Question

How many geometrical isomers are possible in the following two alkenes?

(a) CH₃ - CH = CH - CH = Ch - CH₃

(b) CH₃ - CH = CH - CH = Ch -Cl

(a) 4 and 4

(b) 4 and 3

(c) 3 and 3

(d) 3 and 4

Answer 1

Correct option (d) 3 and 4

Explanation:

When the ends of alkene containing n double bonds are different, the number of geometrical isomers is 2ⁿ. Thus for

CH₃ - CH = CH - CH = CH - Cl.

Number of geometrical isomers = 2² = 4

When the ends of alkene containing n double bonds are same, then the number of geometrical isomers = 2^n-1 + 2^p-1.

where, P = n/2 for even n and n+1/2 for odd n, thus

For CH₃ - CH = CH - CH = CH - CH₃

Number of geometrical isomers