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Is BI3 a stronger Lewis acid than BCl3 and BF3? Why?

In boron halides, there exists certain degree of  pi bonding involving halogen lone pairs and empty 2p orbital of boron.This bonding is strongest in case of BF3 and when a boron halide accepts electrons from a donor molecule, this bonding is lost. Due to this, BF3 resists this change most strongly followed by other halides and thus the acceptor strength increases in the order BF3 < BCl3 < BBr3 < BI3

Due to this, BI3 a stronger Lewis acid than BCl3 and BF3

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Borontrihalides arelewis aciddue to sextet of electrons ....BI3 is stronger lewis acid ...and acidic order is BI3 BBr3 BCl3 BF3lets start with BF3 ....due to back bonding means electron donation by fluorine to boron ....electron density increases in boron and hence its lewis acid character decreases....now one might wonder why F being most electronegative donates its lone pair to boron ....the reason is it do so because in order to achieve octet around boron which gives stability to molecule ....weird but true .....i wonder why chemistry is not like maths where there isnt any exceptionas we move from fluorine to chlorine size of orbitals increases and hence there isnt much effective back bonding in BCl3 as compared to BF3 .....similarly BBr3 will have less back bonding due to much greater increases in size of overlapping orbitals .....and so on ....so as tendency of back bonding decreases from F to I ....lewis acid character increases from F to I

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