Table 1.
X-ray crystallographic structural parameters and NBO data for compounds 1–8
| Compounds | Y | X | d1 | d2 | θ 1 | θ 2 | ∆1 | ∆2 | Θ1 | Θ2 | n→π* (kcal mol−1) | Total n→π* (kcal mol−1) | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| (Å) | (Å) | (°) | (°) | (Å) | (Å) | (°) | (°) | E 1 (n→π*) | E 2 (n→π*) | E t (n→π*) | |||
| 1 | H | CH3 | 3.487 | 3.542 | 98.7 | 95.9 | 0.018 | 0.007 | 2.39 | 0.99 | NP | NP | NP |
| 2 | H | CH2CH3 | 3.314 | 3.331 | 93.7 | 93.2 | 0.013 | 0.026 | 1.70 | 3.43 | 0.03 | 0.03 | 0.06 |
| 3 | CH3 | CH3 | 3.367 | 3.365 | 92.8 | 92.7 | 0.008 | 0.015 | 0.99 | 1.89 | 0.01 | 0.02 | 0.03 |
| 4 | CH3 | CH2Cl | 3.103 | 3.037 | 82.8 | 85.6 | −0.015 | 0.000 | −1.96 | 0.012 | 0.10 | 0.34 | 0.44 |
| 5 | OCH3 | CH3 | 3.233 | 3.152 | 81.8 | 85.4 | 0.005 | −0.005 | 0.63 | −0.69 | 0.03 | 0.16 | 0.19 |
| 6 | OCH3 | CH2Cl | 3.072 | 3.009 | 82.1 | 84.9 | −0.005 | −0.019 | −0.70 | −2.59 | 0.14 | 0.42 | 0.56 |
| 7 | Br | CH2Cl | 3.123 | 3.014 | 81.3 | 86.2 | −0.019 | −0.009 | −2.53 | −1.17 | 0.08 | 0.39 | 0.47 |
| 8 | OCH3 | CH2Br | 3.082 | 3.017 | 81.9 | 84.8 | −0.014 | −0.017 | −1.92 | −2.34 | 0.14 | 0.40 | 0.54 |
The calculations were carried out at B3LYP/6-311 + G(2d,p) level of theory. d1 = O1···C2; d2 = O2···C1; θ 1 = ∠O1···C2 = O2; θ 2 = ∠O2···C1 = O1 (see Fig. 2b). E 1 (n→π*) is the NBO second order perturbation energy for electron donation from oxygen lone pair (n O) of the first carbonyl group (CO-I) to the π*C=O orbital of the second carbonyl group (CO-II). E 2 (n→π*) is the NBO second order perturbation energy for electron donation from oxygen lone pair (n O) of the second carbonyl group (CO-II) to the π*C=O orbital of the first carbonyl group (CO-I). E t (n→π*) = E 1 (n→π*) + E 2 (n→π*)
NP not present