While of the following compounds will exhibit geometrical (or cis-trans) isomerism?
(i) `CH_(3)CH=CHCH_(2)CH_(3)`
(ii) `C_(6)H_(5)CH=CHCH_(3)`
(iii) `CH_(2)=C(CH_(3))_(2)`
`(CH_(3))_(2)C=CH-C_(2)H_(5)`
Strategy: Essential requirement for any alkene to exhibit geometrical isomerism is that each of the double bonded carbon atoms should be attached to two different atoms or groups of atoms:

`m!=n and p!=r`. Notice that `m` and `p` may be same or different Similarly, `n and r` may be same or different.

Explanation

Structures (i) and (ii) will exhibit geometrical isomerism. Structures (iii) and (iv) fail to do so because two identical atosm and//or groups are attached to one of the doubly bonded carbon atoms.