beckmann

which cant be used in beckmann rearrangemt

a) TsOH
b) R-SO₂Cl
c) BF₃
d) Ph-Li

1 Answers

beckmann rearrangemt is normally an acid catalsed rearrangement of oxime. as u know, in the first

step , dehydration i.e. more precisely , the removal of -OH group takes place. but, -OH is a bad

leaving group. so, the reagent used should enhance the leaving capability of -OH group. Now,

observing the options, Tosyl group when attached to any group , makes it a very good leaving

group. Next , R-SO₂Cl is a lewis acid and it enhances the leaving capability of -OH group by

accepting its lone pair. BF3 too is a lewis acid with incomplete octet.

thus ans is d)

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