Which is correct for the structure of diborane ?

Options

A. four `2C-2e^(-)` bonds and four `3C-2e^(-)` bonds
B. two `2C-2e^(-)` bonds and two `3C-2e^(-)` bonds
C. two `2C-2e^(-)` bonds and four `3C-2e^(-)` bonds
D. four `2C-2e^(-)` bonds and two `3C-2e^(-)` bonds

Answer

D

Explanation

Each of the two `B` atoms is in `sp^(3)` hybrid state. Of the four hybrid orbitals, three have one electron each while the fourth is empty. Two of the four hybrid orbitals of each of the `B` atoms overlap with two terminal `H` atoms forming two normal `B-H sigma` bonds (a total of four `2C-2e^(-)` bonds), one of the remaining hybrid orbital (either filled or empty) of one of the `B` atoms, `1s`-orbital of `H` atom (bridge atom), and one of the hybrid orbitals of another `B` atom overlap together to form a delocalized orbital covering the three nuclei with a pair of electrons. Such a bond is known as three-center two-electron bond (a total of two `3C-2e^(-)` bonds).