109 Polar and radical reactions
109.0.1 Homolytic vs heterolytic cleavage
Two bonded atoms can come apart from each other in one of two ways. Either
1.each atom gets away with half of the shared electrons, or
2.one of the atoms leaves with more of the shared electrons than the other.In homolytic cleavage, each atom leaves with one-half of the shared electrons (one
electron for a single bond, or two for double bonds).
A—B --> A + B
A and B represent uncharged radicals. The ”*” represents an unbonded, unpaired valence electron.
Inheterolytic cleavage, one atom leaves with all of the previously shared electrons and
the other atom gets none of them.
A—B --> A-+ B+
sameindicates that each atom leaves with the same number of electrons from the bond.
different, refers to the fact that the atoms each end up with a different number of electrons.
109.1 Polar reactions
Polar reactionsoccur when two bonded atoms come apart, one taking more of the shared
electrons than the other. They involveheterolytic cleavage. The result is two charged
species—one cation and one anion.
109.2 Radical reactions.
Radical reactions don’t deal with charged particles but with radicals. Radicalsare
uncharged atoms or molecules with an incomplete octet of valence electrons.
When a molecule comes apart byhomolytic cleavagethe result is two radicals. Although
uncharged, radicals are usually very reactive because the unfilled octet is unstable and the
radical can lower its energy by forming a bond in a way that allows it to fill its valence shell
while avoiding any electrostatic charge..