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 \[\sigma \] bond between B and F in\[~B{{F}_{3}}\] as compared to that 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 that between C and F in \[C{{F}_{4}}\]

D) Smaller size of \[B-atom\] as compared to that of C-atom.

Correct Answer: B

Solution :

[b] The delocalised \[p\pi -p\pi \] 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.