Which of the following statements are correct ? Answer on the basis of given figure

Options

A. The two bridged hydrogen atoms and the two boron atoms lie in one plane
B. Out of six B-H bonds two bonds can be described in terms of 3 centre 2 electron bonds
C. Out of six B-H bonds four B-H bonds can be described in terms of 3 centre 2 electron bonds
D. The four terminal B-H bonds are two centre-two electron regular bonds

Answer

A, B, D

Explanation

The bonding and strcuture of the boranes are of great interest. They are different from all other hybrides as they are electron deficient
In diborane, there are 12 valence electrons, three from each B-atom and six from H-atoms. Electron structure shown in figure

The two bridging H-atoms are in a plane perpendicular to the rest of the molecule and prevent rotation between the two B-atoms
The terminal B-H distances are the same as the bond lengths measured in non-electron dificient compounds. These are assumed to be normal covalent bonds, with two electrons shared between two atoms. We can describe these bonds are two centre two electron bond (2c-2e)
Obviously, they are abnormal bonds are as the bridges involve only one electron each from one of the boron atoms adn hydrogen atoms, making a total of four electrons. According to molecular orbital theory, each B-atom uses `sp^(3)`-hybrid orbitals for bonding. Out of the four `sp^(3)`-hybrid orbitals on each B-atom, one is with out an electron shown in broken lines.
The terminal B-H bonds are normal 2 centre-2 electron bonds but the two bridge bonds are 3 centre-2 electron bonds. The 3-centre-2 electron bridge bonds are also called banana bonds.
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