The bond dissociation energy of B – F in BF3 is 646 kJ mol–1 whereas that of C – F in CF4 is 515 kJ mol–1. The correct reason for higher B – F bond dissociation energy as compared to that of C – F is
(a) stronger σ bond between B and F in BF3 as compared to that between C and F in CF4.
(b) significant pπ – pπ interaction between B and F in BF3 whereas there is no possibility of such interaction between C and F in CF4.
(c) lower degree of pπ – pπ interaction between B and F in BF3 than that between C and F in CF4.
(d) Smaller size of B-atom as compared to that of C-atom
Correct answer: (b) significant pπ – pπ interaction between B and F in BF3 whereas there is no possibility of such interaction between C and F in CF4.
Explanation:
The delocalised pπ – pπ 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.