Question

The structure of diborane $\left(B_2{H}_6\right)$ contains:

• A. Four $(2C–2e^{–})$ bonds and two $(2C–3e^{–})$ bonds
• B. Four $(2C–2e^{–})$ bonds and two $(3C–2e^{–})$bonds
• C. Four $(2C–2e^{–})$ bonds and four $(3C–2e^{–})$bonds
• D. None

Answer 1

The correct option is B Four $(2C–2e^{–})$ bonds and two $(3C–2e^{–})$bonds

According to molecular orbital theory, each of the two boron atoms is in sp${}^3$ hybrid state. Out of the four hybrid orbitals, three have one electron each while the fourth is empty. Two of the four orbitaIs of each of the boron atom overlap with two terminal hydrogen atoms forming two normal B–H $\sigma$-bonds. One of the remaining hybrid orbital (either filled or empty) of one of the boron atoms, 1s orbital of hydrogen atoms (bridge atom) and one of hybrid orbitaIs of the other boron atom overlap to form a delocalised orbital covering the three nuclei with a pair of electrons. Such a bond is known as three centre two electron $(3C–2e^{-})$ bonds.

So, diborane contains four $(2C–2e^{–})$ bonds and two $(3C–2e^{–})$ bonds.