Read a molecule’s signature.
Functional groups help predict characteristic reactions: hydroxyl in alcohols, carboxyl in carboxylic acids, carbonyl in aldehydes and ketones, and ester, amino and amide groups in their respective classes. Haloalkanes contain a carbon–halogen bond.
Alkanes contain only C–C single bonds; alkenes contain C=C and alkynes C≡C. Members of a homologous series share a functional group and a general pattern, with successive members differing by CH₂.
A molecular formula gives actual atom counts; an empirical formula gives their simplest ratio; a structural formula shows connections. C₂H₆O can represent ethanol or dimethyl ether, so a molecular formula alone does not determine structure.
Spot the functional group
Condensed structural diagrams. Bonds show connectivity, not measured bond angles. Compare the molecular formula with the arrangement of atoms.
Explore: Compare functional groups and the different behaviour they give similar carbon skeletons.
Give the empirical formula of C₆H₁₂O₆ and explain the reduction.
- The atom ratio is 6:12:6.
- Dividing by 6 gives 1:2:1, hence CH₂O.
Answer: CH₂O; divide every subscript by 6.
Assumed knowledge
Carbon forms four bonds in these neutral structures; oxygen two.
Learning checkpoints & source
YOUR SYLLABUS CHECKPOINT- Recognise organic classes and functional groups.
- Distinguish molecular, empirical and structural formulas.
- Identify saturated and unsaturated compounds.