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FY13CE Chemistry study materials
FY13CE Chemistry study resources

FY13CE Chemistry: Organic Chemistry and Functional Groups

FY13CE Chemistry · Work through your exam, one topic at a time.

All guide sections

Organic Chemistry and Functional Groups

This domain tests nomenclature, functional group recognition, structural, geometric and optical isomerism, reaction mechanisms and types, and the test-tube reactions that distinguish aldehydes, ketones, alkenes and alcohols.

Nomenclature and isomerism

  • Choose the longest chain containing the principal functional group, number to give the lowest locants, and apply the priority order: carboxylic acid > ester > amide > aldehyde > ketone > alcohol > amine > alkene > alkane.
  • Structural isomers differ in connectivity; positional isomers differ in where a group sits; geometric isomers need a C=C with two different groups on each carbon; optical isomers need a chiral carbon bearing four different groups.

Reaction types

  • Alkanes undergo free-radical substitution with Cl2 or Br2 under UV light.
  • Alkenes undergo electrophilic addition; Markovnikov's rule places H on the carbon with more hydrogens; bromine water is decolourised.
  • Primary alcohols oxidise to aldehydes and then carboxylic acids with acidified dichromate; secondary alcohols give ketones; tertiary alcohols resist oxidation.
  • Haloalkanes undergo substitution (aqueous KOH) or elimination (hot ethanolic KOH).
  • Carbonyls: 2,4-dinitrophenylhydrazine gives an orange precipitate with any aldehyde or ketone; Tollens' reagent and Fehling's solution react only with aldehydes.
  • Carboxylic acids with alcohols form esters under acid catalysis; esters hydrolyse back.

Worked example

A compound of formula C3H6O gives an orange precipitate with 2,4-DNP but no silver mirror with Tollens' reagent. Degree of unsaturation = (2×3 + 2 − 6)/2 = 1, consistent with one C=O. Positive 2,4-DNP confirms a carbonyl; the negative Tollens' test rules out an aldehyde, so the compound is the ketone propanone.

Traps that cost marks

  • Using Tollens' and Fehling's interchangeably, or expecting them to react with ketones.
  • Thinking tertiary alcohols oxidise to ketones.
  • Applying Markovnikov's rule backwards.
  • Calling any carbon with four bonds chiral; the four groups must differ.
  • Missing the C=C requirement that each carbon carries two different substituents for geometric isomerism.