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| 1. |
Why BBr_(3) is a strongerLewis acid as compared to BF_(3) throughflorine is more electronegative than bromine ? |
| Answer» Solution :The B atom in `BF_(3)`or `BBr_(3)`has only six electron inits valenceshell andhence can accepta pair ofelectronsto completeits octet.Therefore,both `BF_(3)` and `BBr_(3)` at as Lewisacids. But in `BF_(3)`,the sizes of empty `2p-`orbitalof B ANDTHE 2p-orbital ofF containing thelone pairof electronsare almostidenticaland henceeffective `ppi - ppi`boundingoccurs. As aresult,the lone pair of F is donate to Batom and hence the electrons deficiencyof borondecreases. Incontrast, in `BBr_(3)`.the size of 4p-orbitalov Br containingthe lone pair of electronsis much bigger than the empty 2p-orbitalof Band hencedonationof lone pairof electronsof Br toB does not occurto an significationextent. As a result, the electron deficiencyof B is much higherto `BBr_(3)`than in `BF_(3)`, and hence`BBr_(3)` i a stronger Lewisand than `BF_(3)`. | |