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:
“In England and America a beard usually means that its owner would rather be considered venerable than virile; on the continent of Europe it often means that its owner makes a special claim to virility.”
—Rebecca West (1892–1983)
“There are few cases in which mere popularity should be considered a proper test of merit; but the case of song-writing is, I think, one of the few.”
—Edgar Allan Poe (1809–1845)