LONE-PAIR LONE-PAIR INTERACTIONS

The lone-pair ionisation potentials of the halogens, disulphides and h ydrazines are analysed by a simple MO procedure including orbital over lap. Calculations of Slater overlap integrals for adjacent sp2 and sp3 orbitals show that the energy of the cis isomer is lower than the ene rgy of the trans in the former case but the reverse in true for sp3 hy bridised orbitals. Gaussian overlap integrals are greater for the tran s form than for the cis, both for sp3 and sp2 nitrogen orbitals. Exper imental evidence in support of these conclusions for sp2 systems is to be found in the greater stability of the Z isomers of sulphonylamines and sulphur diimides.