Compound X onreductionwith LiAlH_(4) givesa hydride Y containing 21.72% hydrogenalong withother products. The compound Y reactswith airexplosively resultingin borontrioxide. Identify Xand Y. Givebalancedequations involved in the formation of Y and its reactionwith air. Drew thestructure of Y.

Compound X onreductionwith LiAlH_(4) givesa hydride Y containing 21.72

1.	Compound X onreductionwith LiAlH_(4) givesa hydride Y containing 21.72% hydrogenalong withother products. The compound Y reactswith airexplosively resultingin borontrioxide. Identify Xand Y. Givebalancedequations involved in the formation of Y and its reactionwith air. Drew thestructure of Y.
Answer» Solution :Step 1. To determine the molecular formulaand structureof compound Y. (i) Since the hydride Y reacts with airforming boron TRIOXIDE, Therefore, `Y` must be an hydrideof boron. (ii)`%H = 21.72%` (Given) `:. %B = 100-21.72 = 78.28%` Now, `B : H = (78.28)/(11) :(21.72)/(1)= 7.12:21.72 = 1: 3 , :. E.F. " of "Y = BH_(3)` Since boron forms two types of hydrides, i.e., `B_(n)H_(n+4)` (nidoboranes) and `B_(n)H_(n+6)` (arachnoborans), therefore Y must bea nidoboranewith `n = 2`. Thus, M.F. of `Y = B_(2)H_(6)`. It Y is `B_(2)H_(6)` (diborane), then its structuremust be as follows : Bridges `B"........."H = 134` pm Terminal `B "______" = 119` pm Step 2. To determine the structureof the compound X. Since compound T i.e, `B_(2)H_(6)` is formedby reduction of compound X with `LiAlH_(4)`, therefore , X musteither `BCl_(3)` or `BF_(3)`. `underset(X)(4BF_(3)) + 3LiAlH_(4) overset("other")rarr underset(Y)(2B_(2)H_(6)) + 3LiAlF_(4)` The equation representing the reaction of Y with `O_(2)` maybe written as follows : `underset("Diborane",Y)(B_(2)H_(6)) + 3O_(2)rarr underset("Boron trioxide")(B_(2)O_(3)) +3H_(2)O` Thus, `X = BF_(3)` and `Y = B_(2)H_(6)`.