Question

The correct statement(s) regarding diborane is/are :

• A. Maximum six hydrogen atoms can lie in a plane
• B. Maximum six atoms can lie in a plane
• C. Bridging $H_b-B-H_b$ bonds are stronger than terminal $B-H_t$ bonds
• D. Terminal $H_t-B-H_t$ bond angle is greater than bridging $H_b-B-H_b$ bond angle.

Answer 1

Answer: (B), (C), (D)

Terminal $H_t-B-H_t$ bond angle is greater than bridging $H_b-B-H_b$ bond angle.

a) In diborane, both boron are tetravalent hence $s{p}^3$ hybridized .So terminal hydrogen lies in one plane and other two hydrogen (bridge hydrogens) lie above and below the plane. Therefore only four hydrogens out of six hydrogen lies in one plane.

b) The two boron atoms and the four terminal hydrogen atoms lie in the same plane . Hence maximum six atoms can lie in a plane.

c) The bridging hydrogen bonds are stronger because the bridging $H$-atoms can not be replaced in chemical reactions whereas terminal $H$ atoms can be replaced in chemical reaction. For example in methylation reaction.

d) The terminal $H_t-B-H_t$ bond angle is around ${120}^o$ and bridging $H_b-B-H_b$ bond angle is around ${97}^o$. So, terminal $H_t-B-H_t$ bond angle is greater than bridging $H_b-B-H_b$ bond angle.

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