Identify structural (constitutional) isomers by their bonding patterns. The atoms of the compounds are the same but they are connected in such a way as to make different functional groups. An example would be n-butane and isobutane. N-butane is a straight hydrocarbon chain with four carbons while isobutene is branched. It consists of a straight hydrocarbon chain with three carbons and a methyl group coming off the middle carbon.

Identify stereoisomers by their arrangement in space; the compounds will have the same atoms and bonding patterns but will be arranged differently in three-dimensional space. Geometric isomers are actually a type of configurational stereoisomer.

Note whether the isomers have restricted rotation around a bond, such as a double bond. These are geometric isomers. They will have cis-trans differences across their restrictive bonds—meaning opposite placement of functional groups or atoms on either side of the bond.

Identify whether the isomers have tetrahedral centers (with four different groups and/or atoms arising from a central carbon). These are a subtype of isomer called an optical stereoisomer that can then be identified as either an enantiomer or diastereomer. If the isomers are nonsuperimposable mirror images of each other they are enantiomers; if they are nonsuperimposable nonmirror images of each other they are diastereomers.