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Helical twisting power and chirality indices

We review the statistical theory of helical twisting power and propose an alternative derivation of the results obtained by Nordio and co-workers [1999, J. chem. Soc. Perkin Trans., 2, 411]. We examine chiral indices which include an interaction between the host and dopant, then compare these with chiral indices dependent only on the dopant structure. We discuss the need for the inclusion of the interaction between dopant and host in the description of chiral induction, and discuss alternative measures of chirality and their shortcomings. We show that both the previously suggested surface indices and the newly proposed one vanish for at least one class of non-trivial chiral structures. We compare the results obtained from these surface indices with a more general 3D chiral index and evaluate these indices for four helicene (M)-1–4 molecules.