H1 Preparation of alkenes and alkynes ■Alkynes 1.The electrophilic addition of bromine to form a vicinal dibromide then dehydrohalogenation with strong base 2.Alkylation of terminal alkynes NaNH2 heat R一C=C一R 2HBr Fig 2.Synthesis of an allyne from an alkene. College H1 Preparation of alkenes of Science and alkynes „Alkynes 1. The electrophilic addition of bromine to form a vicinal dibromide then dehydrohalogenation with strong base 2. Alkylation of terminal alkynes