Question

Give plausible explanation for: There are two 2 groups in semicarbazide. However, only one is involved in the formation of semicarbazones.

Answer 1

Semicarbazide: A water-soluble white solid derived from urea.

Formula:  H2NNHC(=O)NH2        

There are two groups in semicarbazide.

However, only one is involved in the formation of semicarbazones.

Reason:

• The unavailability of the lone pair of electrons
• The carbonyl carbon atom resonates with only 1 N atom and it deteriorates
• Inability to act as a nucleophile

Hence, only one is involved in the formation of semicarbazones

Answer 2

The Semicarbazide is the main compound that will go undergo the resonance which will only contain a single –NH2 group out of two.

This is attached in the carbonyl carbon atom.

Hence, the density of the electron will show that the –NH2 group which will decrease the resonance.

Hence, we can’t act Nucleophile due to the absence of another –NH2 group.

Another group will work out as the nucleophile which will attach the atom of the carbonyl carbon of ketones and aldehydes to give out semicarbazones.