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 :

JEE Main 2009 Chemistry question

The bond dissociation energy of B − F in is 646 kJ whereas that of C − F in is 515 kJ . The correct reason for higher B-F bond dissociation energy as compared to that of is :

(1)smaller size of B-atom as compared to that of C- atom
(2)stronger σ bond between B and F in as compared to that between C and F in
(3)significant interaction between B and F in whereas there is no possibility of such interaction between C and F in .Correct
(4)lower degree of interaction between B and F in than that between C and F in .

Answer: (3)

Solution

In , boron has a vacant 2p orbital that accepts lone-pair density from fluorine ( back bonding), giving partial double-bond character

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Question ID VK-039148