A Level organic chemistry A2 conventions and functional group reference
- Syllabus
- 9701–2028–2029
- Topic
- —
- Level
- A2
Learning objectives
—Reference—A Level organic functional groups• Recognise and use the A Level organic functional groups and representations from the syllabus table.- (a) arene: benzene ring/arene system- (b) halogenoarene: halogen attached to an arene ring- (c) phenol: -OH attached to an arene ring- (d) acyl chloride: -COCl- (e) secondary and tertiary amines: amine functional group- (f) amides: primary, secondary and tertiary amide functional group- (g) amino acids: amine and carboxyl groups in the same molecule—Reference—Benzene ring representation convention• Understand: where a benzene ring is part of the molecule, a displayed formula of the ring would not be expected to be drawn.
Recognise the A Level organic functional groups from connectivity
Recognise a functional group from which atoms are directly bonded, not by spotting one atom or relying on a name. In the formulae below, R and R′ are carbon-containing groups, Ar is an arene ring, and X is a halogen.
| Family | Recognition pattern | Decisive connectivity / example |
|---|---|---|
| arene | Ar | contains a benzene ring; e.g. methylbenzene |
| halogenoarene | Ar–X | X is directly bonded to a ring carbon; e.g. chlorobenzene |
| phenol | Ar–OH | OH is directly bonded to a ring carbon; e.g. phenol |
| acyl chloride | R–C(=O)–Cl | Cl is bonded to the carbonyl carbon; e.g. CH₃COCl |
| secondary / tertiary amine | R₂NH / R₃N | N is bonded to two / three carbon groups |
| primary / secondary / tertiary amide | RCONH₂ / RCONHR′ / RCONR′R″ | N is directly bonded to a carbonyl carbon and has zero, one or two N-substituent carbon groups |
| amino acid | H₂N–CHR–CO₂H | amine and carboxyl groups occur in the same molecule; R = H gives glycine |
| Do not confuse… | Discriminating bond |
|---|---|
| halogenoarene vs halogenoalkane | Ar–X vs an sp³ carbon–X bond outside the ring |
| phenol vs aromatic alcohol | Ar–OH vs Ar–CH₂OH |
| acyl chloride vs chloro-ketone | C(=O)–Cl vs Cl elsewhere on the carbon skeleton |
| amide vs amine | amide N is directly bonded to C=O; amine N is not |
The official reference table requires recognition and use of these structures. Systematic naming of secondary and tertiary amines is not required here; later chapters teach their characteristic reactions and comparisons.
Keep a benzene ring abbreviated inside a larger displayed structure
When a benzene ring is part of a molecule, Cambridge does not expect its six carbon atoms and attached ring hydrogens to be expanded as a fully displayed formula. Keep the ring as the conventional benzene hexagon and display the substituent connectivity clearly.
| Molecule | What the representation must show |
|---|---|
| chlorobenzene | a benzene ring with Cl bonded directly to one ring vertex |
| phenol | a benzene ring with OH bonded directly to one ring vertex |
| methylbenzene | a benzene ring with CH₃ bonded to one ring vertex |
| disubstituted arene | two bonds from the correct ring vertices so their relative positions are unambiguous |
If the rest of a molecule is requested as a displayed formula, draw those non-ring atoms and bonds explicitly while leaving the benzene ring in its accepted ring representation. The bond from the ring to each substituent is still part of the required connectivity.
The ring symbol already supplies the six-carbon aromatic framework; it is not an extra atom. Do not omit a substituent bond, attach X or OH through an unintended CH₂ group, or redraw every ring C–H bond when the ring is only part of the molecule.