Long-range Spin Spin Coupling Constants Research Articles

Probing long-range spin-spin coupling constants in 2-halo-substituted cyclohexanones and cyclohexanethiones: The role of solvent and stereoelectronic effects.

Earlier studies with 2-bromocyclohexanone demonstrated a measurable long-range coupling constant (4 JH2,H6 ) for the equatorial conformer, although 4 JH2,H4 and 4 JH4,H6 were not observed; as a consequence, it is inferred that the carbonyl group plays an important role particularly due to hyperconjugative interactions σC2H2 →π*C═O and σC6H6 →π*C═O. In the present study, NBO analysis and coupling constant calculations were performed to cyclohexanone and cyclohexanethione alpha substituted with F, Cl, and Br, aiming to evaluate the halogen effect and acceptor character of the π* orbital on the long-range coupling pathway. The σC2H2 →π*C1═Y and σC6H6 →π*C1═Y (Y═O and S) hyperconjugative interactions for the equatorial conformer indeed contribute for the 4 JH2,H6 transmission mechanism. Surprisingly, the 4 JH2,H6 value is higher for the carbonyl compounds, although the interactions σC2H2 →π*C═Y and σC6H6 →π*C═Y are more efficient for the thiocarbonyl compounds. Accordingly, the Fermi contact (FC) contribution for the thiocarbonyl compounds decays deeper than in ketones, thus reducing more the 4 JH2,H6 values. Moreover, both πC═S →σ*C─X and πC═S →σ*C─H interactions seem to be stronger in thiocarbonyl than in carbonylic compounds. The implicit solvent effect (DMSO and water) on the coupling constant values was negligible when compared with the gas phase. On the other hand, an explicit solvent effect was found and 4 JH2,H6 for the thiocarbonyl compounds appeared to be more sensitive than for the cyclohexanones.

Long‐range JCH heteronuclear coupling constants in cyclopentane derivatives. Part II

Here we report the detailed measurement of long-range heteronuclear spin-spin coupling constants, especially 2, 3JCH spin-spin couplings for eight different cyclopentane derivatives. These 2, 3JCH constants were shown to be a useful tool in the determination of the relative stereochemistry in these rings. The coupling constant measurements reported here are based on two different experiments: a 2D heteronuclear correlation experiment named G-BIRDR, X-CPMG-HSQMBC and the 2D-coupled gHSQC {1H-13C} experiment

Long‐range JCH heteronuclear coupling constants in cyclopentane derivatives

Detailed measurements of long-range heteronuclear spin-spin coupling constants, especially (2, 3)J(CH) spin-spin couplings for various cyclopentane derivatives, are reported. The measurements are based on a 2D heteronuclear correlation experiment named G-BIRD(R, X)-CPMG-HSQMBC.

The tautomeric equilibrium and stereochemistry of β-sulfonyl enamines

Compounds of three groups of parent secondary aliphatic β-sulfonyl enamines, unsubstituted or with an alkyl substituent in the α or β positions, have been studied. The β-sulfonyl enamines are found in equilibria between the E and Z enamine and imine forms in varying amounts in CDCl3 solution. 1H, 13C and 15N data were acquired and used for the assignment of the three species in solution. Considerable variations in the amounts of enamine E and Z and imine forms are found, depending on the substitution pattern. The conformational space of the equilibrated tautomers have been investigated using steady-state NOE experiments, dynamic NMR and nJ(H,H) and nJ(C,H) long-range spin-spin coupling constants, as well as ab initio HF and DFT calculations for structure determination and relative energy evaluations. Based on NOE, saturation transfer experiments and conformational analysis, an equilibrium scheme is proposed showing the mechanism and the involvement of water in the transformation of β-sulfonyl imines into the corresponding enamines.

13C and19F NMR study of α,β-difluorostyryl derivatives of transition metal carbonylates. A method of signal assignment based on the carbon—fluorine spin-spin coupling constants

The13C and19F NMR spectra ofZ- andE-isomers of β-X-substituted α,β-difluorostyrenes (X=F, Cl, CpFe(CO)2, Re(CO)5, Re2(CO)9Na) were studied. Direct and long-range (across 1–5 bonds) spin-spin coupling constants and the (13C−12C) isotope shifts in the19F NMR spectra were determined. The study of the13C satellites in the19F NMR spectra of substituted difluorostyrenes permitted assignment of the13C NMR signals of the vinylic carbon atoms. Similarly, the signals in19F NMR spectra were assigned based on coupling constants of fluorine withipso-carbon. These assignments were found to be in good agreement with the data available from the literature (X=F, Cl). The developed approach was applied to the elucidation of the structure ofZ−PhCF=CClFe(CO)2Cp.

1H, 19F, and 13C nuclear magnetic resonance approaches to the barrier to rotation about the Csp2—Csp3 bond in 1,1,1 -trifluoro-2-phenylethane. Proximate coupling constants and molecular orbital computations

The 1H, 19Fand 13C{1H} nuclear magnetic resonance spectra of 1,1,1-trifluoro-2-phenylethane, 1, in CS2–C6D12, acetone-d6, and benzene-d6 solutions, on analysis, yield long-range coupling constants from which are derived the apparent twofold barriers to rotation about the Csp2—Csp3 bonds. The twofold barrier is 9.0(2) kJ/mol, independent of solvent, 4.0 kJ/mol larger than that of ethylbenzene, also independent of solvent. The theoretical barrier heights for the free molecules at the post-Hartree–Fock level of molecular orbital theory (frozen-core MP2/6-31G*) also differ by 4 kJ/mol, but are about 1 kJ/mol higher than the experimental estimates. The perpendicular conformer is the most stable for both molecules. Comparisons are made with the benzyl halides, in which the internal barriers are remarkably sensitive to solvent. A spin–spin coupling constant over five formal bonds, 5J(H, F), involving the ortho protons in 1, is +0.74(2) Hz and is discussed in some detail in terms of its dependence on intenuclear distances (possible through-space interactions). The solvent perturbations of 3J(H, F) and of 2J(C, F) are of opposite sign. Other long-range coupling constants or their absence are also pointed out. For example, those between 19F and 13C nuclei or protons at the meta position are effectively zero; at the para position they are significant. Keywords: 1,1,1-trifluoro-2-phenylethane; 1H, 19F, and 13C NMR; long-range spin-spin coupling constants; through-space 1H, 19F spin–spin coupling constants; internal rotational potential; molecular orbital computations of internal potential.

Remarks on the barrier to rotation about the Csp2—O bond in anisole

Molecular orbital computations with the basis set 6-31G are reported for seven values of θ, the torsion angle about the [Formula: see text] bond in anisole. All bond angles and lengths are optimized but the atoms of the phenyl group are constrained to a plane. The relative energies are fit by V(θ)/kJ mol−1 = 7.78(5) sin2θ + 2.41(5) sin2 2θ − 0.54(5) sin2 3θ, where θ is zero when the heavy-atom skeleton is planar. Computations with the basis set 6-31G*(5D) for three values of θ can be reproduced by V(θ)/kJ mol−1 = 6.07 sin2θ + 2.68 sin2 2θ. These results are compared with experimental gas phase data from the literature. The analysis of the 1H nuclear magnetic resonance spectrum of anisole-α-13C in aCS2/C6D12/TMS solvent mixture yields a value of 6J(1H, 13C), the long-range spin-spin coupling constant between the 13C nucleus in the methyl group and thepara proton. Because this coupling constant is proportional to sin2 θ, it is shown, together with previous dynamic nmr measurements, that the barrier to rotation about the [Formula: see text] bond in solution cannot be purely twofold. The internal potential must also contain a fourfold term of the same sign as that of the twofold component. If the V2/V4 ratio given by the various molecular orbital computations holds in solution, then V2 is 15.0 ± 2.0 kJ/mol and V4 is 5.6 ± 2.2 kj/mol. The apparent doubling of the internal barrier in solution is perhaps unprecedented for such a simple molecule. Keywords: anisole, internal barrier in solution, anisole-α-13C, 1H NMR, conformational behaviour, MO computations.

Structure of lilidine

The new alkaloid lilidine, isolated for the first time from the epigeal part ofLilium martagon has been studied by special methods. It has the composition B5H6NO2, mp 118–110°C, [α]D-26.3°. The1H and13C NMR spectra were studied in detail. The values of the direct and long-range spin-spin coupling constants between the13C carbon nuclei and the1H nuclei of the alkaloid molecule were measured with the aid of13C-[{su1}H] selective heteronuclear double resonance. The structure of 5-hydroxy-3-methyl-3-pyrrolin-2-one is suggested for lilidine.

Long-range spin-spin coupling and relative orientation of vinyl group in 1-venylpyrazole

On the basis of the experimental values of the long-range spin-spin coupling constants of the protons it was established that in 1-vinylpyrazole and its 4-bromo derivative the vinyl group has predominantly a trans orientation relative to the nitrogen in the 2 position.

13C-NMR studies on halomethylvinyl chrysanthemic acids and esters - spin-lattice relaxation time and 13C - 1H coupling constants.

New types of stable chrysanthemic acids and esters were synthesized, and their 13C-NMR were examined and fully analyzed. The configurations of the cyclopropanecarboxylic acid and halomethylvinyl group were reflected on the spin-lattice relaxation time of the substituted methyl carbon involved in their structure. The long-range spin-spin coupling constants (3JCH) correlated well to the NOE and T1 measurements, which can generally be used to distinguish the geometry of the substituted double bond.

Application of NMR spectroscopy for the study of the three-dimensional structures of hydrogenated heterocycles (review)

A review of the dependences of the direct, geminal, vicinal, and long-range spin-spin coupling constants on the valence, dihedral, and torsion angles, and on the electronegativities and orientations of the heteroatoms is given. The empirical and nonempirical dependences for the constants with participation of the nuclei of the 1H, 13C, 14N, 15N, 19F, 31P, 29Si, 119Sn, and 199Hg isotopes are presented.

Concerning the long-range proton-proton spin-spin coupling constants and the internal rotation barrier in styrene

Concerning the long-range proton-proton spin-spin coupling constants and the internal rotation barrier in styrene

Long-range carbon-carbon spin-spin coupling constants in carboxyl labeled aromatic carboxylic acids and dihydro aromatic carboxylic acids

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLong-range carbon-carbon spin-spin coupling constants in carboxyl labeled aromatic carboxylic acids and dihydro aromatic carboxylic acidsJames L. Marshall, Larry G. Faehl, Arthur M. Ihrig, and Michael BarfieldCite this: J. Am. Chem. Soc. 1976, 98, 12, 3406–3410Publication Date (Print):June 1, 1976Publication History Published online1 May 2002Published inissue 1 June 1976https://doi.org/10.1021/ja00428a002RIGHTS & PERMISSIONSArticle Views160Altmetric-Citations24LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (590 KB) Get e-Alerts Get e-Alerts

A nuclear magnetic resonance determination of the barrier to internal rotation in phenylethane

The long-range nuclear spin-spin coupling constant between the methylene protons and the ring protons at the para position in 3,5-dibromo-phenylethane in benzene solution is consistent with a two-fold barrier of 1.2 ± 0.1 kcal/mole to rotation about the sp 2-sp 3 carbon-carbon bond, in agreement with thermodynamic data on phenylethane and with deductions based on hyperfine interactions in related radical anions. The low-energy conformation has a plane of symmetry, the methyl group being situated out of the aromatic plane, in disagreement with Raman depolarization data interpretations and with deductions based on proton chemical shifts.

Proximity and bond orientation effects on long-range proton-fluorine nuclear spin-spin coupling constants

Proximity and bond orientation effects on long-range proton-fluorine nuclear spin-spin coupling constants

Utilization of N15H1 heteronuclear spin ? Spin coupling constants for the investigation of the three-dimensional structures of oximes of furfural and p-bromophenylfurfural and their O-acetyl derivatives

On the basis of the large difference in the 2JN15Hald values for the E and Z isomers, the configurations of the isomeric oximes of furfural and p-bromophenylfurfural and their O-acetyl derivatives were determined. The stereospecificity of the long-range spin-spin coupling constants of the nitrogen atom and the H4 proton of the furan ring (5JN15H4) was investigated, and the possibility of the utilization of these constants for the stereochemical analysis of oximes of the furan series was shown.

Isomerism of 5-arylfurfural oximes (according to PMR spectroscopic data)

The stereochemistry of 5-arylfurfurals and their O-acetyl derivatives was studied by PMR spectroscopy. The configurations of each of the isomers were determined for the oximes of p-bromo- and p-chlorophenylfurfurals, which were isolated as two geometrical isomers, and also for their O-acetyl derivatives. The anti and syn configurations were established for the oximes of phenylfurfural and p-nitrophenylfurfural, respectively, which were obtained as single isomers. Conclusions regarding the preferred conformation of the side chain relative to the plane of the furan ring in all of the investigated isomers were drawn on the basis of an analysis of the of the long-range spin-spin coupling constants (\({\text{J}}_{{\text{H}}_{\text{0}} {\text{H}}_{\text{4}} } \)).

The signs of the long-range spin-spin coupling constants in methyl pyridines as determined by the INDOR technique

The long-range spin-spin coupling constants between the methyl and the ring protons in several methyl pyridines have been determined, with their signs. The INDOR technique was used for this purpose and a systematic method was developed applicable to these spin systems, which were all of the ABCX 3 type. It was found that 6J H,CH 3 and 4J H,CH 3 are negative, while 5 J H, CH 3 is positive, with | 4 J|>| 6 J|>| 5 J|. These results show the same trend as shown by investigations of previous authors in other cyclic compounds.

Nuclear magnetic resonance of organophosphorus compounds: Signs and magnitudes of long-range 1H31P spin-spin coupling constants in methyl-substituted trithienylphosphine derivatives

The signs and magnitudes of the long-range spin-spin coupling constants between the methyl protons and ring phosphorus nuclei in the six isomeric methyl-substituted trithienylphosphines and their sulfides have been determined. The signs of the coupling constants were obtained using homonuclear selective decoupling and spin tickling techniques and the double resonance spectra compared with those theoretically calculated. In the phosphines the observed JCH3P coupling constants are all positive. In the phosphine sulfides a change in sign is observed in most cases for these couplings, all signs being similar to those of the corresponding methyl-proton-ring-proton couplings in methylthiophenes. The signs and magnitudes are discussed in terms of π- and σ-electron contributions to the couplings. Evidence is obtained for a positive effective hyperfine interaction in the CP bond of the phosphines (QCP(III) > 0) and a negative term in the tetracoordinated phosphorus compounds (QCP(V) < 0). Sizeable dependences of the ring-proton-ring-phosphorus couplings on the orientation of the phosphorus lone pair with respect to the ring planes are indicated by the experimental results for the ortho methyl-substituted phosphines.

Nuclear magnetic resonance of organophosphorus compounds: Signs of long-range 1H 31P spin-spin coupling constants in tri-(5-methyl-2-furyl)-phosphine derivatives

The magnitudes and relative signs of the long-range 1H 31P spin coupling constants between the side-chain protons and the 31P nucleus in tri-(5-methyl-2-furyl)-phosphine, its sulfide and methyl phosphonium salt have been obtained. The relative signs were deduced from homonuclear spin tickling and selective decoupling experiments. Upon tetracoordination of phosphorus a change in the sign for this long-range (five- and/or six-bond) coupling is observed. For the phosphine | J PCH 3 | = 0.19 Hz and has the same sign as the 1H 31P ring coupling constants ( 3 J PH(3) and 4 J PH(4)), i.e., positive, whereas for the phosphine sulfide and methyl phosphonium salt | J PCH 3 | equals 0.46 and 0.38 Hz, respectively, and are both of opposite sign to the 1H 31P ring couplings, i.e., negative.