Question

Which of the following(s) will not be able to show optical isomerism?

• A. $1,2-$Propadiene
• B. $2,3-$ Pentadiene
• C. $sec-$Butyl alcohol
• D. $2,3,4-$Hexatriene

Answer 1

Answer: (A), (D)

$2,3,4-$Hexatriene

Even cumulenes show optical isomers if the terminal attached to each $s{p}^2$ carbons are different.
For allene system, to show optical isomerism both $R$ and $R_1$ should be different.

(a) $1,2-$Propadiene

$R=R_1$
It does not exhibit optical isomerism.

(b) $2,3-$ Pentadiene

$R\ne R_1$
It exhibit optical isomerism.

(c) $sec-$Butyl alcohol
It has a chiral carbon, so it exhibit optical isomerism.

(d) $2,3,4-$Hexatriene
It is a odd cumulene. Thus, its terminals are in same plane so it does not exhibit optical isomerism.