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Monday, January 18, 2021

What is structure of diborane?

(1)  B2H6 contains 4-Terminal H are bonded by Sigma bond and  remaining 2-H are bridging hydrogen's and of these are broken then dimer become monomer.

(2) Boron undergoes sp3 hybridisation 3 of its sp3 hybridised orbitals contain one( e¯) each and fourth sp3 hybrid orbital is vacant.

(3) 3-(Three) of these sp3 hybrid orbitals get overlapped by s orbitals of 3-hydrogen atoms.

(4) One of the sp3 hybrid orbitals which have been overlapped by s orbital of hydrogen gets overlapped by vacant sp3 hybrid orbital. Of 2nd Boron atom. And it's vice versa.

(5) By this two types of overlapping take place 4 (sp3– s) overlap bonds and 2(sp2 – s – sp3) overlap bonds.

(6) H is held in this bond by forces of attraction from B and This bond is called 3 centred two electron bonds (3C-2e bond) . Also called Banana bonds. Due to repulsion between the two hydrogen nuclei, the delocalised orbitals of bridges are bent away from each other on the middle giving the shape of banana.

(7) The two bridging hydrogens are in a plane and perpendicular to the rest four hydrogen atoms.


(A) 4 bridged hydrogens and two terminal hydrogen are present

(B) 2 bridged hydrogens and four terminal hydrogen are present

(C) 3 bridged and three terminal hydrogen are present

(D)None of the above


ILLUSTRATED EXAMPLE (2): 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 Me4B2H2.

(C) The bridging hydrogens are in a plane and perpendicular to the rest.

(D ) All the B–H bond distances are equal


ILLUSTRATED EXAMPLE (3): The structure of diborane (B2H6) contains

(A) Four (2C–2e–) bonds and two (2C–3e–) bonds

(B) Two (2C–2e–) bonds and two (3C–2e–) bonds

(C) Four (2C–2e–) bonds and four (3C– 2e–) bonds

(D ) None of these

ILLUSTRATED EXAMPLE (4): The molecular shapes  of diborane is shown:

Consider the following statements for diborane:

1. Boron is approximately sp3 hybridised

2. B–H–Bangle is 180°

3. There are two terminal B–H bonds for each boron atom

4. There are only 12 bonding electrons available

Of these statements:

(A ) 1, 3 and 4 are correct                  (B) 1, 2 and 3 are correct

(C) 2, 3 and 4 are correct                    (D) 1, 2 and 4 are correct

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