Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 3. Polyhedranes

High‐level ab initio calculations of carbon–carbon coupling constants were carried out in tetrahedrane, prismane and cubane using the SOPPA (Second‐Order Polarization Propagator Approach) computational scheme, in good agreement with available experimental data. It was found that SOPPA performs perfectly well in combination with Dunning's correlation‐consistent basis sets augmented with inner core functions; however, no improvement was observed on adding tight s‐functions. The utmost importance of electronic correlation effects decreasing the total values of computed J (C,C) in the title compounds by a factor of ∼2.0–2.5 was found. Unknown values of J (C,C) in the title polyhedranes were predicted with high reliability and the latter were treated in terms of s‐characters of carbon–carbon bonds based on the additive scheme of coupling pathways. All three compounds under study showed decreased s‐characters of their carbon–carbon bonds, which is the result of their remarkable steric strain.