Tue February 07, 2012 By:

Explain "p pie-p pie" and "d pie-p pie' bond.

Expert Reply
Thu February 09, 2012
Back-bonding  is  the  special  type  of  bond which  is  formed between sp  hybridised  central atom which must  have empty  p-orbital .  Due  to  this  empty p-orbital it  pulls the  electron  from the  another  p-orbital which is  near by  it .  This  type  of  bond  formation is  known  as  back bonding  or  p?  -p? bond.
Due  to  the  presence  of  empty  p-orbital molecule  have  tendency  to  attaract the pair of  electron & the  species which  attract  the  pair  of  electron is  termed  as  lewis  acid .  among  BF3   BCL3   BBR3   BI3  this  type  of  bonding  is  found .  all  these  are  electron deficient  molecules. So  they  must  be  acidic  but  in  BF3  the  electron deficiency  of  boron  is  vanished  hence  electron  attracting  tendency  of  boron  will  be  least. This makes BF3   a  weak  acid.
Similarly, d ?-p ? is also an example of back bonding. This is commonly seen in metallic compounds.
Both ? bonds in XeO2F2 are of type is d ? (OF XENON) p ? (of oxygen).The reason is hybridisation of Xe in compound is sp3d . so no chance of p ? p ? bonds(all 3 p orbitals of Xe are used in hybridisation) it has 2 d ? p ? bonds.
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