These are unsaturated non-cyclic hydrocarbons which have sp2 - hybridization with 120° bond angle.
Alkenes are also called olefins [oil.forming] which indicate their highly reactive nature.
Alkenes have general formula Cn H2n, where n = 2,3,4 …
C2H4 (ethene), C3H6 (propene), etc.
Methods of Preparation of Alkenes:
(i) From alkynes:
(ii) From alkyl halide [dehydrohalgenation]:
(iii) From vicinal dihalides:
(iv) From alcohols by acidic dehydrogenation: