Question

Of the following, the oxime of which compound shows geometric isomerism?
A. Acetone
B. Diethyl ketone
C. Formaldehyde
D. benzaldehyde

Answer 1

Hint: Due to the minimal rotation of C = N bond, syn and anti-configuration, the oxymes demonstrate geometric isomerism. To find the isomerism one should know reaction of above compounds in hydroxylamine

Complete step by step answer:
Geometrical isomerism occurs where atoms or groups are arranged uniquely in space due to the limited rotation of bonds or bonds in a molecule. Due to the minimal rotation of the C = N bond, the oxymes exhibit geometrical isomerism.
To differentiate them, the descriptors, syn, and anti, are used.
The syn form is where both the hydrogen and the hydroxyl ( -OH) group are on the same side of the C = N in the case of aldoximes whereas in the anti-form, they are on the opposite side. Syn and anti-descriptors, however, suggest the spatial association between the first group referred to in the name and the hydroxyl group of ketoximes. The accompanying butanone ketoxime, for example, may be referred to as either syn methyl ethyl ketoxime or anti-ethyl methyl ketoxime.
1. For benzaldehyde, $C_{6} H_{5} $
$CHO+NH_{2} OH\to C_{6} H_{5} CN(H)(OH)(anti)+C_{6} H_{5} CN(H)(OH)(syn)$
gives syn and anti-benzaldehyde oximes.
In other cases, only one product is formed.
2. For acetone,
$(CH_{3} )_{2} CO+NH_{2} OH\to H_{2} CNOH$
3. For formaldehyde,
$HCHO+NH_{2} OH\to H_{2} CNOH $
4. For diethyl ketone,
$CH_{3} CH_{2} COCH_{2} CH_{3} +NH_{2} OH\to CH_{3} CH_{2} CN(OH)CH_{3} $

So the correct option is D. benzaldehyde​

Note:
One should know the concept of geometrical isomerism, why it takes place when there is a restricted bond between carbon and nitrogen and the two types that are syn configuration and anti-configuration.