Cis/trans isomers, also

Cis-trans isomers (also called geometric isomers) result from restricted rotation (Section 3.4). Restricted rotation can be caused either by a double bond or by a cyclic structure. As a result of the restricted rotation about a carbon-carbon double bond, an alkene such as 2-pentene can exist as cis and trans isomers. The cis isomer has the hydrogens on the same side of the double bond, whereas the trans isomer has the hydrogens on opposite sides of the double bond. 

Cis-trans isomers, also referred to as geometrical isomers, are a type of stereoisomer. Other types are discussed in this chapter. Stereoisomers do not differ from each other in connectivity (the order of attachment of atoms to each other). Stereoisomers differ in configuration, i.e., the arrangement of their atoms in space. 

The first type of stereoisomers we will look at are cis-trans isomers (also called geometric isomers). These isomers result from restricted rotation. Restricted rotation can be caused either by a cyclic structure or by a double bond. 

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