Circular dichroism and absolute conformation of Δ4-uronate derivatives: a semi-empirical rule for inherent chiral α-alkoxy acrylates (original) (raw)

1998, Chemical Communications

By Giinther S n a t z k e [ * l Although chiroptical methods have been used in chemistry for some 150 years, and the basic theory was developed by Rosenfeld 50 years ago, their success in determining absolute conformation rests mainly on empirical rules. Some of these can be proved theoretically ; however, in the case of more complex molecules this is not yet always possible. In what follows, an attempt is made to bridge the wide gap between theory and empiricism: "qualitative MO-theory", which has already been successfully used to explain reaction mechanisms, the shape of molecules, or photoelectron spectra, can also be applied to circular dichroism (CD). In general we shall have to be content with a reasonable interpretation of the experimentally determined sign correlation, but even this will be of great value since it can yield general relations between the geometry of molecules and the sign of CD. Such relations become particularly important when only a few examples of a given chromophore are known. If first and second sphere of a molecule are achiral then sector rules can be put forward, and in other cases helicity or chirality rules. 1. Chiroptical Phenomena Circular dichroism (CD) is nowadays the most frequently used chiroptical method [others involve e. g. measurement of optical rotation or optical rotatory dispersion, ellipticity, Raman-CID ("Raman Circular Intensity Differential"), CD p] Prof. Dr. G. Snatzke Lehrstuhl f i r Strukturchemie der Universitat Postfach 102148, D-4630 Bochum 1 (Germany)