Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 8--monocycloalkanes

Carbon-carbon and carbon-hydrogen spin-spin coupling constants were calculated in the series of the first six monocycloalkanes using SOPPA and SOPPA(CCSD) methods, and very good agreement with the available experimental data was achieved, with the latter method showing slightly better results in most cases, at least in those involving calculations of J(C,C). Benchmark calculations of all possible 21 coupling constants J(C,C), J(C,H) and J(H,H) in chair cyclohexane revealed the importance of using the appropriate level of theory and adequate quality of the basis sets. Many unknown couplings in this series were predicted with high confidence and several interesting structural trends (hybridization effects, multipath coupling transmission mechanisms, hyperconjugative interactions) were elucidated and are discussed based on the present calculations of spin-spin couplings.     

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 7--spiroalkanes

Carbon-carbon spin-spin coupling constants were calculated at the SOPPA level for a series of seven classical spiroalkanes, spiro[2.2]pentane, spiro[2.3]hexane, spiro[2.4]heptane, spiro[2.5]octane, spiro[3.3]heptane, spiro[4.4]nonane and spiro[5.5]undecane, with special focus upon couplings involving and/or across spiro carbons. Many interesting structural trends were investigated originating in specific geometries and unusual bonding environments at the spiro carbon.     

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 10--carbocages

A comprehensive theoretical study of nine classical caged polycycloalkanes (tetrahedrane, prismane, homoprismane, quadricyclane, cubane, pentaprismane, hexaprismane, adamantane and diamantane) was carried out with special focus on the structural behavior of their J(C,C) values calculated at the SOPPA level. The structural behavior of J(C,C) in small carbocages is dominated by steric strain whereas in medium-sized polycycloalkanes the J(C,C) values show no marked peculiarities and follow several well-defined structural trends typical of other alicyclic compounds.     

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 6: propellanes

A full set of carbon-carbon coupling constants have been calculated at the SOPPA level in the series of six most representative propellanes. Special attention was focused on spin-spin couplings involving both bridgehead carbons, and these data were rationalized in terms of the multipath coupling mechanism and hybridization effects. Many unknown couplings in the propellane frameworks were predicted with high reliability.     

Non-empirical calculations of NMR indirect spin-spin coupling constants. Part 13: configurational assignment of aminosulfonylamidines

Carbon-carbon coupling constants have been experimentally measured using the INADEQUATE pulse sequence in the series of N-[1,2-bis(dialkylamino)-2-arylethylidene]arylsulfonamides obtained from N-(1-aryl-2,2,2-trichloroethyl)amides of arylsulfonic acids. Comparison of the experimental J(C,C) in this series with those calculated at the SOPPA (Second-Order Polarization Propagator Approach) level in the model aminosulfonylamidine provided an unambiguous assignment at the C=N bond of the eight-title aminosulfonylamidines to E-configuration, while the unknown J(C,C) couplings in their inaccessible diverse Z isomers have been predicted with high reliability. The established marked difference between J(C,C) of the corresponding carbon-carbon bonds in cis and trans orientations to the nitrogen lone pair in aminosulfonylamidines provides a powerful tool in the configurational assignment at the C=N bond in a wide series of the related systems containing the C=N-SO2R moiety.     

Non-empirical calculations of NMR indirect carbon-carbon coupling constants. Part 11--saturated carbocycles: a reference data set and a practical guide to structural elucidation

Carbon-carbon spin-spin coupling constants, J(C,C), calculated at the SOPPA level for 50 mono-, bi- and polycycloalkanes in 10 previous papers are put in order and discussed on unified grounds. Basic structural trends of J(C,C) established in the original publications are summarized and briefly outlined for the representative series. Many unknown couplings are predicted with high reliability, and this provides a good reference data set and a practical guide to the structural elucidation of saturated carbocycles by means of J(C,C) coupling constants.     

Nonempirical calculations of NMR indirect spin-spin coupling constants. Part 15: pyrrolylpyridines

Conformational study of 2-(2-pyrrolyl)pyridine and 2,6-di(2-pyrrolyl)pyridine was performed on the basis of the experimental measurements and high-level ab initio calculations of the one-bond 13C-13C, 13C-1H and 15N-1H spin-spin coupling constants showing marked stereochemical behavior upon the internal rotation around the pyrrole-pyridine interheterocyclic bonds. Both compounds were established to adopt predominant s-cis conformations with no noticeable out-of-plane deviations.     

Nonempirical calculations of NMR indirect spin-spin coupling constants. Part 14: azomethines of the alpha, beta-unsaturated aldehydes

Configurational assignment of seven azomethines obtained from the alpha-functionally substituted and nonsubstituted alpha,beta-unsaturated aldehydes has been performed on the basis of experimental measurements and the high-level ab initio calculations of their 1J(C,C) and 1J(C,H), involving the alpha-imino carbon that demonstrated the marked stereochemical dependence of both coupling constants upon the orientation of the nitrogen lone pair in the diverse isomers of the title azomethines.     

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

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[1.1.1]pentane as a benchmark to investigate the influence of geometry, basis set and electronic correlation. The calculations performed demonstrated that classical ab initio SOPPA applied with the locally dense Dunning's sets augmented with inner core s‐functions used for coupled carbons and Sauer's sets augmented with tight s‐functions used for coupled hydrogens performs perfectly well in reproducing experimental values of different types of coupling constants (the estimated reliability is ca 1–2 Hz) in relatively large organic molecules of up to 11 carbon atoms. Additive coupling increments were derived for J(C,C), J(C,H) and J(H,H) based on the calculated values of coupling constants within SOPPA in the model bicycloalkanes, in reasonably good agreement with the known values obtained earlier on pure empirical grounds. Most of the bridgehead couplings in all but one bicycloalkane appeared to be essentially additive within ca 2–3 Hz while bicyclo[1.1.1]pentane demonstrated dramatic non‐additivity of ?14.5 Hz for J(C,C), +16.6 Hz for J(H,H) and ?5.5 Hz for J(C,H), in line with previous findings. Non‐additivity effects in the latter compound established at the SOPPA level should be attributed to the through‐space non‐bonded interactions at bridgeheads due to the essential overlapping of the bridgehead rear lobes which provides an additional and effective non‐bonding coupling path for the bridgehead carbons and their protons in the bicyclopentane framework. Copyright © 2003 John Wiley & Sons, Ltd.     

Non‐empirical calculations of NMR indirect carbon‐carbon coupling constants. Part 5: Bridged bicycloalkanes

All possible J(C,C) of the bicarbocyclic frameworks together with J(C,H) and J(H,H) at bridgeheads in the series of six bridged bicycloalkanes, bicyclo[1.1.0]butane, bicyclo[2.1.0]pentane, bicyclo[3.1.0]hexane, bicyclo[2.2.0]hexane, bicyclo[3.2.0]heptane and bicyclo[3.3.0]octane, were calculated at the SOPPA level with correlation consistent Dunning sets cc‐pVTZ‐Cs augmented with inner core s‐functions and locally dense Sauer sets aug‐cc‐pVTZ‐J augmented with tight s‐functions and rationalized in terms of the multipath coupling mechanism and hybridization effects explaining many interesting structural trends. Copyright © 2003 John Wiley & Sons, Ltd.     

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. Copyright © 2003 John Wiley & Sons, Ltd.     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 2. Strained polycarbocycles

High‐level non‐empirical calculations of carbon–carbon spin–spin coupling constants in a series of strained polycarbocycles have been carried out, in excellent agreement with available experimental data. The utmost importance of electronic correlation effects in this case has been demonstrated and it has been shown that the Second‐Order Polarization Propagator Approach (SOPPA) is an adequate method to account for those effects. It has been demonstrated that the most reliable basis sets to calculate J(C,C) at the SOPPA level are the correlation‐consistent basis sets of Dunning and co‐workers augmented with inner core s‐functions or decontracted in their s‐parts. The nature of the unusual bridgehead–bridgehead bonds in bicyclobutane and propellane in terms of s‐characters of bonding hybrids and also the hybridization effects in spiropentane are discussed based on the arguments derived from the current calculations of J(C,C) in the title compounds. The values of the unknown J(C,C) in propellane and spiropentane are predicted with high reliability. Copyright © 2003 John Wiley & Sons, Ltd.     

Non-empirical interpretation of nitrogen 14 nuclear quadrupole coupling constants

The ¹⁴N nuclear quadrupolar coupling constants have been calculated for a series of nitrogen containing molecules from ab initio SCF-LCAO-MO wavefunctions built on basis sets of Gaussian type atomic functions. The various nuclear and electronic (from MO's, atoms, basis functions) contributions to the total field gradient have been analyzed and their relation to molecular and electronic structure is discussed.The effect of the nature of the basis set on the accuracy of the computed field gradients has also been studied.

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Zusammenfassung Die ¹⁴N-Kernquadrupol-Kopplungskonstanten sind für eine Reihe von N-haltigen Verbindungen aus ab initio-Wellenfunktionen, die auf Gauß-Orbitalen basieren, berechnet worden. Die einzelnen Kern- und Elektronenbeiträge zum Feldgradienten wurden untersucht und diskutiert, desgleichen der Einfluß des Typus der Basis auf die Genauigkeit der Resultate.

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Résumé Les constantes de couplage quadrupolaire nucléaire de ¹⁴N ont été calculées pour une série de composés azotés à partir de fonctions d'onde ab initio SCF-LCAO-MO (Hartree-Fock) construites sur une base de fonctions atomiques gaussiennes. Les diverses contributions nucléaires et électroniques (provenant des orbitales moléculaires, des atomes, des fonctions atomique de base) au gradient de champ total ont été analysées et reliées aux caractéristiques structurales des molécules considérées.L'effet de la nature de la base de fonctions atomiques sur la précision des gradients de champs calculés a aussi été étudié.

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We thank Drs. H. Basch, J. L. Calais, J. F. Harrison and P. Pyykkö for sending us test calculations for checking our program and Drs. H. Basch and G. Berthier for communicating to us the molecular wavefunctions of some of the nitrogen containing heterocycles.     

The stereochemical dependence of one-bond carbon-carbon coupling constants

Spin-spin coupling constants for carbon-carbon single bonds vary with the orientation of lone pairs on adjacent nitrogen atoms and of adjacent carbonyl groups.     

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 1. Three‐membered rings

The carbon–carbon indirect nuclear spin–spin coupling constants in cyclopropane, aziridine and oxirane were investigated by means of ab initio calculations at the RPA, SOPPA and DFT/B3LYP levels. We found that the carbon–carbon couplings are by far dominated by the Fermi contact term. Our best SOPPA and DFT results are in a very good agreement with each other and with the experimental values, whereas calculations at the RPA level of theory strongly overestimate the carbon–carbon couplings. Significant differences in the basis set dependence of the calculated carbon–carbon coupling constants obtained with either wavefunction method, RPA or SOPPA, or the density functional method, DFT/B3LYP, are observed. The SOPPA results depend much more strongly on the quality of the basis set than the results of DFT/B3LYP calculations. The medium‐sized core‐valence basis sets cc‐pCVTZ and even cc‐pCVDZ were found to perform fairly well at the SOPPA level for the one‐bond carbon–carbon couplings investigated here. Copyright © 2002 John Wiley & Sons, Ltd.     

Non-empirical calculations of chlorine quadrupole coupling parameters in chloromethanes and chlorosilanes

Non-empirical calculations of the field gradient tensor at the chlorine nucleus are resorted for chloromethane, trichloromethane, chlorosilane and trichlorosilane. The calculations agree quite well with the experimental quadrupole coupling constants. The calculated asymmetry parameters in trichloromethane and trichlorosilane are low and the principal z axis of the field gradient tensor is found nearly to coincide with the CCl and SiCl bond directions.     

NDDO MO calculations: isotropic hyperfine coupling constants and nuclear spin-spin coupling constants

The nonempirical NDDO MO method in its unrestricted form has been used to evaluate isotropic hyperfine coupling constants and nuclear spin-spin coupling constants. Satisfactory agreement with INDO and experimental results is obtained.     

Interaction energies and NMR indirect nuclear spin-spin coupling constants in linear HCN and HNC complexes

The cooperativity effects on both the electronic energy and NMR indirect nuclear spin-spin coupling constants J of the linear complexes (HCN)n and (HNC)n (n = 1-6) are discussed. The geometries of the complexes were optimized at the MP2 level by using the cc-pVTZ basis sets. The spin-spin coupling constants were calculated at the level of the second-order polarization propagator approximation with use of the local dense basis set scheme based on the cc-pVTZ-J basis sets. We find strong correlations in the patterns of different properties such as interaction energy, hydrogen bond distances, and spin-spin coupling constants for both series of compounds. The intramolecular spin-spin couplings are with two exceptions dominated by the Fermi contact (FC) mechanism, while the FC term is the only nonvanishing contribution for the intermolecular couplings. The latter do not follow the Dirac vector model and are important only between nearest neighbors.     

Coupled hartree-fock and second order polarization propagator calculations of indirect nuclear spin-spin coupling constants for diatomic molecules

We report ab initio calculation of indirect nuclear spin-spin coupling constants for the HD, FH, CO and CH⁺ molecules using the first (coupled Hart