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Sunday, January 3, 2021

Why methylation of Diborane (B2H6) replace four hydrogen only ?

Methylation of Doborane:

(1) In diborane two boron atoms and four terminal hydrogen atoms lie in one plane. While two bridge hydogen atoms (encircled ) lie smmetrically above and below the plane.

(2) Total valence electrons in B2H6 is 12(6 from boron 3x2) and 6 from six hydrogen atoms) and there are two B-H-B (3C-2e) bridge bonds and four B-H (2C-2e) terminal bonds.

(3) Bond energy of B-H-B bond is 441 kj per mole which greater than bond energy B-H bond (341Kj per mole) hence methylation of diborane no more than four hydrogen.

(4) In above reaction it is clearly reveal that none of the bridge hydrogen in B2H6  has been replaced by –CH3 .ie in this reaction both the bridge bond remaine undissociate.

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