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.
Chiroptical properties of 1,2-cyclopropanedicarboxylic anhydrides and imides. The cyclopropane ring contribution to the Cotton effect
摘要:
Several optically active 1,2-cyclopropanedicarboxylic anhydrides and imides were prepared and their chiroptical spectra studied. Despite the strained bicyclic skeleton of these compounds, their CD spectra show an unusual solvent dependence. This phenomenon can be explained in terms of the cyclopropane ring contribution to the Cotton effect. A deviation of the skeleton and the anhydride or imide group from the local C(s) symmetry, shown by MNDO calculations, causes formation of an inherently chiral chromophore constituted by the three-membered ring and neighboring carbonyls. This kind of chromophore is responsible for the observed strong Cotton effects.