Q.Describe the structure of diborane.

Step 1. Diborane, B₂H₆, has two BH₂ units joined by two bridging hydrogen atoms, giving eight B-H bonds in total.

Step 2. But diborane's 12 total valence electrons are not enough to form eight ordinary two-electron covalent bonds, which would need 16 electrons -- diborane is therefore an electron-deficient molecule.

Step 3. The four terminal B-H bonds (two per boron, pointing outward) are ordinary two-centre-two-electron (2c-2e) bonds, accounting for 8 of the 12 electrons.

Step 4. The remaining 4 electrons are shared between the two bridging B-H-B bonds; because each spans three atoms (bridging H plus both borons) using only 2 electrons, each is a three-centre-two-electron (3c-2e) bond, popularly called a 'banana bond'. The two bridging hydrogens lie in the same plane. …

Count diborane's total valence electrons, split them between the four terminal 2c-2e bonds and the two bridging 3c-2e bonds, then des …

• Trying to draw diborane with eight ordinary two-electron bonds -- this would need 16 valence electrons, but diborane has only 12, which is exactly why the bridging bonds mu …