ORGN 591

A helical structure analysis for various types of molecular chirality, including point, axial, planar chiralities and others, is presented. It is shown that, despite of highly diversified structures, all types of chiral molecules¢ optical activities can be attributed to the helical structures that are inherent in them. Molecular chirality is characterized by and equivalent to helicity in every of its geometric and electronic meanings. It is based on this inherent helical structural nature that a generalization of molecular chirality was established. The recognition and identification of helical structure as a universal hallmark of chirality in real molecules is correlated to the classic helix models for optical activity and results a unified and general framework for understanding chirality from both theoretical and experimental perspectives. A structure-function correlation that connects a chiral molecule’s handedness of the net helical structure with its optical rotation sign is revealed: at long wavelengths a chiral molecule with a net right-handed helicity is dextrorotatory, and with a net left-handed helicity is levorotatory. The practical significance of this correlation, i.e., determination of molecular absolute stereochemistry on the basis of rotation data, is illustrated on several bioactive natural products. Two new concepts, geometric helix and physical helix, are proposed to characterize the conformational and electronic properties of molecular chirality respectively. An investigation of the role of physical helix in chiral recognition and asymmetric induction should lead to novel insights of controlling electronic effects in these important processes.