Consider the following statements
(i) Out of two −NH2 groups in semicarbazide only one is involved in formation of semicarbazones.
(ii) Cyclohexane froms cyanohydrin in good yield but 2,2,6−trimethylcyclohexanone does not.
(iii) The α−hydrogens in aldehydes and ketones are acidic.
Consider the following statements
(i) Out of two −NH2 groups in semicarbazide only one is involved in formation of semicarbazones.
(ii) Cyclohexane froms cyanohydrin in good yield but 2,2,6−trimethylcyclohexanone does not.
(iii) The α−hydrogens in aldehydes and ketones are acidic.
The correct option is C i and iii
(i) Out of two -NH2groups in semicarbazide, one is a part of amide functional group. In this, the lone pair on nitrogen atom is involved in the resonance with carbonyl group. Hence, this -NH2group cannot act as a nucleophile. Hence, it is not involved in the formation of semicarbazones.
(ii) In cyclohexanone, the carbonyl carbon is not hindered. Hence, the nucleophile CN-ion can easily attack the carbonyl carbon. However in 2,2,6-trimethyl cyclohexanone, the carbonyl carbon is sterically hindered due to presence of methyl groups. Hence, the nucleophile CN- ion cannot easily attack the carbonyl carbon.
(iii) This is because of simply the difference between the electronegativities of carbon and double bonded oxygen and as you know oxygen the second most electronegative element because of which partial positive and partial negative charges appears and carbon and oxygen respectively because of which dissociation of Alpha hydrogen becomes easier (as we know the acidic character is how easily a particular compound loses H ion). Thus, it show acidic character
(i) Out of two -NH2groups in semicarbazide, one is a part of amide functional group. In this, the lone pair on nitrogen atom is involved in the resonance with carbonyl group. Hence, this -NH2group cannot act as a nucleophile. Hence, it is not involved in the formation of semicarbazones.
(ii) In cyclohexanone, the carbonyl carbon is not hindered. Hence, the nucleophile CN-ion can easily attack the carbonyl carbon. However in 2,2,6-trimethyl cyclohexanone, the carbonyl carbon is sterically hindered due to presence of methyl groups. Hence, the nucleophile CN- ion cannot easily attack the carbonyl carbon.
(iii) This is because of simply the difference between the electronegativities of carbon and double bonded oxygen and as you know oxygen the second most electronegative element because of which partial positive and partial negative charges appears and carbon and oxygen respectively because of which dissociation of Alpha hydrogen becomes easier (as we know the acidic character is how easily a particular compound loses H ion). Thus, it show acidic character
