Question

The CORRECT order of indicated bond length is :-

• A. d$_{C-Cl}$; CF$_{3}$-Cl > CH$_{3}$-Cl
• B. d$_{C-H}$; CF$_{3}$-H < Cl$_{3}$C-H
• C. d$_{N-N}$; H$_{2}$N-NH$_{2}$ < F$_{2}$N-NF$_{2}$
• D. d$_{O-O}$; O$_{2}$F$_{2}$> H$_{2}$O$_{2}$

Answer 1

Answer: (C)

C

Answer 2

(A) C-Cl bond in CF$_{3}$-Cl is shorter than in CH$_{3}$-Cl due to increased s-character in the C-Cl bond orbital in CF$_{3}$-Cl (Bent's rule).

(B) C-H bond in CF$_{3}$-H is longer than in Cl$_{3}$C-H. The strong electron-withdrawing effect of F makes carbon more positive in CF$_{3}$-H, weakening the C-H bond compared to Cl$_{3}$C-H.

(C) N-N bond in F$_{2}$N-NF$_{2}$ is longer than in H$_{2}$N-NH$_{2}$. The strong electron-withdrawing effect of F weakens the N-N sigma bond in F$_{2}$N-NF$_{2}$.

(D) O-O bond in O$_{2}$F$_{2}$ is much shorter than in H$_{2}$O$_{2}$ (~122 pm vs ~147 pm).

The correct order is d$_{N-N}$; H$_{2}$N-NH$_{2}$ < F$_{2}$N-NF$_{2}$.