Q. Which of the following will react with cyclo pentanone to form an enamine?

Solution:

It is an example of Stork Enamine reaction amine, react with carbonyl compounds with at least one -H-atom and form enamine. (c) and (d) both are amine but in (c), lone pair 's on -atom are delocalised by resonance (LP 's are in conjugation with (C=O) group). Hence in (3), basic character decreases as compound to (4).