Special Cases
Pi bonds do not necessarily connect a pair of atoms that are also sigma-bonded.
In certain metal complexes, pi interactions between a metal atom and alkyne and alkene pi antibonding orbitals form pi-bonds.
In some cases of multiple bonds between two atoms, there is no sigma bond at all, only pi bonds. Examples include diiron hexacarbonyl (Fe2(CO)6), dicarbon (C2), and the borane B2H2. In these compounds the central bond consists only of pi bonding, and in order to achieve maximum orbital overlap the bond distances are much shorter than expected.
Read more about this topic: Pi Bond
Famous quotes containing the words special and/or cases:
“The rebellion is against time pollution, the feeling that the essence of what makes life worth living—the small moments, the special family getaways, the cookies in the oven, the weekend drives, the long dreamlike summers Mso much of this has been taken from us, or we have given it up. For what? Hitachi stereos? Club Med? Company cars? Racquetball? For fifteen-hour days and lousy day care?”
—Richard Louv (20th century)
“You all know that even when women have full rights, they still remain fatally downtrodden because all housework is left to them. In most cases housework is the most unproductive, the most barbarous and the most arduous work a woman can do. It is exceptionally petty and does not include anything that would in any way promote the development of the woman.”
—Vladimir Ilyich Lenin (1870–1924)