Table 6. Stabilization energies of selected donor–acceptor interactions derived from the second order perturbation analysis of the NBO's of Na-1, Na-2 and Na-3 .
| Comp. | Donor NBO | Acceptor NBO | Energy [kcal mol–1] | Torsion angle b [°] |
| Na-1 | LP (C) | σ* (Si–CHA3) | 5.0 | 45 |
| LP (C) | σ* (Si–CHB3) | — a | 80 | |
| LP (C) | σ* (Si-OR) | 14.9 | 165 | |
| Na-2 | LP (Si) | σ* (Si–CHA3) | 1.2 | 50 |
| LP (Si) | σ* (Si–CHB3) | — a | 70 | |
| LP (Si) | σ* (Si-OR) | 11.2 | 170 | |
| Na-3 | LP (Ge) | σ* (Si–CHA3) | — a | 45 |
| LP (Ge) | σ* (Si–CHB3) | — a | 75 | |
| LP (Ge) | σ* (Si-OR) | 6.6 | 165 |
a Below the threshold of 0.5 kcal mol–1.
b Estimated torsion angles for LP-E–Si–CH3 or LP-E–Si–OR, where E = C, Si or Ge and LP = lone pair.