test detects a CH₃CH(OH)– group through yellow CHI₃
An alcohol containing CH₃CH(OH)– is oxidised under alkaline iodine conditions to a methyl-carbonyl intermediate, which gives a yellow precipitate of triiodomethane, CHI₃.
The test also applies to compounds that can form the same CH₃CO– pattern after oxidation. Identify the structural motif before using the observation as evidence.
Ethanol gives the yellow iodoform precipitate because it oxidises to ethanal, which contains the required methyl-carbonyl group. Propan-1-ol does not give this test.
A yellow precipitate is not a general alcohol test; it points to the specific methyl-containing motif.
ConceptA-Level CAIE Chemistry AS