13C-13C Spin-spin Coupling Constants Research Articles

13C-13C spin-spin coupling constants in structural studies: XLIV. Carbonyl-containing oximes

13C-13C spin-spin coupling constants in carbonyl-containing oximes were calculated in terms of the second-order polarization propagator approximation (SOPPA) with account taken of the results of theoretical conformational analysis. Stable conformations of all carbonyl-containing oximes were found to have s-trans orientation of the carbonyl group in the E and Z isomers. The corresponding 13C-13C coupling constants showed a characteristic dependence upon internal rotation of the carbonyl-containing substituent, which may be used to determine predominant rotational conformations of these compounds. A relation between orientation of the C=O bond and 13C-13C coupling constants for the adjacent bonds in oximes was revealed; it may be attributed to hyperconjugation between the corresponding carbon-carbon bond and antibonding orbital of the C=O bond.

13C−13C NMR Spin−Spin Coupling Constants in Saccharides: Structural Correlations Involving All Carbons in Aldohexopyranosyl Rings

13C-13C Spin-spin coupling constants (JCC) have been measured in a group of aldohexopyranoses and methyl aldopyranosides singly labeled with 13C at different sites to confirm and extend prior correlations between JCC magnitude and sign and saccharide structure. Structural correlations for 2JC1,C3, 2JC2,C4, 2JC4,C6, and 2JC1,C5 have been confirmed using density functional theory calculations to test empirical predictions. These geminal couplings depend highly on the orientation of C-O bonds appended to the terminal coupled carbons, but new evidence suggests that 2JCCC values are also affected by intervening carbon structure and C-O bond rotation. 3JC1,C6 and 3JC3,C6 values show Karplus-like dependences but also are affected by in-plane terminal hydroxyl substituents. In both cases, rotation about the C5-C6 bond modulates the coupling due to the alternating in-plane and out-of-plane O6. 3JC3,C6 is also affected by C4 configuration. Both 3JC1,C6 and 3JC3,C6 are subject to remote effects involving the structure at C3 and C1, respectively. New structural correlations have been determined for 2JC3,C5, which, like 3JC3,C6, shows a remote dependence on anomeric configuration. Investigations of dual pathway 13C-13C couplings, 3+3JC1,C4 and 3+3JC2,C5, revealed an important additional internal electronegative substituent effect on 3JCC in saccharides, a structural factor undocumented previously and one of importance to the interpretation of trans-glycoside 3JCOCC in oligosaccharides.

Configurational assignment of carbon, silicon and germanium containing propynal oximes by means of 13C1H, 13C13C and 15N1H spin–spin coupling constants

Configurational assignment of five carbon, silicon and germanium containing propynal oximes has been carried out by means of experimental measurements and high-level ab initio calculations of their 13C-1H, 13C-13C and 15N-1H spin-spin coupling constants. The title compounds were shown to exist in the nonequilibrium mixture of E and Z isomers with the energy difference of less than 0.3 kcal/mol calculated at the MP2/6-311G** level.

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.

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXVI. Stereochemical Study of the Septanose Ring

13C-13C Spin-spin coupling constants of aldoseptanoses of the Dseries were calculated in terms of the self-consistent finite perturbation theory. General relations holding in the stereochemical behavior of the 13C-13C coupling constants in the septanose ring were determined, which made it possible to perform conformational analysis and assign configuration of the anomeric centers in carbohydrates and products of their metabolism.

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXV. Stereochemical Study of the Furanose Ring

Theoretical conformational analysis and calculation of 13C-13C spin-spin coupling constants of aldofuranoses of the D-series were performed in terms of the self-consistent finite perturbation theory in the INDO approximation. All the examined furanoses were found to prefer an envelope conformation. The main factor responsible for the stereospecificity of the 1J1,2 coupling constant is mutual orientation of the hydroxy groups on C1 and C2: s-trans isomers are characterized by greater 1J1,2 values (by 2-4 Hz) than the corresponding s-cis isomers.

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXIV. Nonempirical Calculations: Small Heterocycles

An ab initio calculation was carried out for 13C-13C spin-spin coupling constants in a series of saturated three- and four-membered heterocycles within a framework of second order perturbation theory using an approximation of second order polarization propagator. The accounting for electron correlation effects and the use of correlation-consistent basis sets with addition of functions allowing for internal correlation and of dense functions on nuclei permitted to obtain good quantitative agreement with experimental data.

13C-13C Spin-Spin Coupling Constants in Structural Studies: XXXI. Bicyclo[2.1.0]pentane Heteroanalogs

13C-13C spin-spin coupling constants and orbital hybridization of the bridging bond in bicyclo[2.1.0]pentane heteroanalogs and their unsaturated derivatives were calculated in terms of the self-consistent finite perturbation theory (SCPT INDO). The results showed that the bridging CAC bond in all the examined compounds has an anomaloulsy low s character.

Orientation of the unshared electron pair of the nitrogen atom in N-substituted 2,5-dimethyl-4-piperidinones

The axial orientation of the unshared electron pair of the nitrogen atom in cis isomers of N-substituted [R=H, CH3, CH2C6H5, or C(CH3)3] 2,5-dimethyl-4-piperidinones was proven by using the stereospecificity of the direct 13C-13C spin-spin coupling constants, vicinal 13C-1H spin-spin coupling constants, and two-dimensional nuclear-Overhauser-effect spectroscopy (NOESY).

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.

13C-13C spin-spin coupling constants in six-membered ring azaaromatic compounds

The 13C-{1H} NMR spectra of monomethyl substituted diazines, protonated at the picoline and 2-methylopyrimidine nitrogen atoms, have been analyzed, along with that of pyridine N-oxide and its 2-methyl derivatives protonated at the oxygen atom. Direct and vicinal 13C-13C spin-spin coupling constants (SSCC) have been measured. It was found that the 13C-13C SSCC in diazines follow additivity rules which are based on consideration of the number and mutual orientation or distribution of nitrogen atoms in the ring. It has also been demonstrated that increased direct 1JCC values involving methyl group carbon atoms in α-positions to nitrogen atoms in the aromatic ring are due to effects associated with unshared electron pairs.

Three-dimensional structure of 2-pyrazolines from the results of a study of the 13C-13C spin-spin coupling constants (SSCC)

Three-dimensional structure of 2-pyrazolines from the results of a study of the 13C-13C spin-spin coupling constants (SSCC)

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.

Carbon-carbon coupling constants - a new guide in the stereochemistry of oximes

A positive contribution of more than 7 Hz to the direct 13C-13C spin-spin coupling constants induced by the proximity of the nitrogen lone pair in syn-orientation to the coupled nuclei allows an unambiguous configuration assignment of diverse oximes.