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
- Statement I is true but Statement II is false
- Statement I is false but Statement II is true
- Both Statement I and Statement II are false
Answer
(2) Statement I is true but Statement II is false
Solution
But-2-enal is a conjugated system and shows resonance (−R effect of C=O):
CH3-CH=CH-CH=O CH3- CH-CH=CH- O
Statement I: in but-2-enal the charges are separated over a longer distance (C-3 to O) in the polar resonance form, so = q d is larger than in butanal, where only the C=O group is polar. True.
Statement II: due to resonance the C1-C2 bond of but-2-enal has partial double bond character and joins two sp2 carbons, while in butanal it is a pure single bond between sp2 C-1 and sp3 C-2. So the C1-C2 bond in but-2-enal is shorter. False.
Answer: (2)