Chiroptical spectra and molecular geometry of bicyclic dithioimides
摘要:
Several chiral bicyclic dithioimides were prepared by thionation of the parent imides with Lawesson's reagent. Due to a flexibility of the dithioimide chromophore, their CD spectra show significant solvent dependence. A substantial deviation of the chromophore from planarity was confirmed by the MNDO calculations and crystallographic structures of 4, 5b, 6 and 7. The observed CE sign corresponding to the lowest energy n-pi* transition can be predicted, upon careful examination of the molecular geometry, by the antioctant rule with sector signs opposite to those known for ketones. (C) 1998 Elsevier Science Ltd. All rights reserved.
Molecular geometry and circular dichroism spectra of bicyclo[2.2.1]heptane-2,3-dicarboxylic anhydrides and imides
摘要:
Several tricyclic anhydrides and imides derived from optically active bicyclo[2.2.1]heptane-2,3-dicarboxylic acids were synthesized, and their circular dichroism spectra are reported. On the basis of MNDO calculations it was estalished that despite rigidity of the norbornane system the five-membered rings of succinic anhydride and imide moieties are slightly twisted. The chromophores are flexible and can be more or less skewed depending on solvent polarity. The chromophore nonplanarity significantly influences magnitude and sign of the first Cotton effect associated with the lowest energy n-pi* electronic transition. The sign of the second n-pi* Cotton effect is governed by vicinal effect of substituents. The crystal structures of three N-(S)-1-phenylethylimides were solved to establish the configuration at C-2 of the imide moieties.
Conformational dependence of the circular dichroism of N-nitrosopyrrolidines
作者:Tadeusz Polonski、Maria J. Milewska、Andrzej Katrusiak
DOI:10.1021/ja00077a045
日期:1993.12
suhstituted N-nitrosopyrrolidines were prepared and their chiroptical spectra studied. The circulardichroism of monocyclic compounds depends on substituents, solvents, and temperature changes. Some of these N-nitrosamines exhibit bisignate CD curves in the region of n-π * transition. On the contrary, conformationally restrictcd bi- and tricyclic compounds show monosignate Cotton effects, the magnitudes
制备了几种取代的 N-亚硝基吡咯烷并研究了它们的手性光谱。单环化合物的圆二色性取决于取代基、溶剂和温度变化。这些 N-亚硝胺中的一些在 n-π * 跃迁区域表现出双信号 CD 曲线。相反,构象受限的双环和三环化合物表现出单信号棉花效应,其大小几乎与溶剂无关。双标志 CD 曲线是由处于平衡状态的吡咯烷环的两个半椅构象异构体产生的,并有助于相反的 CD 符号。棉花效应迹象可以通过我们之前制定的“降低对称性”扇区规则来预测
Chiroptical spectra and molecular geometry of bicyclic dithioimides
作者:Maria J. Milewska、Maria Gdaniec、Hanna Małuszyńska、Tadeusz Połoński
DOI:10.1016/s0957-4166(98)00293-6
日期:1998.9
Several chiral bicyclic dithioimides were prepared by thionation of the parent imides with Lawesson's reagent. Due to a flexibility of the dithioimide chromophore, their CD spectra show significant solvent dependence. A substantial deviation of the chromophore from planarity was confirmed by the MNDO calculations and crystallographic structures of 4, 5b, 6 and 7. The observed CE sign corresponding to the lowest energy n-pi* transition can be predicted, upon careful examination of the molecular geometry, by the antioctant rule with sector signs opposite to those known for ketones. (C) 1998 Elsevier Science Ltd. All rights reserved.
Molecular geometry and circular dichroism spectra of bicyclo[2.2.1]heptane-2,3-dicarboxylic anhydrides and imides
作者:Tadeusz Polonski、Maria J. Milewska、Maria Gdaniec、Miroslaw Gilski
DOI:10.1021/jo00063a038
日期:1993.5
Several tricyclic anhydrides and imides derived from optically active bicyclo[2.2.1]heptane-2,3-dicarboxylic acids were synthesized, and their circular dichroism spectra are reported. On the basis of MNDO calculations it was estalished that despite rigidity of the norbornane system the five-membered rings of succinic anhydride and imide moieties are slightly twisted. The chromophores are flexible and can be more or less skewed depending on solvent polarity. The chromophore nonplanarity significantly influences magnitude and sign of the first Cotton effect associated with the lowest energy n-pi* electronic transition. The sign of the second n-pi* Cotton effect is governed by vicinal effect of substituents. The crystal structures of three N-(S)-1-phenylethylimides were solved to establish the configuration at C-2 of the imide moieties.