Conformational equilibria of citral

The conformational behavior of citral was examined by NMR spectroscopy and DFT calculations wherein s-trans conformations were found to dominate over s-cis conformations based on temperature-dependent vicinal and through-space couplings and the calculations. The amount of s-cis conformation present, however, is non-negligible. The coupling constants were also calculated with a good correlation with the experiments, with an exception that too low a value for vicinal coupling of the s-trans conformer of the conjugated CH-CHO system was predicted. According to DFT, the most stable structure is an E-s-trans conformer which is 2.0 kJ mol−1 more stable than the most stable Z-s-trans conformer, i.e. E-citral is slightly more stable than Z-citral.