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Which of the following is the electron deficient molecule -
A
$C_2H_6$
B
$SiH_4$
C
$PH_3$
D
$B_2H_6$
Detailed Solution
An electron deficient molecule does not have enough valence electrons to form normal two-centre two-electron bonds between all its bonded atoms.
Diborane, $B_2H_6$, has only 12 valence electrons (3 from each B and 1 from each H), but it would need 14 electrons to form seven normal B-H and B-B bonds.
Its structure has four terminal B-H bonds (normal two-electron bonds) and two bridging B-H-B bonds, each of which is a three-centre two-electron (banana) bond.
So diborane is an electron deficient molecule and acts as a Lewis acid.
$C_2H_6$, $SiH_4$ and $PH_3$ have normal electron-precise bonds (and $PH_3$ is electron rich, with a lone pair).
So the electron deficient molecule is $B_2H_6$.
Diborane, $B_2H_6$, has only 12 valence electrons (3 from each B and 1 from each H), but it would need 14 electrons to form seven normal B-H and B-B bonds.
Its structure has four terminal B-H bonds (normal two-electron bonds) and two bridging B-H-B bonds, each of which is a three-centre two-electron (banana) bond.
So diborane is an electron deficient molecule and acts as a Lewis acid.
$C_2H_6$, $SiH_4$ and $PH_3$ have normal electron-precise bonds (and $PH_3$ is electron rich, with a lone pair).
So the electron deficient molecule is $B_2H_6$.