The bond dissociation energy of B – F in BF3 is 646kJ mol^–1 whereas that of C – F in CF4 is 515kJ mol^–1.

Monjur Alahi

The bond dissociation energy of B – F in BF3 is 646kJ mol–1 whereas that of C – F in CF4 is 515kJ mol–1. The correct reason for higher B – F bond dissociation energy as compared to that of C – F is
(a) smaller size of B-atom as compared to that of C-atom

(b) stronger σ bond between B and F in BF3 as compared to that between C and F in CF4

(c) significant pπ-pπ interaction between B and F in BF3 whereas there is no possibility of such interaction between C and F in CF4.

(d) lower degree of pπ-pπ interaction between B and F in BF3 than that between C and F in CF4.


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Salim Ahmed Kawsar

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(c) : In BF3, B is sp2 hybridised and has a vacant 2p-orbital which overlaps laterally with a filled 2p-orbital of F forming strong pp-pp bond. However in CF4, C does not have any vacant p-orbitals to undergo p-bonding. Thus B.E.B – F > B.E.C – F.

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