ABSTRACT
Geometric isomers Compounds that only differ in three-dimensional structure by virtue of the relative positions of sets of substituents on a carbon-carbon double bond, or carbon-carbon bond
constrained in a ring, are referred to as geometric isomers. An example of geometric isomerism is offered by but-2-ene (Section E1). The isomer with the methyl groups on the same side of the double bond is labelled cis, that with the methyls on opposite faces is labelled trans (Figure 1). Note that although other structures can be drawn for the same molecular formula (e.g. 2-methylpropene), these are not geometric isomers of but-2-ene.
