Table 7.
NBO parameters for conformers of compounds 3 and 4, calculated at the ωB97X-D/aug-cc-pVTZ level of theory. Relative energy of the steric (Erel,Lewis) and hyperconjugative (Erel,Hyper) interactions are given in kcal mol−1. The sum of Erel,Lewis and Erel,Hyper is the total energy of the system.
| conformation | CHCl3 | DMSO | nO→σ*N–H a | nO→σ*S–H a | ||
| Erel,Lewis | Erel,Hyper | Erel,Lewis | Erel,Hyper | |||
| 3-trans-Ia | 7.47 | 8.65 | 5.19 | 5.90 | 0.98 | – |
| 3-trans-IIc | 3.13 | 3.63 | 3.11 | 3.91 | – | – |
| 3-trans-IIIc | 1.17 | 1.44 | 0.16 | 0.35 | – | – |
| 3-trans-IVc | 0.00 | 0.00 | 0.00 | 0.00 | – | – |
| 3-trans-Vb | 3.85 | 3.75 | 0.92 | 0.39 | 0.70 | – |
| 3-cis-VIa | – | – | 4.63 | 4.12 | – | – |
| 4-trans-Ia | 2.32 | 2.72 | 3.14 | 2.54 | 1.03 | – |
| 4-trans-IIb | 0.00 | 0.00 | 0.00 | 0.00 | – | – |
| 4-trans-IIIb | 3.86 | 1.63 | 5.94 | 2.51 | – | – |
| 4-trans-IVc | 5.26 | 3.24 | 7.15 | 4.99 | – | 0.86 |
aNBO calculations were realized with an energy threshold of 0.5 kcal mol−1.