Heterolytic Bond Cleavages

HETEROLYTIC BOND CLEAVAGES

Simple bond cleavages can proceed with the shared pair ultimately residing on either of the previously joined elements. In either case one atom has a sextet electronic structure and a positive charge. The other has a valence octet with at least one lone pair (the pair that was formerly shared) and a negative charge. Such bond cleavage, in which the previously shared pair goes with one of the bonded atoms, is termed heterolytic cleavage and necessarily results in the formation of charged species.

In general, the movement of electrons during heterolytic cleavage follows the direction of bond polarity. In a polar covalent bond the shared pair is displaced toward the more electronegative element. Upon cleavage the pair of bonded electrons are transferred completely to the more electronegative element, which becomes negatively charged, and the more electropositive element loses the bonded electron pair and becomes positively charged.

If one of the bonded elements is positively charged to begin with, it can gain the bonded pair upon bond cleavage and become neutral. Note, however, that net charge is always conserved in any reaction. Moreover, bond cleavages are depicted the same whether they involve σ or π bonds.