Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 4: Bicycloalkanes

Abstract

A systematic study of the one-bond and long-range J(C,C), J(C,H) and J(H,H) in the series of nine bicycloalkanes was performed at the SOPPA level with special emphasis on the coupling transmission mechanisms at bridgeheads. Many unknown couplings were predicted with high reliability. Further refinement of SOPPA computational scheme adjusted for better performance was carried out using bicyclo[1.

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 8—Monocycloalkanes

“…Furthermore, in one of the previous papers 4 in this series, it was unambiguously demonstrated that geometric factors play only a minor role in the calculations of…”

“…The latter may arise from the non-bonded interactions of those carbons such as that involving bridgehead carbons in bicyclo[1.1.1]pentane (separated by ca 1.9Å), as manifested in the series of papers by Barfield and co-workers 107 and later by Contreras and co-workers 108 and well reproduced in our previous SOPPA calculations. 4 Unfortunately, both methods, SOPPA and SOPPA(CCSD), slightly overestimate this interesting coupling, giving ca 10 to 11 Hz compared with the experimental value of ca 8 Hz. 109 Vicinal couplings are ca C2 Hz in cyclohexane (4) and near zero (<0.2 Hz) in larger monocycloalkanes 5 and 6, which is due to the Karplus dependence of 3 J(C,C): the dihedral angles of the coupling paths are ϕ D 54.4°in 4, 85.7°i n 5 and 100.2°in 6, corresponding to a gauche arrangement of the coupled carbons in 4 and a near orthogonal arrangement in 5 and 6.…”

“…Recently, it was demonstrated 4 that SOPPA in combination with locally dense basis sets consisting of Dunning's correlation consistent sets 89 of triple and even double zeta quality augmented with inner core s-functions, 90 cc-pVXZ-Cs (X D D, T), used for coupled carbons, and Sauer's spin-spin coupling sets 33 with tight s-functions, aug-cc-pVTZ-J, used for coupled hydrogens, performs perfectly well in reproducing experimental values of J(C,C), J(C,H) and J(H,H) for carbocyclic compounds. We use here chair cyclohexane optimized at the B3LYP/6-311G ŁŁ level as a benchmark to test the performance of SOPPA and SOPPA(CCSD) when employed with the basis sets described above.…”

“…It is interesting that previously unknown four-bond couplings markedly alternate in sign with 4 information about long-range proton-proton couplings in cyclohexane.…”

“…Seven previous publications in this series devoted to threemembered rings, 1 strained polycycloalkanes, 2 polyhedranes, 3 bicycloalkanes, 4 bridged bicycloalkanes, 5 propellanes 6 and spiroalkanes 7 of up to 14 carbon atoms manifested a real breakthrough of ab initio methods based on the general SOPPA (Second-Order Polarization Propagator Approach) formalism 8,9 to calculate spin-spin coupling constants into the area of organic chemistry. The unprecedented reliability of SOPPA to calculate one-bond and long-range spin-spin coupling constants J(C,C), J(C,H) and J(H,H) in a wide range of carbocyclic compounds has been manifested, however, leaving apart the classical series of monocycloalkanes.…”