Question

Which one of the following statements is not true regarding diborane ?

• A. It has two bridging hydrogens and four perpendicular to the rest.
• B. When methylated, the product is $M{e}_4{B}_2{H}_2.$
• C. The bridging hydrogens are in a plane perpendicular to the rest.
• D. All the B - H bond distances are equal.

Answer 1

The correct option is D All the B - H bond distances are equal.

Diborane is an electron deficient compound. In diborane, total number of valence electrons is 12. Diborane contains two coplanar $B{H}_2$ groups. Diborane has four terminal hydrogen atoms and the two boron atoms lie in one plane. Above and below this plane, there are two bridge hydrogen atoms. The bridge hydrogen atoms are present in a plane perpendicular to rest of the molecule. Each bridge hydrogen is bonded to the two boron atoms only by sharing of two electrons. These are called three centred two electron ($3c-2e$) bonds, also known as banana or tau bonds. Methylation test of diborane is done which confirms the presence of two bridged hydrogen atom. Diborane cannot be methlated beyond $M{e}_4{B}_2{H}_2$.