Arrange the following comounds in increasing order of length of their `C-N` bond.

Options

A. `IV lt II lt IV lt III`
B. `III lt IV lt II lt I`
C. `II lt III lt I lt IV`
D. `II lt IV lt I lt III`

Answer

B

Explanation

The bond order of `C-N` bond is `2` in `III`, shortest, `I` in `II`, longest bond. There is greater extent of delocalisation of nitrogen lone pair in `IV` because it brings negative charge on oxygen than in `IV` because it brings negative charge on oxygen than in `1` where negative charge moves on carbons. Hence, `C-N` bond acquire greater partial double bond character in `IV` than in `1`. this results in greater shortening of `C-N` bond length in `IV` than in `I`, although `I` has more resonating structure.