Question

Why is diborane classified as electron deficient compound?

Answer 1

Diborane is said to be electron deficient because boron require 5 electrons to complete its octet. But in this molecule, each boron atom is bonded to 2 terminal hydrogen atoms each. Also, the two boron atoms are held together by two hydrogen atoms as shown below: ... Thus, it is an electron deficient molecule.

Answer 2

Diborane is said to be electron deficient because, boron has five electrons at its outermost shell. So, in this molecule each boron atom uses two of its valence electrons to bond with two terminal hydrogen atoms. Therefore, it lefts with one valence electron and the bridging hydrogen atom provide one electron each.