Chemical Bonding and Molecular Structure

Chemical Bonding and Molecular Structure

Question

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

  • Smaller size of B-atom as compared to that of C- atom

  • Stronger σ bond between B and F in BF3 as compared to that between C and F in CF4

  • Significant pπ - pπ interaction between B and F in BF whereas there is no possibility of such 3 interaction between C and F in CF4 

  • lower degree of pπ - pπ interaction between B and F in BF3 than that between C and F in CF4

Answer

C.

Significant pπ - pπ interaction between B and F in BF whereas there is no possibility of such 3 interaction between C and F in CF4 

B has vacant available p orbital and hence it involves pπ - pπ back bonding which is not possible in CF4 as C does not have vacant orbital. 

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