Topic overview

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For geometric isomerism, each carbon of an alkene’s C=C bond must have two different substituents. In simple cases, cis means groups are on the same side and trans means they are on opposite sides; more broadly, E/Z notation uses Cahn–Ingold–Prelog priorities. Trans (E) alkenes are generally more stable, while cis (Z) alkenes typically have a net dipole and differ in boiling and melting points. Ring size can restrict cycloalkenes to cis geometry, and heat, UV light, or acid or metal catalysis can promote isomerization. Alkynes are linear, so internal alkynes do not have cis–trans isomers. The topic also connects alkene geometry with alkyne hydrogenation, addition reactions, and spectroscopic identification.