Studies on olefins. IX—proton NMR study of some CH2CR1R2 and CHR3CR1R2 alkenes

The proton NMR spectra of 2,3,4,4-tetramethyl-3-t-butylpent-1-ene rotarners have been completely assigned by low temperature NOE measurements. Chemical shifts and cis and trans allylic coupling constants are unambiguously determined. It is shown that other 2-substituted propenes can be assigned on the basis of the coupling constants, but not from the chemical shift data. In 1,2-disubstituited propenes, however, the transoid coupling constant falls in the range of the cisoid coupling constant values of the 2-substituted propenes. Coupling constants cannot, therefore, be used in the 1,2-disubstituted propene series as a criterion for determining structure.     

PMR spectra of dimers of cyclopentadienyl compounds

The PMR spectra of cyclopentadine endo-dimer, its 1y-acetoxy-derivative and the dimer of spiro-heptadiene have been thoroughly studied. The assignment is proved by the use of spindecoupling experiments and the INDOR-technique. The relative signs of several coupling constants were found and used for the assignment. General trends in the proton chemical shifts and coupling constants are discussed for the derivatives of the cyclopentadiene dimer and for the substituted cyclopentadiene dimers.     

Spectroscopic studies on olefins. VII–propene and 3-methylbutene-1; proton NMR coupling constants as a function of solvent and temperature in relation to molecular geometry

The proton spectra of the compounds propene (1) and 3-methylbutene-1 (2) have been measured in various solvents and, as neat liquids, at variable temperature. The effects of solvent and temperature on 1 are found to be small, but not negligible. The effect of temperature on the coupling constants of 2 are more pronounced, which is explained in terms of an anti-gauche equilibrium. To obtain a consistent ΔE° value from each temperature dependent coupling constant it is necessary to correct for the non-conformational temperature effects (obtained from 1) as well as to correct for changes in the geometry of the entire molecule, which are concurrent with a conformational transition. Such geometry changes have been calculated by a consistent force field technique, which, when coupled with INDO-MO calculated dependencies of coupling constants on valence (and torsional) angles, provided the changes in coupling constants. The observed temperature dependence of the coupling constants of the H₂C?CH— moiety of 2 could be satisfactorily explained in this fashion. The difference in energy between the anti and gauche forms of 2 were determined as ΔE° = 127 ± 14 cal mol^?1.     

Measurements of Long-Range Homonuclear Coupling Constants

Coupling constants in proton systems provide access to useful structural information. Several methods have been proposed to measure these constants in high-resolution spectra, but many of them are not well suited when the coupling constants are comparable to the spectral linewidth. In such a case the measurement of the apparent splitting, obtained from conventional NMR or from two-dimensional correlation spectroscopy (COSY), can cause a miscalculation of the true coupling constant value. In this work, data processing for extracting small coupling constants is described. Signals are obtained from spin-echo experiments and analysed in the time domain in such a way that couplings are apparently multiplied by n+1, where n is positive. Small coupling constants in 4-methyl-1,3-dioxane were obtained by this method. © 1997 John Wiley & Sons, Ltd.     

Stereochemical characterization of some mono- and diaryl substituted ethylene oxides by NMR spectroscopy

NMR spectra of several styrene, stilbene and stilbazole oxides have been determined, and chemical shifts and coupling constants have been correlated with cis-and trans-configurations. Assignments have been made for all protons, and double resonance technique and ¹³C? H coupling constants have been used in some particular cases. An explanation is proposed for the observation that chemical shifts of oxirane protons are higher for cis than for trans isomers.     

Proton magnetic resonance spectra of 2,6-disubstituted naphthalenes

The spectra of several 2-methyl-6-R-disubstituted naphthalenes (R=H, Me, I, NO₂, Cl, SO₂Cl, OH, OMe, COMe, Br, F and NHCOMe), have been analysed. Chemical shift and coupling constant values of these compounds are presented. The proton chemical shifts have been found to correlate with the ortho parameter, Q.     

Carbon-13 NMR spectra of some phenanthrene derivatives from Aristolochia indica and their analogues

¹³C NMR spectra of compounds related to aristolochic acid and aristololactam, the constituents of Aristolochia indica, have been studied to determine the chemical shifts and coupling constants of polysubstituted phenanthrenes. Selective ¹H decoupling and long-range couplings were utilized for the assignments. Substituent-induced chemical shifts and also the effects on coupling constants could be deduced in some cases. Anion formation was found to be particularly helpful in the interpretation of the spectra of carboxylic compounds. Shift assignments of some structurally related compounds could also be made.     

Additivity of substituent effects on the proton-proton coupling constants of disubstituted pyridines

From the spin-spin coupling constants of pyridine and monosubstituted pyridines the effects of several substituents have been calculated- Assuming an additivity relationship when two of these substituents are present in the same molecule, the spin-spin coupling constants for 11 disubstituted pyridines have been calculated.The NMR spectra of 13 disubstituted pyridines have been studied to obtain accurate values of their coupling constants. The experimental values of these constants are in very good agreement with those calculated using the additivity relationships.     

Solvent dependence of the molecular structure of hydrogen cyanide determined by NMR of partially oriented molecules

The chemical shifts and the direct and indirect spin–spin coupling constants of HCN have been measured in various liquid crystal solvents. The sign of the indirect coupling constant J(¹⁵NH) is found to be negative. The ¹³C shift anisotropy is 334±20 ppm. The molecular structure apparently varies considerably with the solvent used. These solvent effects, which can be attributed to a correlation between vibration and rotation of the molecule, are corrected.     

13C NMR coupling constants in delocalized organo-alkali metal compounds. Models of polymerization systems

2,5-Diphenyl-2,5-dipotassiohexane, 2-lithio-4,4-dimethyl-2-phenylpentane, and 1-lithio-2,5,5-trimethylhexene-2 have been prepared, all labelled with¹³C in the position adjacent to the alkali metal atom. The¹³C NMR spectra of these compounds have been measured and the¹³CC coupling constants found for the charged atom. The first two compounds have coupling constants consistent with an sp² hybridized C_α, with relatively little effect of the charge on the coupling constant. The third compound, when dissolved in either THF or benzene, gave much smaller coupling constants, which are more difficult to interpret.     

Etude des Signes des Constantes de Couplage 3J(P?X?C?H) et 4J(F?P?X?C?H) dans les Diaza-, Dioxa- et Dithiaphospholanes Fluores

The NMR spectra of the trivalent fluorophospholanes ( 1, 2, 3 ) have been analysed at length. The absolute signs of the ³J(P? H) and ⁴J(F? H) coupling constants have been referred to the known negative sign of the ¹J(P? F) coupling constant from selective heteronuclear double resonance experiments. The ³J(P? O? C? H) and ³J(P? N? C? H) coupling are positive. The weak values observed for ³J(P? S? C? H) have opposite signs, the larger being positive. All the ⁴J(F? P? X? C? H) coupling constants are positive showing a lack of stereospecificity.     

NMR study of 4-membered rings. VIII—The sign of the four-bond couplings in adducts of cyclopentenone with vic-dichloroethylenes

The proton spectra of the four stereoisomers prepared by photocycloaddition of 2-cyclopentenone to cis and trans dichloroethylene have been analysed using tickling and INDOR techniques in order to obtain the sign of the cross-ring four-bond coupling constants in the cyclobutane ring. These parameters are correlated with the relative orientation of the protons involved. The complete NMR analysis of the seven-spin system of the cycloadduct endo-7-phenoxybicyclo[3.2.0]hept-2-en-6-one has been carried out and all the four-bond coupling constants have been obtained and discussed. The sign of the cross-ring coupling in the cyclobutanone ring has been determined.     

Fluorine NMR spectra of pentafluorophenyl derivatives

The fluorine chemical shifts and spin-spin coupling constants of 65 pentafluorophenyl derivatives with widely varying organic substituents were examined. Useful correlations of the three meta coupling constants with the chemical shifts of the para fluorine were found. It is suggested that these relationships be extended to all compounds of the type considered in order to determine the signs and approximate values of meta coupling constants. Equations for correlation of the fluorine chemical shifts with the Taft constants are presented. The possibility of calculating the Taft constants from the ¹⁹F NMR spectra of pentafluorophenyl compounds is being discussed.     

Nuclear Magnetic Resonance Studies. IV. Proton Chemical Shifts and Coupling Constants of 2-Norbornanols and Methyl-Substituted 2-Norbornanols

The proton magnetic resonance spectra of the two isomeric 2-norbornanols (I and II) and of eighteen of their methyl-substituted derivatives (III to XX) under the influence of tris(dipivalomethanato)europium, Eu(dpm)₃, have been measured. In all cases linear relationships between the observed shifts and the molar ratios of Eu(dpm)₃ to substrate were realized. The chemical shifts obtained from the extrapolation to zero concentration of Eu(dpm)₃ are in good agreement with the observed values. The coupling constants were found to be essentially unaffected by Eu(dpm)₃. Consequently, determination of a chemical shift by extrapolation or of a coupling constant from the shifted spectrum appears to be justified. Reassignments of a number of signals are discussed. Chemical shifts, normalized induced shifts, and coupling constants are tabulated.     

Group IV organometal derivatives of pyridine. I—A 1H and 13C NMR investigation of trialkylmetal derivatives of pyridine

The proton and carbon-13 NMR spectra of thirteen trialkylmetal derivatives of pyridine, several of which were previously unknown, have been recorded and analysed. The proton NMR spectra show variations in proton chemical shifts but not in proton-proton coupling constants when the metal substituent is changed; the ring proton-metal coupling constants ⁿJ(M? H) in the tin and lead derivatives correspond closely with the corresponding proton-proton couplings ⁿJ(H? H) in pyridine. The carbon-13 chemical shifts of the carbons bound to the metal can apparently be correlated with the electron-donating ability of the trialkylmetal group. In the trimethylstannylpyridines the value of ¹J(Sn? C_ring) varies greatly with the position of the Me₃Sn group.     

Orientational ordering of liquid crystals containing a difluoro-substituted phenyl ring

The orientational ordering of several liquid crystals containing a difluorosubstituted phenyl ring has been studied through the use of C-13 NMR. The fluorinated phenyl ring of these liquid crystals have C_s symmetry, so three order parameters are required to completely describe the ordering of this ring. All three of these order parameters have been calculated from carbon-fluorine dipolar coupling constants obtained from the carbon-fluorine splittings in the C-13 NMR spectra. Because of the complexity of the fluorine-coupled spectra, variable angle spinning (VAS) was used to resolve the carbon-fluorine splittings. In order to study the orientational ordering over wide ranges of temperature, we have developed an empirical correlation between the order parameter and the value of a carbon-fluorine dipolar coupling constant. This enabled us to study the change in the order parameter with temperature. The results of applying this method to several structurally similar liquid crystals containing the same type of difluorinated phenyl ring are presented. A comparison is made to a similar mono-fluorinated liquid crystal.     

13C NMR spectra of non-labelled and 15N-mono-labelled azo dyes

¹³C NMR spectra of four types of azo coupling products from benzenediazonium chloride have been measured and interpreted, viz. hydrazo compounds with an intramolecular hydrogen bond (3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone), azo compounds without an intramolecular hydrogen bond (4-hydroxyazobenzene), azo compounds with an intramolecular hydrogen bond (2-hydroxy-5-tert-butylazobenzene) and an equilibrium mixture of both the tautomers of 1-phenylazo-2-naphthol. The absolute values of the J(¹⁵N¹³C) coupling constants have been determined by recording the spectra of the ¹⁵N isotopomers, and have been used, in some cases, for ¹³C signal assignment. A relationship has been found between the chemical shifts of the C-1′ to C-4′ carbons of the phenyl group (from the benzenediazonium ion) or the ¹J(¹⁵N¹³C) coupling constant, and the composition of the tautomeric mixture.     

Spin-spin coupling and substituent and halogen isotope shift effects in the fluorine NMR spectra of fluorinated cyclopropanes and cyclopropyl ethers

The (19)F NMR spectra of a series of fluorinated cyclopropanes, most of which contain chlorine or bromine on the ring, have been observed and analyzed. A scheme has been developed to assign the resonances and the molecular stereochemistry, based on substituent effects, comparison of related molecules, and isotope shifts induced by the halogens. Replacement of fluorine by chlorine shifts cis fluorine resonances to lower field, and bromine has an even greater downfield influence. However, the shift effect of bromine compared to chlorine on gem or trans fluorines is variable. The magnitude of the isotope shifts is found to be regularly related to the geometrical relationship of the halogen to the observed fluorine and thus makes a significant contribution to the fluorine assignments. The three-bond spin-spin coupling constants between fluorine atoms in cyclopropanes display unusual behavior and are not helpful for assignment of the fluorine resonances. The signs of the coupling constants have been investigated by spin-tickling experiments, and the previously developed relation of the coupling constant sign to its temperature dependence has been found to be violated for some molecules.     

Carbon Magnetic Resonance Spectra of α, β, γ, δ- and α, β, α′, β′- Unsaturated Ketones

Carbon-13 spectra of a series of 26 unsaturated ketones (ortho- and para-cyclo-hexadienones and corresponding open-chain analogues) have been measured by Fourier-transform. Pulse spectroscopy. A complete analysis has been achieved by means of double resonance experiments using noise-modulated and coherent off-resonance proton irradiation and with the aid of non-decoupled spectra. Chemical shifts are interpreted in terms of charge distribution in the dienone system and of methyl substituent effects. Carbon chemical shifts were also obtained for O-protonated ortho- and para-cyclohexadienones. One-bond and long-range carbon-proton and carbon-fluorine spin coupling constants are reported for several compounds.     

1H-NMR-Spektroskopische Untersuchungen an isomeren Alkendiinen

¹H NMR spectra of several aliphatic and phenyl substituted alkenediynes have been obtained. Chemical shifts and coupling constants of these compounds are discussed in conjunction with some compounds described in the literature. Chemical shifts of the protons from isomeric alkenediynes R? C?C? C?C? CH?CH₂, R? CH?CH? C?C? C?CH and R? CH?CH? C?C? C?C? CH₃ (R = H, alkyl, C₆H₅, C₆H₄OCH₃-p) are well correlated with cis/trans-isomerism and electronic effects of substituents at the C?C bond. The coupling constants were found to be only slightly dependent on the substitution at the double bond. We could resolve couplings over a maximum of eight bonds in the alkenediyne system.