Quantum-chemical investigation of allyl compounds of group IV elements. 2. Electron absorption spectra

Conclusions

• 1. A breach is coplanarity in allyl compounds of silicon, germanium, tin, and lead results in a modification and mixing of the upper occupied MO of the π and σ types, and to an increase in the energy gap between them. The same situation occurs with two lower vacant MO. The energy of quasilocal electron transitions, π → π* and σ → σ*, remains practically unchanged in this case, and the energy of the transition with charge transfer π-σ* decreases significantly. The maximum longwave displacement of this absorption band takes place in the gauche conformer.

• 2. The root cause of the intensification degree of the modification of MO and of electron absorption spectra when passing to allyl compounds with heavier atoms is the closer approach in the position on the scale of energies of boundary a and σ* MO of the CH₂-XH₃ group.