Question

Organic compounds containing carbonyl group as the functional group are aldehydes, ketones and carboxylic acids. The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen as compared to carbon. Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. They react with HCN, Sodium bisulphite, Grignard reagent and a number of ammonia derivatives like Hydroxylamine, Hydrazine, Semicarbazide, etc. Aldehydes and ketones undergo various reactions due to the acidic nature of \(\alpha\)-hydrogen. Aldehydes and ketones having at least one \(\alpha\)-hydrogen atom undergo a reaction in the presence of dilute alkali as a catalyst to form \(\beta\)-hydroxy aldehydes or \(\beta\)-hydroxy ketones. On the other hand, aldehydes which do not possess an \(\alpha\)-hydrogen undergo self-oxidation and reduction in the presence of concentrated alkali.

(ii) Draw the structure of the semicarbazone of cyclohexanone.

Hint:

Semicarbazide condenses with the C=O group and loses water. The ring carbon becomes C=N-NH-CO-NH2.

Answer 1

Step 1: Know the reagent:
Semicarbazide is \(\mathrm{H_2N-NH-CO-NH_2}\). Its terminal \(\mathrm{NH_2}\) attached to the \(\mathrm{NH}\) group acts as the nucleophile.
It condenses with a carbonyl group and removes water. The product has a \(\mathrm{C=N}\) bond.

Step 2: Write the reaction:
Cyclohexanone has the ring carbon C=O. The oxygen is replaced by \(\mathrm{=N-NH-CO-NH_2}\). \[ \mathrm{C_6H_{10}=O + H_2N-NH-CO-NH_2 \rightarrow C_6H_{10}=N-NH-CO-NH_2 + H_2O} \]

Step 3: Describe the structure:
A six-membered saturated carbon ring. One ring carbon is double bonded to nitrogen.
That nitrogen is bonded to NH, and the NH is bonded to a carbonyl carbon, which carries an \(\mathrm{NH_2}\) group.

Final Answer:
The product is cyclohexanone semicarbazone, a cyclohexane ring with \(\mathrm{=N-NH-C(=O)-NH_2}\) on one carbon. \[ \boxed{\mathrm{C_6H_{10}=N-NH-CO-NH_2}} \]