Semiempirical Rules in Circular Dichroism of Natural Products

Abstract

Qualitative MO-theory is applied to derive at nonempirical rules for the correlation of the sign of a Cotton effect with the stereochemistry of a molecule. For inherently chiral chromopho-res (examples: enol ethers, vinyl cyclopropanes) their absolute conformation gives this sign directly, for inherently (locally) achiral ones perturbation theory has to be used (examples: lactone acids from lichens, hemithioacetals of steroids). A generalization of sector rules is proposed. © IUPAC