The A Level year brings benzene rings, phenols, acyl chlorides, amines, amides and amino acids. The naming rules you already know still apply: find the parent, number to give the lowest locants, and list substituents in alphabetical order.
At A Level the organic toolkit grows. An arene contains a benzene ring (C6H5– is the phenyl group); a halogenoarene has a halogen joined directly to the ring; a phenol has –OH joined directly to the ring. Acyl chlorides (RCOCl), amides (RCONH2) and nitriles (RCN) are named from the parent acid or alkane, counting the functional carbon. Amines are classified by the number of carbon groups bonded to the nitrogen: one (primary, RNH2), two (secondary, R2NH) or three (tertiary, R3N). An amino acid has both –NH2 and –COOH, and 2-amino acids carry both on the same carbon. On a benzene ring, substituents get locants numbered to be as low as possible, as in 1,3-dinitrobenzene.
Pick each A Level functional group in the simulator and see it highlighted on a molecule, then watch how the suffix or prefix changes the name.
| Homologous series | Functional group | Example | Name |
|---|---|---|---|
| arene | benzene ring | C6H5CH3 | methylbenzene |
| halogenoarene | X joined to the ring | C6H5Cl | chlorobenzene |
| phenol | –OH joined to the ring | C6H5OH | phenol |
| acyl chloride | –COCl | CH3COCl | ethanoyl chloride |
| amide | –CONH2 | CH3CONH2 | ethanamide |
| amine | –NH2 | CH3CH2NH2 | ethylamine |
| amino acid | –NH2 and –COOH | CH3CH(NH2)COOH | 2-aminopropanoic acid |
| nitrile | –C≡N | CH3CN | ethanenitrile |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
What is the name of CH3COCl?
Which compound is a secondary amine?
Which compound is a phenol?
What is the functional group of an amide?
Two or more substituents on a benzene ring need numbers. Start at one substituent and go round the ring the way that gives the lowest set of numbers.
| Structure | Name | Rule used |
|---|---|---|
| two NO2 groups with one carbon between them | 1,3-dinitrobenzene | lowest locants; “di” for two identical groups |
| CH3 and NO2 on opposite carbons | 1-methyl-4-nitrobenzene | alphabetical order, methyl gets 1 |
| OH with NO2 opposite | 4-nitrophenol | the –OH carbon of phenol is always C1 |
| OH with three Br atoms | 2,4,6-tribromophenol | number from the C–OH carbon |
Amines are classified by counting the carbon groups on the nitrogen, not by the type of carbon the nitrogen is on: (CH3)3CNH2 is a primary amine even though it would be a tertiary alcohol if the NH2 were OH. Phenol has –OH directly on the ring; C6H5CH2OH is an alcohol (phenylmethanol). Chlorobenzene is a halogenoarene; C6H5CH2Cl, with Cl on a side chain, behaves like a halogenoalkane.
Unlocks once the four checks above are done. Worth more XP, written to A Level Paper 4 standard.
Which name is correct for a benzene ring carrying two nitro groups separated by one ring carbon?
How should (CH3)3CNH2 be classified?
What is the percentage by mass of nitrogen in 1,3-dinitrobenzene, C6H4(NO2)2?
Which compound contains BOTH a primary amine group and a carboxylic acid group?
This skill is now recorded on your profile. Keep the chain going.