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Pancyprian Chemistry study materials
Pancyprian Chemistry study resources

Pancyprian Chemistry: Organic Chemistry: Structure, Nomenclature and Reactions

Pancyprian Chemistry · Work through your exam, one topic at a time.

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Organic Chemistry: Structure, Nomenclature and Reactions

This domain tests systematic naming, isomerism, the characteristic reactions of each homologous series, and the mechanisms used to explain them.

Nomenclature and isomerism

Find the longest chain containing the principal functional group, number to give it the lowest locant, then name substituents alphabetically with locants. Priority order: carboxylic acid > ester > amide > aldehyde > ketone > alcohol > amine > alkene > alkyne > halogen. Isomerism includes chain, position and functional group isomerism, cis–trans (each alkene carbon needs two different groups) and optical isomerism (a chiral carbon with four different groups).

Reaction types

Alkanes undergo free-radical substitution with halogens (initiation, propagation, termination). Alkenes undergo electrophilic addition, following Markovnikov's rule, because the more stable carbocation forms; bromine water decolourises. Haloalkanes undergo nucleophilic substitution (SN1 for tertiary, SN2 for primary) and elimination with hot ethanolic KOH. Alcohols are oxidised: primary to aldehyde then acid (distil for the aldehyde, reflux for the acid), secondary to ketone, tertiary not oxidised. Carboxylic acids with alcohols give esters under acid catalysis; esters hydrolyse under acid or alkali.

Tests

Bromine water for C=C; acidified KMnO4 for C=C and for primary/secondary alcohols; Fehling's or Tollens' for aldehydes; sodium carbonate for carboxylic acids (CO2 evolved); iodoform test for CH3CO– and CH3CH(OH)–.

Worked example

Name CH3CH(CH3)CH2CH2OH. The longest chain carrying OH has four carbons, so the parent is butan-1-ol. Numbering from the OH end puts the methyl group at carbon 3. The name is 3-methylbutan-1-ol.

Traps that cost marks

  • Numbering from the wrong end and losing the lowest locant for the principal group.
  • Naming an aldehyde as a ketone or missing the '-al' ending.
  • Applying Markovnikov without explaining carbocation stability.
  • Claiming primary alcohols cannot give carboxylic acids; reflux with excess oxidant does.
  • Writing cis/trans for an alkene carbon carrying two identical groups.