Question

Arrange the following in the correct order of Lewis acidity: BF₃, BCl₃, BBr₃.

• A. BF₃ > BBr₃ > BCl₃
• B. BF₃ > BCl₃ > BBr₃
• C. BF₃ < BCl₃ < BBr₃
• D. BBr₃ < BF₃ < BCl₃

Answer 1

Answer: (C)

In BF₃, BCl₃ and BBr₃ each will shown ${\text{p}}_{\pi }-{\text{p}}_{\pi }$ back bonding as follows.



Extant of overlapping as the $2\text{p}-2\text{p}>2\text{p}-3\text{p}>2\text{p}-4\text{p}$ difference between the size of p orbital increases the extent of overlapping decreases the availability of vacant orbital increases and the acidic character increases.

Hence correct order of Lewis acidity represented by option (BF₃ < BCl₃ < BBr₃) .