Arrange the following compounds in the correct decreasing order of their nucleophilicity: I. II. III.

Step-by-step solution

Nucleophilicity depends on the availability of the lone pair of electrons on the nitrogen atom for donation. In piperidine (III), the nitrogen atom is sp^3 hybridized and its lone pair is localized. The lesser s-character of the sp^3 orbital means the lone pair is held less tightly by the nucleus, making it highly available for donation. Thus, it is the strongest nucleophile. In pyridine (I), the nitrogen atom is sp^2 hybridized. The lone pair is localized in an sp^2 orbital and is not part of the aromatic system.