Có 4 đồng phân
CH2=CH-CH2-CH2-CH3 (Pent-2-en)
CH3-CH=CH-CH2-CH3 (Pent-2-en)
CH2 = CH - CH -CH3 (3 metyl but-1-en)
______________'
___________CH3
Và CH3 -CH = C - CH3 (3 metyl but-2-en)
_______________'
________________CH3
. CH2=CH-CH2-CH2-CH3 : pent-1-en
. CH3-CH=CH-CH2-CH3 : pent-2-en
. CH2=C(CH3)-CH2-CH3 : 2-metyl but-1-en
. CH3-C(CH3)=CH-CH3 : 3-metyl but- 2-en
. CH3-C(CH3)-CH=CH3 : 3-metyl but- 1-en
. Đồng phân hình học của pent-2-en