Hochauflösungs-13c-nmr-spektroskopie—III: Strukturabhängigkeit der vicinalen methyl-13c,h-kopplungen in methylazulenen,methylaceheptylenen und anderen methyl-sub stituierten polycyclen mit fünf- und siebengliedrigen ringen

The vicinal couplings of ring hydrogens to methyl C atoms (³J_CH3H) in 22 methyl substituted non-benzenoid polycyclic conjugated hydrocarbons have been determined from the undecoupled ¹³C NMR spectra and have been correlated with bond lengths as well as with the corresponding vicinal H,H couplings, which are taken partly from own ¹H NMR analysis and partly from literature. As a result the (³J_CH3H) couplings of sterically unperturbated methyl groups in 7-membered rings are proportional to the corresponding ³J_HH values which is indicative of comparable influences, but both types of vicinal couplings are not dependent on bond lengths only. Moreover they are to a large extent determined by the CCH bond angles θ and θ', which show a significant variation in condensed 7-membered rings so that this twofold dependence has to be taken into account for structure determinations.     

High resolution proton coupled 13C spectrum and structure of butadieneiron tricarbonyl

A complete analysis of the proton coupled ¹³C spectrum of butadieneiron tricarbonyl is presented. The structure of the diene ligand is discussed on the basis of vicinal C,H and H,H coupling constants as well as ²J(HH), ¹J(CH) and ¹J(CC) data. These data are interpreted in terms of a non-planar C,H skeleton in which C,C bond lengths are nearly equal and the terminal carbon atoms exhibit some rehybridization towards sp³. The results obtained from the complex in solution agree with a structural model from X-ray data of substituted butadieneiron tricarbonyl complexes.     

13C?13C coupling constants in diacetylene (1,3-butadiyne) and its bis(triethylsilyl) derivative

Completely ¹³C-labelled diacetylene and its bis(triethylsilyl) derivative have been synthesized and all the possible spin–spin couplings between the acetylenic carbon nuclei have been determined from their Fourier transform ¹³C NMR spectra. J(CC) values in diacetylene have been also computed by means of the finite perturbation INDO method. Carbon–proton coupling constants in diacetylene have been determined from the spectrum at natural abundance. It has been established that J(CC) values across the triple bond in diacetylene and bis(triethylsilyl)diacetylene are greater than in acetylene and triethylsilylacetylene, respectively. The increase is interpreted in terms of σ- and π-electronic changes which occur with the coupling of two isolated triple bonds into a dimer-like system. All CC coupling constants are greater in diacetylene than in bis(triethylsilyl)diacetylene, which indicates that strong (p→d)π interaction takes place in the latter compound.     

Stereochemical behavior of geminal and vicinal 77Se–13C spin–spin coupling constants studied at the SOPPA(CC2) level taking into account relativistic corrections

A systematic theoretical study of geminal and vicinal ⁷⁷Se–¹³C spin–spin coupling constants in the series of the open‐chain selenides and selenium‐containing heterocycles revealed that relativistic effects play an essential role in the selenium–carbon coupling mechanism, especially when the coupling pathway includes a triple bond, contributing to about 10–15% of their total values and noticeably improving the agreement of the calculated couplings with experiment. Both geminal and vicinal ⁷⁷Se–¹³C spin–spin coupling constants show marked stereochemical behavior as documented by their calculated dihedral angle dependence that could be used as a practical guide in stereochemical studies of organoselenium compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

13C?C13 coupling constants in dimethyl phthalate and phthalic anhydride. Determination of signs—III

Relative signs of ¹³C? ¹³C coupling constants between ring carbons and carbonyl carbons in dimethyl phthalate and phthalic anhydride, ¹³C-labelled in both carbonyl groups, have been determined. The two-and three-bond coupling constants are shown to be positive, whereas four-bond coupling constants are negative. Substituent effects on carbon-carbon couplings due to a carboxyl group have been determined and effects of 5-membered ring formation in phthalic anhydride have been observed.     

Precise values of the 13C component vicinal coupling constants for calculating side-chain conformations in amino acids

From consideration of ¹H–¹H vicinal coupling constants and ¹³C? ¹H long-range coupling constants in a series of amino acid derivatives, the precise values of ¹³C component vicinal coupling constants have been calculated for the three minimum energy staggered rotamers for the C(α)H? C(β)H₂ side-chains of amino acids.     

13C-19F couplings and 19F NMR shifts of cycloalkyl,bicycloalkyl and steroid monofluoro compounds1

The stereospecifity of ¹³C-¹⁹F couplings is investigated with 20 alicyclic compounds. One bond couplings, ranging from 168 to 214 Hz, can be represented as a function of the corresponding ¹³C-H coupling constants. For comparison ¹³C-¹H couplings are determined for norboraane and adamantane and indicate considerable s character at the bridgehead C-H bond of the latter compound. One bond and geminal couplings (ranging from 18 to 24 Hz) are found to depend not significantly on the steric environment. With vicinal couplings a strong dependence is established on torsional angles, which is fitted to a Karplus function. Typical values for CCCF trans arrangements are around 10 Hz, for gauche angles less than 1.5 Hz. Vicinal couplings are substantially altered by electronegative substituents and by hybridization changes of participating carbon atoms. The ³J values observed with cycloalkylfluorides are interpreted on the basis of model geometries for the corresponding hydrocarbons. The influence of solvent and temperature changes is restricted to one bond couplings. ¹⁹F shifts in cyclohexane derivatives are constantly at higher field for axial fluorine (by ~20 ppm), but otherwise there is no significant relation to the orientation of neighbouring bonds, nor to ¹³C shifts of the Cα-F carbon atoms or to the corresponding one bond couplings.     

Long range 13C?13C coupling constants. A review

A large number of ¹³C? ¹³C coupling constants from a diversity of compounds are now available. Attempts have been made to classify this information in order to illustrate how these data are obtained, how signs are determined and how both two- and three-bond couplings can lead to structural information. Coupling constants in aromatic compounds are now well documented, substituent effect trends have been established and correlations with bond orders are noticed. Comparison of ¹³C? ¹³C couplings with ¹³C? ¹H couplings is mentioned. Theoretical calculations are dealt with, and these can now be properly evaluated as both magnitudes and signs of the experimental couplings are known. Finally, the occurrence of long range couplings in biosynthetic material is briefly surveyed.     

1H- und 13C-NMR.-Spektren von 6-(p-X-Phenyl)fulvenen. Kurzmitteilung

¹H- and ¹³C-NMR.-spectra of 6-(p-X-phenyl)fulvenes The ¹H- and ¹³C-NMR.-spectra of a series of 6-(p-X-phenyl)fulvenes 3 , measured at 9.39 T (93.9 kgauss), have been analyzed. In these compounds, electronic effects due to the substituent X clearly exert changes in chemical shifts as well as in coupling constants in the 5-membered ring. Small changes in bond length are observed by comparison of the vicinal ¹H, ¹H-coupling constants, whereas changes in charge densities linearly influence the chemical shifts of C(5), C(2) and C(3).     

The structural dependence of 13C, 13C coupling constants in cyclopropanes

The smallest one-bond carbon—carbon coupling constants of cyclopropane derivatives have been measured for [1-¹³C]cyclopropane-1,1-dicarboxylic acid and cyclopropanecarboxylic acid. The ¹³C, ¹³C coupling constants of cyclopropylcarbinol have also been determined. The dependence of ¹J(CC) of the three-membered ring on different substituents and hybridization effects is evaluated. The carbon—carbon coupling constant of the unsubstituted cyclopropane is discussed on the basis of self-consistent perturbation theory (SCPT) and s character calculations (localized bond orbitals), and the results are compared with the experimental finding. It is shown that the ¹J (CC) can be interpreted by assuming a dual-pathway coupling mechanism.     

13C?13C coupling constants and substituent effects on 13C chemical shifts in 13C labelled pyrene and pyrene derivatives

Long range inter-ring ¹³C? ¹³C couplings are found to be effective in the title compounds, and the magnitudes of coupling constants and of substituent effects on ¹³C chemical shifts, as well as the signs of the latter, alternate with respect to the number of connecting bonds.     

1H, 13C and 19F NMR studies on fluorinated ethers

The enflurane and ethoxyflurane ¹H, ¹³C and ¹⁹F NMR spectra are examined—including sign determination of FF and FH couplings—and considered in the light of previously reported results for methoxyflurane. Conformational differences between methoxyflurane and the former two molecules are indicated by through space FH coupling constants and by the nonequivalence of geminal fluorine nuclei. Populations of conformers about the CC bond are estimated.     

13C, 13C coupling constants in phenyl substituted ethylene,naphthalene, phenanthrene and cyclopentadienone. Dependence on dihedral angles. Determination of signs by the symmetrical double labelling (SDL) method. IV

Carbon-13, carbon-13 coupling constants and carbon-13 chemical shifts have been measured in a series of phenyl substituted ethylenes and aromatics all doubly labelled with ¹³C at the olefinic positions (α,β-) or at neighbouring aromatic positions, tetraphenylcyclopentadienone labelled at the 3,4-positions, and dichlorodiphenylmethane labelled at the α-carbon. Signs of coupling constants were determined by the symmetrical double labelling (SDL) method. Coupling constants over as many as five bonds are reported. Two-bond couplings between carbons in the aromatic skeleton belong to different classes according to the nature of the coupling path. The magnitudes of three-bond coupling constants between such carbons correlate linearly with π-bond orders and a separation of the δ- and π-contributions is evident. The three-bond couplings between the 2-position in a phenyl substituent and the olefinic β-position or a corresponding aromatic position depend on the out-of-plane twist of the phenyl ring and may lead to information about the twist angle. Contrary to findings with aromatic carbonyl compounds two- and three-bond couplings to the α-carbon in the present compounds are fairly constant. The reported data suggest that the signs of coupling constants over more than two bonds alternate in aromatic systems. Carbon-13, carbon-13 coupling constants in naphthalene have been calculated by the INDO-SOS method.     

One‐bond 13C–13C coupling constants in alkyl‐substituted cyclopropenes: experimental and theoretical studies

Measurements of one‐bond carbon–carbon coupling constants, ¹J(C, C), were performed for two series of compounds, alkyl‐substituted cyclopropenes and cyclopropanes. The experimental data were complemented by a set of DFT‐calculated J couplings for the parent cyclopropene ( 1 ), its methyl and silyl derivatives and, additionally, for 1‐methylcyclobutene ( 3 ), 1‐methylcyclopentene ( 4 ) and 1‐methylcyclohexene ( 5 ) and good agreement was observed between the experimental and the calculated data; all the trends are perfectly maintained, including a dramatic decrease in the couplings across endocyclic single bonds in cyclopropene and its derivatives, and a significant decrease in the corresponding couplings in cyclobutene. Using the data obtained, the s characters of the carbon hybrid orbitals involved in the formation of the cyclopropene were calculated. The results clearly show that the ring closure and the related strain exerted upon the cyclopropene molecule only slightly disturb the electron structure of the double bond. The s character of the corresponding carbon orbital is 0.314 in cyclopropene vs the theoretical value of 0.333 in ethene. This is at variance with the endo‐ and exocyclic single bonds, where the s characters of the orbitals forming the endocyclic single bonds are much smaller than those of the bonds in the open‐chain compounds, i.e. 0.229 (C‐1 and/or C‐2) and 0.166 (C‐3). The s values calculated for the exocyclic CH bonds are 0.334 for C‐3 and 0.456 for C‐1 and/or C‐2. Copyright © 2002 John Wiley & Sons, Ltd.     

1H, 13C, 31P NMR and conformational study of 7-membered ring organophosphorus compounds. 1,3,2-dioxaphosphepanes

The ¹H, ¹³C and ³¹P NMR data of several 2-R-2-thiono-1,3-dioxa organophosphorus molecules with 7-membered rings [R = Cl, OC₆H₅, C₆H₅, CH₃, N(CH₃)₂] are reported. The conformation of the 7-membered ring is discussed by reference to the ³J(POCH) coupling constants which are compared with those observed in 6-membered 1,3,2-dioxaphosphorinanes. It is shown that caution must be exercised in using the ³J(POCH) angular dependence as a stereochemical tool. The ³¹P spin lattice relaxation times of some of these 7-membered rings have been measured and the values are discussed.     

Assignment of indirect 13C, 1H couplings in the 13C NMR spectra of some purine and pyrimidine nucleosides and their analogues by long-range selective 1H decoupling

The assignments of the long-range ¹³C, ¹H coupling constants in the ¹³C NMR spectra of the base moieties of several purine and pyrimidine nucleosides and their analogues were established by the application of long-range selective ¹H decoupling with low-power ¹H irradiation. The ³J values between the carbons and protons of the pyrimidine ring in these compounds were larger than the ²J values. The conformational preference of these nucleosides in solution was shown to be predominantly anti from the value of the vicinal ¹³C, ¹H coupling constants between H-1′ and the base carbons through the glycosidic bond.     

Application of 1H and 13C NMR to the structural elucidation of tetrahydroquinoxalines condensed with five-membered heterocycles

¹H and ¹³C NMR spectral data for 21 N-methyltetrahydroquinoxalines annelated with furan, pyrrole, imidazole or thiazole rings are reported. Unambiguous assignments of the ring junction ¹³C resonances were made on the basis of selective decoupling experiments and with the aid of one-bond and long-range ¹³C–¹H coupling constants. The effects of five-membered heterocycles on the ¹H and ¹³C chemical shifts of the ring junction hydrogen and carbon atoms are considered. Values of one-bond ¹J(CH) and vicinal ³J(HH) coupling constants between the ring junction protons are also discussed as a diagnostic means for structural elucidation of tetrahydroquinoxalines condensed with five-membered heterocycles.     

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 CÄC bond in all the examined compounds has an anomaloulsy low s character.     

1H and 13C NMR studies on 1,3,2-dioxarsolanes

The ¹H and ¹³C NMR spectra of a series of 1,3,2-dioxarsolanes have been obtained at 2.1 T and some at 9.4 T. The chemical shifts and spin-spin coupling constants have been obtained from complete spectral analyses of the ¹H and proton-coupled ¹³C spectra. The spectral data are interpreted on the basis of two rapidly interconverting half-chair conformers with a pseudoaxial substituent at arsenic. Unique assignment of syn/anti or cis/trans geometries have been made from ¹H or ¹³C NMR spectroscopy alone. The syn and trans isomers of the 4-methyl- and 4,5-dimethyl-1,3,2-dioxarsolanes, respectively, appear to be conformationally biased towards the forms with pseudoequatorial methyl groups. The general trends in the geminal and vicinal ¹H? ¹H and ¹³C? ¹H coupling constants are interpreted in terms of stereospecific, electronegativity and lone-pair effects of the oxygen heteroatoms and conformational factors. The NMR data on the 1,3,2-dioxarsolanes are discussed with reference to related 1,3-dithoxa- and 1,3-dithia- five-membered rings with As, P, S or C at the 2-position.     

The conformational dependence of vicinal 13C13C spin–spin coupling constants in alicyclic compounds

A series of alicyclic compounds with dihedral angles of 0°, 60°, 90°, 120° and 180° between a ¹³C-labelled carbon atom and a carbon atom separated by three bonds from the label has been synthesized. The vicinal ¹³C¹³C spin coupling constants were measured, and from the results a Karplus-type relationship between ¹³C¹³C spin coupling and dihedral angle is proposed.