Determination of the stereochemistry of 4-chromenecarbaldehydes using Nuclear Overhauser Enhancements (NOE)

Abstract

The paper reports studies on the use of 4-chromenecarbaldehydes as suitable substrates for the assessment of the accuracy of interpretations of Nuclear Overhauser Enhancements (NOE) data for chromenecarbaldehydes and related compounds, such as the 3,4-dibromochromanones. The investigative protocol that has been used consists of the comparison of NOE data from experiment with those obtained from theoretical considerations based on computational molecular modelling, using PCMODEL. The theoretical conditions that have been considered were two-fold: the chromenecarbaldehydes were considered as either static/planar molecules or as dynamic and puckered structures in which the carbonyl moieties have, at least, torsional vibration. This approach has been found to be a valid one and the dynamic consideration was found to give calculated NOE values close to NOE data obtained from experiment. It is thus believed that a combination of molecular modelling and such computations could be a powerful tool in the elucidation of conformational information from NOE measurements. It has also been shown, from our experiments and theoretical considerations, that in order to avoid an over-simplistic use of NOE data for the detailed assignment of conformational equilibra and diastereoisomerism, one must ensure that enhancements from the same experiments are considered. JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 2 No. 1 (2000) pp. 80-86