Stereochemical study of iminodihydrofurans based on experimental measurements and SOPPA calculations of (13)C-(13)C spin-spin coupling constants

Configurational assignment and conformational analysis of a series of iminodihydrofurans obtained from cyanoacetylenic alcohols were performed on the basis of experimental measurements and high-level ab initio calculations of their (13)C-(13)C spin-spin coupling constants. The title compounds were shown to form and exist in solution as the individual Z isomers, adopting the orthogonal orientation of the amino, alkylamino and dialkylamino groups and the s-trans orientation of the CONH(2) group at the C(4) position of the 2,5-dihydro-2-iminofuran moiety.     

Interbenzylic 19F,19F spin-spin coupling constants in bis(fluoromethyl) arenes

Five- to eleven-bond F,F spin coupling is observed in bis(fluoromethyl)arenes. According to INDO MO calculations, these couplings are transmitted mainly via the aromatic π-system. The low preference of 1,4-(CH₂F)₂-benzene for the conformation in which the C? F bonds are perpendicular to the aromatic ring is shown by the strong increase of⁷J(FF) upon double ortho-substitution.     

An experimental and theoretical study of spin-spin coupling in chlorosilanes

An experimental and theoretical study of the absolute value of the one-bond spin-spin coupling constant |(1)J(Si,H)| in SiH(n)Cl(4-n) (n = 0-4) dissolved in THF-d(8) is presented. We found |(1)J(Si,H)| to increase with an increasing number of chlorine substituents, and the quantitative changes were found to differ from the values previously reported for the same compounds dissolved in cyclohexane-d(12). We also report on the variations in |(1)J(Si,H)| as a function of temperature, which we found to be linearly temperature dependent for the chlorine-substituted silanes and temperature independent for SiH(4). Furthermore, the temperature dependence of |(1)J(Si,H)| varied between the different chlorosilanes. Solvent-solute interactions were studied by quantum chemical DFT calculations. The variations in chloro-silane bond lengths upon adduct formation and the different adduct interaction energies may explain the temperature dependences of the coupling constants.     

13C-13C spin-spin coupling constants in the spectra of monosubstituted pyridines

The ¹³C- {¹H} NMR spectra of pyridine and a number of monosubstituted pyridines for compounds with the natural percentage of the ¹³C isotope were analyzed. The direct, geminal, and vicinal ¹³C-¹³C spin-spin coupling constants (SSCC) were determined. Linear relationships that link the ¹³C-¹³C SSCC in the spectra of monosubstituted pyridines and benzenes were obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1383–1385, October, 1985.     

Direct 13C-13C spin-spin coupling constants in the vinyl group of N-vinylazoles

The unshared electron pair of the dicoordinated nitrogen atom introduces a stereospecific contribution to the ¹³C-¹³C spin-spin coupling constant (SSCC) in the vinyl group of a series of N-vinylazoles, the value of which depends on the energetics of the unshared pair.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 197–200, February, 1989.     

Direct13C-13C spin-spin coupling constants of olefinic carbons in vinyl ethers

Conclusions In alkyl vinyl ethers, the values of¹J (¹³C=¹³C) SSCC increase with increasing effective volume of the alkyl group, opposite to the change in the corresponding constants in the series of alkyl phenyl ethers.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2249–2252, October, 1982.     

19F-19F spin-spin coupling constant surfaces for (HF)2 clusters: the orientation and distance dependence of the sign and magnitude of J(F-F)

Ab initio calculations using the equation-of-motion coupled cluster method have been carried out to investigate 19F-19F spin-spin coupling constants for a pair of HF molecules. The overall features of the J(F-F) coupling surface with respect to the F-F distance and the orientation of the pair of HF molecules reflect those of the Fermi-contact (FC) surface, although the FC term may not be a good quantitative estimate of J(F-F). The hydrogen-bonded HF dimer exhibits unusual behavior compared to other hydrogen-bonded complexes, since both the FC term and 2hJ(F-F) exhibit variations in sign and magnitude as the F-F distance changes and the linearity of the hydrogen bond is destroyed. The FC term for F-F coupling is relative small and negative for the equilibrium dimer. At the dimer F-F distance, the maximum negative value for the FC term is found for the linear arrangement F-H...H-F, while the maximum positive value is found for the linear H-F...F-H arrangement, despite the fact that neither of these structures is bound. Changes in the sign and magnitude of the FC term are analyzed using the nuclear magnetic resonance triplet wave function model, which relates the orientation of magnetic nuclei to the phases of the wave functions for excited triplet states that couple to the ground state. The FC term for a particular orientation is a result of competing positive and negative contributions from different triplet states, the sign of each contribution being determined by the alignment of the nuclear magnetic moments in that state. Factors are identified which must play a role in determining which types of wave functions dominate.     

NMR study of conjugation effects 15.13C-13C spin-spin coupling constants in phenyl alkyl ether

Conclusions ¹³C-¹³C SSCC were measured for a series of phenyl alkyl ethers. The values through the bond between C² and C³ in mono substituted benzenes most clearly reflect the -electron interaction of the aromatic ring with the substituent, provided the latter contains no atoms from a period of the periodic table higher than the second.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya.No. 1, pp. 113–119, January, 1982.The authors thank N. M. Sergeev for useful discussions while the work was in progress, and V. N. Khlopkov for technical assistance in setting up the experiments.     

13C-labeled platinum(IV)-carbohydrate complexes: structure determination based on (1)H-(1)H, (13)C-(1)H, and (13)C-(13)C spin-spin coupling constants

The reaction of D-mannose and D-allose with [PtMe(3)(Me(2)CO)(3)]BF(4) 1 in acetone affords complexes [PtMe(3)L]BF(4) 5 and 6 (5, L = alpha-D-mannofuranose; 6, L = beta-D-allofuranose). The coordination mode and conformation of the carbohydrate ligands in 5 and 6 in acetone-d(6) have been determined from an analysis of J(HH), J(CH), and J(CC) in complexes formed using site-specific (13)C-labeled D-mannose and D-allose. These coupling data are compared to those measured in (13)C-labeled complex [PtMe(3)L]BF(4) 2 (L = 1, 2-O-isopropylidene-alpha-D-glucofuranose) and 1, 2-O-isopropylidene-alpha-D-glucofuranose 3, whose solid-state structures are known, and in (13)C-labeled 1,2;5, 6-di-O-isopropylidene-alpha-D-glucofuranose 4. The preferred furanose ring conformations in 2 and 5 are very similar ((3)E/E(4) and E(4)/(o)E/E(1), respectively; eastern hemisphere of the pseudorotational itinerary), with platinum coordination involving O3, O5, and O6 of the saccharide. In contrast, the furanose ring of 6 prefers an (4)E/E(o)/(1)E geometry (western hemisphere of the pseudorotational itinerary) resulting from altered complexation involving O1, O5, and O6. Couplings within the exocyclic fragments of 2, 5, and 6 also support the existence of two different platinum coordination modes. In addition to establishing the structures and conformations of 2, 5, and 6 in solution, one-, two-, and three-bond J(CH) and J(CC) observed in these complexes provide new insights into the effect of structure and conformation on the magnitudes of these couplings in saccharides. Weak platinum(IV) complexation with the carbohydrate conformationally restricts the furanose and exocyclic fragment without introducing undesirable structural strain, thereby allowing more reliable correlations between structure and coupling magnitude.     

13C-13C spin-spin coupling constants in structural studies: XLIII. Stereochemical study on functionalized 3-iminopyrrolizines

Three 1-ethylsulfanyl-3-imino-3H-pyrrolizine-2-carboxamides were synthesized by intramolecular cyclization of substituted (2Z)-2-cyano-3-ethylsulfanyl-3-(1H-pyrrol-2-yl)prop-2-enamides. The products were assigned syn configuration at the C=N bond and preferential s-cis orientation of the carbamoyl group on the basis of the experimental ¹³C-¹³C coupling constants and high-level nonempirical quantum-chemical calculations.     

13C-15N spin-spin coupling constants of amides: H-bonding effects in a cyclohexapeptide

The effect of intramolecular H-bonding and solvent acidity on the magnitude of one-bond ¹³C-¹⁵N spin-spin coupling constants has been examined using specifically ¹⁵N-labeled $\text{cyclo}$-(Gly-L-Pro-Gly)₂ and related linear peptides.     

Additivity of long-range spin-spin coupling constants J(13C-H) in substituted benzenes

Theoretical and Experimental Chemistry -     

Steric specificity of the direct13C-1H spin-spin coupling constants in the vinyl group in N-vinylpyrroles

Conclusions The direct¹³C-¹H spin-spin coupling constants of the vinyl group -carbon in N-vinyl-pyrroles display steric specificity and change depending on the dihedral angle between the planes of the vinyl group and the heterocycle.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1418–1421, June, 1987.     

Additivity of 13C-1H and 1H-1H spin-spin coupling constants in six-membered aromatic nitrogen-containing heterocycles

We have analyzed proton-coupled ¹³C NMR and PMR spectra of pyridazine, pyrimidine, pyrazine, 1,3,5-triazine, and 1,2,4-triazine for one-molar solutions of the compounds in DMSO-D₆. Comparison of the values obtained for the ¹³C-¹H and ¹H-¹H spin-spin coupling constants with the values calculated on the basis of the spin-spin coupling constants in pyridine and benzene has shown that it is possible to predict the constants using linear additive equations. Substantial nonlinear deviations (5–6 Hz) are observed for ¹J_CH when the carbon atom is located between two adjacent nitrogen atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 986–990, July, 1985.