10. Organic chemistry - 10.1 Introductory topics

In each of the sections, 10.1 to 10.8, candidates will be expected to be able to predict the reaction products of a given compound in reactions that are chemically similar to those specified.

Structural formulae:

In candidates’ answers, an acceptable response to a request for a structural formula will be to give the minimal detail, using conventional groups, for an unambiguous structure, e.g. CH3CH2CH2OH for propan-1-ol, not C3H7OH.

Displayed formulae

A displayed formula should show both the relative placing of atoms and the number of bonds between them, e.g.

for ethanoic acid.

Skeletal formulae

A skeletal formula is a simplified representation of an organic formula. It is derived from the structural formula by removing hydrogen atoms (and their associated bonds) and carbon atoms from alkyl chains, leaving just the carbon-carbon bonds in the carbon skeleton and the associated functional groups. Skeletal or partial-skeletal representations may be used in question papers and are acceptable in candidates’ answers where they are unambiguous. The skeletal formula for butan-2-ol and a partial-skeletal formula for cholesterol are shown below.

The hexagon convention for representing the aromatic ring is preferred.

Optical Isomers

When drawing a pair of optical isomers, candidates should indicate the three-dimensional structures according to the convention used in the example below.


I - Molecular, structural and empirical formulae

II - Functional groups and the naming of organic compounds

III - Characteristic organic reactions

IV - Shapes of organic molecules; sigma and pi bonds

V - Isomerism: structural; cistrans; optical

Learning outcomes

Candidates should be able to:

(a) *interpret, and use the nomenclature, general formulae and displayed formulae of the following classes of compound:

(b) interpret, and use the following terminology associated with organic reactions:

(c) Shapes of molecules

(d) *explain the shapes of the ethane, ethene and benzene molecules in terms of ó and ð carbon-carbon bonds

(e) describe structural isomerism

(f) describe cis-trans isomerism in alkenes, and explain its origin in terms of restricted rotation due to the presence of ð bonds

(g) *explain what is meant by a chiral centre and that such a centre gives rise to optical isomerism

(h) deduce the possible isomers for an organic molecule of known molecular formula

(i) identify chiral centres and/or cis-trans isomerism in a molecule of given structural formula