Absolute Conformation Revisited: Experimental Approach

We propose that the term “absolute conformation” be used when one of the chiroptical properties is correlated with one of a pair of enantiomeric conformations. We present examples of compounds for which absolute conformations are known, as well as their syntheses, enantiomer resolution, and determination of absolute conformations, and discuss specifications of those conformations. The examples were selected from molecules for which one conformation is optically inactive but, by internal rotation about a C(sp3)−C(sp3) bond, optically active conformers are produced. There are some problems, which we discuss as Future Problems, that arise when conformations are taken into account, even though the classical treatment of stereochemistry is well established in such areas. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)