Given below are two statements: In the light of the above statements, choose the correct answer from the options given below:
- Both Statement I and Statement II are true
- Both Statement I and Statement II are false
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
Answer
(4) Statement I is false but Statement II is true
Solution
Statement I: In semicarbazide, the -NH2 attached to C=O is an amide nitrogen – its lone pair is delocalised into C=O, so it is not nucleophilic. The free -NH2 on the other N attacks the carbonyl carbon:
CH3-CH=O + H2N- H |N- O \|C-NH2 H+
CH3-CH=N- H |N- O \|C-NH2 + H2O (acetaldehyde semicarbazone)
⇒ the product given in Statement I (C=N bonded directly to C=O) is wrong ∴ Statement I is false.
Statement II: Ph-CH(OH)(OCH3) is a hemiacetal; in dilute acid it is hydrolysed back to the aldehyde and alcohol:
Ph-CH(OH)(OCH3) H3O+ Ph-CH=O + CH3OH
∴ Statement II is true.
Answer: (4)