How many constututional isomers are possible for the alkene `C_4H_8`?

Options

A. Two
B. Three
C. Four
D. Five

Answer

B

Explanation

Both chain and position isomerism are possible for alkenes. First make different skeletons of four carbons and then introduce and double bond at different location: `underset("But-1-ene")(H_(2)C=CHCH_(2)CH_(3))" "underset("but-2-ene")(H_(3)C CH=CHCH_(3))`
`underset("Methylpropene (III)")(CH_(3)-underset(CH_(3))underset(|)(C)=CH_(2))`
(I) and (II) exhibit position isomerism (I) and (III) exhibit chaibn isomerism, and (II) and (III) exhibit both chains and position isomerism.