Question

The tendency of BF₃ , BCl₃ and BBr₃ to behave as Lewis acid decreases in the sequence:

(a) BCl₃ > BF₃ > BBr₃

(b) BBr₃ > BCl₃ > BF₃

(c) BBr₃ > BF₃ > BCl₃

(d) BF₃ > BCl₃ > BBr₃

Answer 1

Correct option:b) BBr₃ > BCl₃ > BF₃

Explanation:

p-p overlap between B and F is maximum due to identical size and energy of porbitals, so electron deficiency in boron of BF₃ is neutralized partially to the maximum extent by back donation.

Hence BF₃ is least acidic.