The bond dissociation energy of `B-F` in `BF_(3)` is `"646 kJ mol"^(-1)` whereas that of `C-F` in `CF_(4)` is `"515 kJ mol"^(-1)`. The correct reason for higher `B-F` bond dissociation energy as compared to that of `C-F` is

Options

A. stronger `sigma`-bond between B and F in `BF_(3)` as compared to that between `C` and `F` in `CF_(4)`
B. significant `ppi-ppi` interaction between B and F in `BF_(3)` whereas there is no possibility of such interaction between C and F in `CF_(4)`
C. lower degree of `ppi-ppi` interaction between B and F in `BF_(3)` than that between C and F in `CF_(4)`.
D. smaller size of B-atom as compared to that of C-atom

Answer

B

Explanation

Due to identical size of 2p-orbitals on B and F, back donation of a lone pair of electrons from the filled 2o-orbitals of F to the empty 2p-orbital of B occurs to a considerable extent. As a result , `B-F` bond has some double character and hence bond dissociation energy of `B-F` bond in `BF_(3)` is much higher than that of C-F bond in `CF_(4)`. the reason being that C does not have an empty 2p-orbitals and hence back donation does not occur.