question_answer

The bond dissociation energy of \[B-F\]in \[B{{F}_{3}}\]is \[646\text{ }kJ\text{ }mo{{l}^{-1}}\]whereas that of \[C-F\]in \[C{{F}_{4}}\]is\[515\text{ }kJ\text{ }mo{{l}^{-1}}\]. The correct reason for higher \[B-F\] bond dissociation energy as compared to that of \[C-F\] is

A) stronger a bond between B and F in \[B{{F}_{3}}\]as compared between C and F in\[C{{F}_{4}}\].

B) significant \[p\pi -p\pi \] interaction between B and F in \[B{{F}_{3}}\]whereas there is no possibility of such interaction between C and F in\[C{{F}_{4}}\].

C) lower degree of \[p\pi -p\pi \] interaction between B and F in \[B{{F}_{3}}\]than between C and F in\[C{{F}_{4}}\].

D) smaller size of B- atom as compared to C- atom.

Correct Answer: B

Solution :

The delocalised bonding between filled p-orbital of F and vacant p-orbital of B leads to shortening of B-F bond length which results in higher bond dissociation energy of the B-F bond.