Verified Solution • 2025–26 Session moderate

QJEEM08Ch634f: JEE Main 2008 Chemistry - Class 11 JEEM08Ch634f Solution: The bond dissociation energy of B - F in BF 3 is 646 kJ mol -1…

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

Multiple Choice Options

  • 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.

Step-by-Step Verified Solution

In BF3, B is sp2 hybridised and by Back Bonding method strong pπ-pπ bond is created between filled p-orbital of F and vacant p-orbital of B which leads to shortening of B–F bond length which results in higher bond dissociation energy of the B–F bond. However in CF4, C does not have any vacant p-orbitals to undergo π-bonding.

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