4
Question
Why is boron trifluoride written in two ways in the Lewis dot diagram structure ?
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Solution
Answer
Because experiments suggest that there is some degree of overlap....
Explanation :
So BF3 versus +F=B−−F2 ; note the formal charges on the boron and fluorine centres. Why should we represent it this way? Well, it is a fact that BBr3 is THE STRONGEST LEWIS KNOWN. Why? Because the degree of overlap, i.e. backbonding, between boron and bromine is miniscule given the relative size of the boron and bromine centres. On the other hand, with BF3, the fluorine lone pairs are the right size and right symmetry to overlap with the empty boron p orbital.
Of course,BF3 is still a Lewis acid, and in fact you can form ET2OBF3, boron trifluoride etherate, as a distillable liquidBX3(X=Cl,Br) tend to be so Lewis acidic that they rip up (i.e. react with) added ethers.
Many boron chemists use such reagents as Me2NBCl2 , and they tend to depict the molecule as Me2N+=B−Cl2 by invoking a formal N = B bond.
Because experiments suggest that there is some degree of overlap....
Explanation :
So BF3 versus +F=B−−F2 ; note the formal charges on the boron and fluorine centres. Why should we represent it this way? Well, it is a fact that BBr3 is THE STRONGEST LEWIS KNOWN. Why? Because the degree of overlap, i.e. backbonding, between boron and bromine is miniscule given the relative size of the boron and bromine centres. On the other hand, with BF3, the fluorine lone pairs are the right size and right symmetry to overlap with the empty boron p orbital.
Of course,BF3 is still a Lewis acid, and in fact you can form ET2OBF3, boron trifluoride etherate, as a distillable liquidBX3(X=Cl,Br) tend to be so Lewis acidic that they rip up (i.e. react with) added ethers.
Many boron chemists use such reagents as Me2NBCl2 , and they tend to depict the molecule as Me2N+=B−Cl2 by invoking a formal N = B bond.
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