ACCURATE DETERMINATION AND ANALYSIS OF THE TEMPERATURE-DEPENDENCE OF LONG-RANGE SPIN-SPIN COUPLINGS IN 2-CHLOROBENZALDEHYDE

The proton‐proton spin‐spin couplings of 2‐chlorobenzaldehyde were determined accurately for acetone‐d6 and CD3CN solutions at several temperatures. The sign and temperature dependence of the para‐benzylic six‐bond coupling, 6Jα4, was also obtained, although the observed value of this indicator of the formyl–ring co‐planarity was in the range −24 to −31 mHz. The fitting of the temperature dependence suggests that 6J0 (the value of the coupling when the formyl‐ring dihedral angle is 0°) is very small and probably positive, in contrast, for example, to styrene. The results are discussed on the basis of some modified INDO/FP calculations. A simple resolution enhancement technique is also described. Copyright © 1990 John Wiley & Sons, Ltd.