CHEM 121 glossary
π bond (pi bond)
A covalent bond formed by side-on overlap of two parallel, unhybridized p orbitals, with electron density above and below the bond axis and a nodal plane containing the axis. A double bond is 1σ + 1π and a triple bond 1σ + 2π; the π bond is weaker than the σ bond and blocks rotation about the bond.
Side-on overlap of parallel p orbitals: density above and below the axis.
Example
(N≡N) has one σ and two π bonds, the two π bonds at right angles to each other. Because a π bond blocks rotation, cis- and trans-2-butene () are two different compounds that do not interconvert at room temperature.