Question

Why does only one nh2 group react in semicarbazide?

Answer 1

Because it is strong enough nucleophile to react with the carbonyl group of an aldehyde or ketone, while the other one is not (its lone pair of elections is drawn away by the adjacent CO through resonance). ... So there is only one Nh2 group present for reaction.

Answer 2

Semicarbazide: The chemical compound derived from urea with the formula OC. It is a water-soluble white solid.

Its chemical formula is ‎H2NNHC(=O)NH2        

There are two groups in semicarbazide.

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

Reason:

• One N atom is involved in resonance with the carbonyl carbon atom
• Lone pair is not available for bonding.
• The electron density on - NH2 group involved in the resonance decreases.  
• It cannot act as a nucleophile.  
• It can act as a nucleophile and can attack carbonyl-carbon atoms of aldehydes and ketones to produce semicarbazones.

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

Read more on Brainly.in - https://brainly.in/question/6263813