AS organic chemistry conventions and functional group reference
- Syllabus
- 9701–2028–2029
- Topic
- —
- Level
- AS
Learning objectives
—Reference—AS organic notation conventions• Use the syllabus conventions X for a halogen atom and R/R' for alkyl groups or hydrogen as appropriate.—Reference—AS organic functional groups• Recognise and use the AS organic functional groups and representations from the syllabus table.- (a) alkene: C=C bond- (b) halogenoalkane: halogen X; primary, secondary and tertiary halogenoalkanes- (c) alcohol: hydroxyl -OH; primary, secondary and tertiary alcohols- (d) aldehyde: carbonyl -CHO- (e) ketone: carbonyl >C=O- (f) carboxylic acid: carboxyl -COOH- (g) ester: ester -COO-- (h) primary amine: -NH2- (i) nitrile: -CN
Use X, R and R′ consistently in organic chemistry notation
In the syllabus, X represents a halogen atom, while R and R′ represent an alkyl group or hydrogen where appropriate. These symbols show the reaction pattern without committing to one named molecule.
Read the notation together with the functional group: R–X is a halogenoalkane, R–OH an alcohol and R–COOH a carboxylic acid. R and R′ need not be identical, and X is not a variable element chosen after the equation.
The substitution pattern R–Br + OH⁻ → R–OH + Br⁻ describes many bromoalkanes. A specific example such as CH₃CH₂Br is one member of the general family.
Do not treat R as “any atom” or replace X by a whole molecule. The symbols have fixed structural meanings.
Recognise all nine AS organic functional groups from connectivity
| Class | Functional group / general fragment | Recognition boundary |
|---|---|---|
| alkene | C=C | carbon–carbon double bond |
| halogenoalkane | R–X | X is F, Cl, Br or I; classify 1°, 2° or 3° from how many carbon atoms are bonded to the carbon bearing X |
| alcohol | R–OH | classify 1°, 2° or 3° from the carbon bearing OH |
| aldehyde | R–CHO | terminal carbonyl carbon is bonded to H |
| ketone | R–CO–R′ | carbonyl carbon is bonded to two carbon groups |
| carboxylic acid | R–COOH | carbonyl and OH belong to one carboxyl group |
| ester | R–COO–R′ | carbonyl carbon is bonded to an O that continues to another carbon group |
| primary amine | R–NH₂ | nitrogen is bonded to one carbon group and two H atoms |
| nitrile | R–C≡N | carbon chain is bonded through the nitrile carbon, not through N |
Locate the distinctive bond or atom pattern first, then inspect its neighbours. Connectivity distinguishes groups that contain the same atoms: –CHO, >C=O, –COOH and –COO– all contain C and O but represent different functional groups.
Primary, secondary and tertiary in this AS table apply to halogenoalkanes and alcohols by the substitution of the carbon carrying X or OH. The listed amine reference is specifically a primary amine, R–NH₂.