Question

Which of the following will have a meso-isomer also?

• A. 2-chlorobutane
• B. 2, 3-dichlorobutane
• C. 2, 3-dichloropentane
• D. 2-hydroxypropanoic acid

Answer 1

Answer: (B)

[a] $=C{H}_3-\underset{Cl}{\underset{|}{\stackrel{\ast }{C}}}H-C{H}_{2}C{H}_3$
One asymmetric carbon atom, forms d- and $l-$ optical isomers.
Meso due to internal compensation
[b] Two asymmetric carbon atoms, forms $d-,l-$ and meso forms.
[c] $C{H}_3-\underset{Cl}{\underset{|}{\stackrel{\ast }{\mathrm{CH}}}}-\underset{Cl}{\underset{|}{\stackrel{\ast }{\mathrm{CH}}}}-C{H}_{2}C{H}_3$
Two asymmetric carbon atoms but does not have symmetry. Hence, meso form is not formed.
[d] $C{H}_3-\underset{OH}{\underset{|}{\stackrel{\ast }{C}}}H-COOH$
One asymmetric carbon atom, meso form is not formed.