Application of Electronic Circular Dichroism in Configurational and Conformational Analysis of Organic Compounds

Abstract

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Salvianolic acids T and U: A pair of atropisomeric trimeric caffeic acids derivatives from root of Salvia miltiorrhiza

“…So we turn to the conformation search for help [10]. The dihedral angle scanning result indicated that two conformations existed ( Table 2, Fig.…”

Electronic Circular Dichroism

“…The consequence of this interaction is the formation of two different normal oscillation modes (in-phase and out of phase) with different frequencies (leading to a more or less pronounced splitting or broadening of the absorption band) and opposite rotational strengths. For reviews of the so-called exciton chirality rule, depicted in Figure 9.1, see Refs [2,3,11].…”

“…A clockwise twist to bring the chromophore (actually its electric dipole transition moment) in the front onto that in the back is defined as positive chirality, and corresponds to a positive couplet in the ECD spectrum. This consists in a bisignate feature with positive long-wavelength branch [2,3,11].…”

“…Moreover, the fact that optical activity is essentially centered on chromophores gives chemists the opportunity to change ECD by modifying the chromophores, that is, by inserting groups that extend conjugation or by adding new chromophores [2,3].…”

“…Put on a ground familiar to ECD users, these relationships correspond to the so-called helicity or sector rules. They relate the sign of a specific ECD band to the inherent chirality of the chromophore responsible for it (helicity rules like the diene one) or to the spatial disposition of a certain perturber with respect to an achiral chromophore responsible for it (sector rules like the ketone octant rule) [2,71,72]. These rules have represented in the past popular means of interpreting ECD spectra and especially of assigning ACs, but nowadays their use is greatly downsized.…”