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Describe the structure of diborane. |
Answer» Solution :In doborane two `BH_(2)` units are linked by two BRIDGED hydroens. Therefore, it has EIGHT B-H bonds. However, diborane has only 12 valance electrons and are not sufficient to form NORMAL covalent bonds. The four terminal B-H bonds are normal covalent bonds (two centre- two electron bond or 2 c-2e bond). THe remianing four electrons have to used for the bridged bonds. i.e. two three centred B-H-B bonds utilise two electrons each. Hence, these bonds are three centre two electron bonds. THe bridging hydrogen atoms are in a plane as shown in the figure. In diborne, teh boron is `sp^(3)` hybrodised. Three of the four `sp^(3)` hybrodised orbitals contains single electron and the fourthorbital is EMPTY. Two of the half filled hybridised orbitals of each boron overlap wit the two hydrogens to form four terminal 2c-2e bonds, leaving one empty and one half filled hybridised orbitals on each boron. THe three centre two electron bonds, B-H-B bond formation involves overlapping the half filled hybridised orbital of one boron, the empty hybridised orbital of the other boron and the half filled 1S orbital of hydrogen. 
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