Question

The correct order of decreasing basic strengths of x, y and z is:

• A. x > y > z
• B. x > z > y
• C. y > x > z
• D. y > z > x

Answer 1

Answer: (B)

x > z > y

Answer 2

The basicity of a nitrogen compound is determined by the availability of the lone pair of electrons on the nitrogen atom.

• Compound (x) is cyclohexylamine, a secondary aliphatic amine. The nitrogen atom is $sp^3$ hybridized, and its lone pair is readily available for protonation. The cyclohexyl ring is electron-donating, enhancing the electron density on nitrogen.
• Compound (y) is a cyclic amide (lactam). The nitrogen atom is $sp^2$ hybridized and its lone pair is delocalized through resonance with the adjacent carbonyl group (C=O). This delocalization significantly reduces the availability of the lone pair for protonation, making amides very weak bases.
• Compound (z) is a cyclic imine. The nitrogen atom is $sp^2$ hybridized. The lone pair resides in an $sp^2$ orbital, which is less available than in an $sp^3$ orbital. However, unlike amides, the lone pair is not delocalized by resonance with a carbonyl group. Thus, imines are less basic than amines but more basic than amides.

Therefore, the order of decreasing basic strengths is: Amine (x) > Imine (z) > Amide (y) This translates to the order x > z > y.