MCQ
Correct order of Lewis Acidic strength?
- ✓$BF_3 < BCl_3 < BBr_3 < BI_3$
- B$BF_3 > BCl_3 > BBr_3 > BI_3$
- C$BF_3 = BCl_3 = BBr_3 = BI_3$
- D$BF_3 > BCl_3 < BBr_3 > BI_3$
✓
Answer
Correct option: A.
$BF_3 < BCl_3 < BBr_3 < BI_3$
a
(i) On the basis of back bonding, smaller be the halide atom, more effective be the back bonding and show less tendency to accept a pair of electrons.
(i) On the basis of back bonding, smaller be the halide atom, more effective be the back bonding and show less tendency to accept a pair of electrons.
(ii) Size of halides increase down the group, hence the ability of back bonding decreases making the molecule more acidic.
Hence, correct order of Lewis acid for boron-halides is $\mathrm{Bl}_{3}>\mathrm{BBr}_{3}>\mathrm{BCl}_{3}>\mathrm{BF}_{3}$
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