Question

Compound (X) on reduction with LiAlH₄ gives a hydride (Y) containing 21.72% hydrogen along with other products. The compound (Y) reacts with air explosively resulting in boron trioxide. Identify (X) and (Y). Give balanced reactions involved in the formation of (Y) and its reaction with air. Draw the structure of (Y).

Answer 1

Compound `X’   `Y’ [which contains 21.72% hydrogen and other products]

Compound `Y’ + O₂ (air) → B₂O₃ 

Therefore compound `Y’ is hydride of boron and it is obtained by the reduction of `X’ with LiAlH₄. Hence, X is BCl₃. 

Now,

Mol. wt. of compound Y (B₂H₆) = 21.76 + 6 = 27.76

Structure of Y (B₂H₆)

In this case, two electrons of a B-H bond are involved in formation of three center bond (Banana bond) these two bonds are represented by dotted lines in figure, in which one lies above and second lies below to the main plane.