Carbon‐13, ¹H spin‐spin coupling. V—π‐benzenechromium tricarbonyl and the π‐tropyliumchromium tricarbonyl cation

The 13 C, 1 H spin‐spin coupling constants have been determined for π‐benzenechromium tricarbonyl (3) and the π‐tropyliumchromium tricarbonyl cation using the 13 C{ 2 H}double resonance technique described in a previous paper. In addition, conventional analysis of the 1 H‐coupled 13 C NMR spectrum of 3 was carried out and the 1 H NMR spectrum of 3 partially oriented in the nematic phase was analysed. Both treatments also allowed the determination of the 1 H, 1 H coupling constants for this compound. The n J (CH) results are discussed on the basis of structural data and the theoretical results available. The complexation effects for 1 J (CH) are found to correlate with the CH overlap population and hybridization changes, and those for 3 J (CH) with the CC bond lengths and π‐bond orders. The dependence of 2 J (CH) on CC bond length as well as on the CCH bond angle is indicated. The liquid crystal results are compared with those of related studies.