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‐ d 6 and CD 3 CN solutions at several temperatures. The sign and temperature dependence of the para ‐benzylic six‐bond coupling, 6 J α4 , 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 6 J 0 (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.