3J(HH)Pμ,ν correlation for planar 7‐membered cyclic π‐systems—structural effects on 3J(HH)

It is shown that sterically unperturbed vicinal HH coupling constants in planar 7‐membered π‐systems correlate linearly with the HMO π‐bond order: 3J(HH) = 20.91Pμ,ν–3.85 (r.m.s. error 0.26 Hz, correlation coefficient =0.988). Systematic deviations from this relationship which most probably originate from valence angle changes are found for fused π‐systems containing rings of different size. Model calculations using the CNDO/2 method as well as finite perturbation theory and INDO wave functions support the experimental findings. An improvement of existing 3J(HH)Pμ,ν correlations for planar 6‐membered rings is possible if CNDO/2 π‐bond orders are used instead of HMO or PPP‐SCF data.