Terminal alkene

A terminal alkene has a carbon-carbon double bond at the end of its carbon framework, commonly written $\mathrm{RCH}=\mathrm{C}{\mathrm{H}}_2$. The terminal carbon is a methylene group.

It differs from an internal alkene whose double-bond carbons both continue into carbon substituents. This distinction affects substitution, possible geometrical isomerism, and the regioselectivity of reactions across the double bond.