J(77Se,1H) and J(77Se,13C) couplings of seleno‐carbohydrates obtained by 77Se satellite 1D 13C spectroscopy and 77Se selective HR‐HMBC spectroscopy

Seleno‐carbohydrates are those in which the oxygen of the glycosidic bond or the hydroxyl group is artificially replaced with selenium. This substitution changes ¹H and ¹³C chemical shifts and produces spin coupling constants involving ⁷⁷Se. Coupling constants, such as ^2‐3J(⁷⁷Se, ¹H), are likely to be useful for conformational analyses of glycans because such couplings are never observed in natural glycans. Several papers have discussed the relationship between ^2‐3J(⁷⁷Se, ¹H) and conformation; however, only few reports describe ^1‐3J(⁷⁷Se, ¹³C), which could also be useful. Here, we obtain ⁷⁷Se coupling constants of seleno‐carbohydrates from ⁷⁷Se‐selective HR‐HMBC and ⁷⁷Se satellites in 1D ¹³C spectra and examine their conformations using the Newman projection scheme.     

13C, 1H spin coupling constants of dimethylacetylene

¹³C, ¹H spin coupling constants of dimethylacetylene have been determined by the complete analysis of the proton coupled ¹³C NMR spectrum. For the methyl carbon ¹J(CH) = + 130.6₄ Hz and ⁴J(CH) = + 1.5₈ Hz, and for the acetylenic carbon ²J(CH) = ? 10.34 Hz and ³J(CH) = +4.30 Hz. The ⁵J(HH) long-range coupling constant (+2.79 Hz) between the methyl protons was also determined.     

A 1H NMR and molecular modelling investigation of diastereotopic methylene hydrogen atoms

The ¹H NMR spectra of methyl 3‐bromo‐2‐methylpropionate (1a) and the corresponding chloro compound (2a) show no long‐range coupling between the methyl and methylene protons. In contrast, in the analogous dihalocompounds, methyl 2,3‐dibromo‐2‐methylpropionate (1b) and methyl 2,3‐dichloro‐2‐methylpropionate (2b), one of the methylene protons exhibits a large ⁴J_HH coupling (0.8 Hz) to the methyl group, but the other proton shows no observable splitting. This can be explained quantitatively by calculations of the conformational preferences in these compounds combined with the known orientation dependence of the ⁴J_HHcouplings. One conformer predominates in the dihalo compounds 1b and 2b, and this is responsible for the ⁴J_HH coupling. In 1a and 2a all three conformers are populated and the ⁴J_HH couplings average to zero. The technique is a potentially general method of unambiguously assigning diastereotopic methylene protons. Copyright © 2002 John Wiley & Sons, Ltd.     

High resolution 13C NMR spectroscopy. IV—stereochemical assignments in butenedioic acids and 3-pentene-2-ones

Vicinal ¹³C, H coupling constants ³J(CO, H) for butenedioic acids and ³J(CH₃, H) for 3-pentene-2-ones have been determined and are correlated with the configuration of the corresponding C?C double bond. For both types the relationship ³J(CH) trans > ³J(CH)cis holds; in the case of the CH₃, H couplings, however, the ³J(CH₃, H) trans values are reduced because of steric reasons, so that configurational assignments seem possible only when both isomers are present. Additionally, the coupling constants ³J(COC H₃,H ) and the chemical shifts δ have been evaluated for the pentenones and it is shown that these parameters give information about the predominating conformation of α, β-unsaturated methyl ketones.     

Conformational Analysis of the Anti‐obesity Drug Lorcaserin in Water: How To Take Advantage of Long‐Range Residual Dipolar Couplings

The conformational state of 8‐chloro‐1‐methyl‐2,3,4,5‐tetrahydro‐1H‐3‐benzazepine hydrochloride (lorcaserin) in water has been determined on the basis of one‐bond and long‐range C? H residual dipolar coupling (RDC) data along with DFT computations and ³J_HH coupling‐constant analysis. According to this analysis, lorcaserin exists as a conformational equilibrium of two crown‐chair forms, of which the preferred conformation has the methyl group in an equatorial orientation.     

1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P?C) and J(P?H)

All J(P? H) and J(P? C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R₂P(X)? C?C? H and R₂P(X)? C?C? CH₃ (X ? oxygen, lone pair and R ? C₆H₅, N(CH₃)₂, OC₂H₅, N(C₆H₅)₂, Cl) from ¹H and ¹³C NMR spectra. In P^IV derivatives the following signs are obtained: ¹J(P? C)+, ²J(P? C)+, ³J(P? C)+, ³J(P? H)+, ⁴J(P? H)? . Linear relations are observed between ¹J(P? C), ²J(P? C) and ³J(P? C) versus ³J(P? H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for ¹J(P? C) and ²J(P? C). In P^III derivatives these signs are: ¹J(P? C)- and +, ²J(P? C)+, ³J(P? C)-, ³J(P? H)-, ⁴J(P? H)+. Only ³J(P? C) and ³J(P? H) reflect a small contribution of the Fermi contact term while in ¹J(P? C) and ²J(P? C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.     

Stereochemistry of alkyl 3-substituted 4-halotetrahydro-2-oxo-3-furancarboxylates: 2—1H and 13C NMR spectra

The ¹H NMR parameters of methyl 3-substituted cis-4-halotetrahydro-2-oxo-3-furancarboxylates are reported, with assignments of the ring protons based on solvent-induced changes in the vicinal trans coupling constants, ³J(H-4, H-5). Preferred conformations, ce with a pseudo-equatorial halogen for the cis isomers and ta with a pseudo-axial halogen for the trans isomers, have been suggested on comparison of the magnitudes of J(trans) and J(gem) in both series. The ³J(¹³CH₃, H-4) values measured for methyl cis-4-bromotetrahydro-3-methyl-3-furancarboxylate, methyl trans-4-bromotetrahydro-3-methyl-3-furancarboxylate and trans-3,4-dibromodihydro-3-methyl-2(3H)-furanone have confirmed the stereochemical assignments.     

1H and 31P NMR studies of rotational isomerism in phosphorus analogues of aspartic acid, 3-amino-3-phosphonatopropionic and 3-amino-3-(methylphosphinato) propionic acids

By the use of the ¹H? ¹H and ¹H? ³¹P coupling constants in two analogues of aspartic acid i.e. 3-amino-3-phosphonatopropionic and 3-amino-3-(methylphosphinato) propionic acids, it was shown that the six parameter formulation for the evaluation of mole fractions of three staggered ethanic rotamers is not necessarily better than the two parameter formulation in this system. The results allowed the recommendation of the following values for the two vicinal proton parameters i.e. J(HH)g=2.3, J(HH)t=13.9 and for the two vicinal proton-phosphorus parameters i.e. J(HP)g=4.2, J(HP)t=33.0 Hz.     

Trans‐Hydrogen‐Bond Scalar Couplings as a Source of Structural Constraints in NMR of Proteins: DFT Analysis

The conformational dependences of ¹⁵N,¹⁵N and ¹H,¹⁵N trans‐H‐bond spin‐spin scalar couplings, ^h2J(N,N) and ^h1J(N,H), have been investigated by sum‐over‐states density‐functional‐perturbation theory. The distance and angular dependence of the ^h2J(N,N) and ^h1J(N,H) coupling constants in the H‐bonded arrangement between acetylethylamine and imidazole molecules were examined for a wide range of mutual orientations. These molecules were used to model a structurally important H‐bond between the amide backbone of Arg7 and the remote imidazole side chain of His106 in the 44 kDa trimeric enzyme chorismate mutase from Bacillus subtilis. The magnitude of ^h1J(N,H) is relatively insensitive to the sampled rotations around three orthogonal axes centered on the tertiary N‐atom of the imidazole, whereas values of ^h2J(N,N) demonstrated a strong dependence on the value of the cone angle θ aligned with the amide group involved in the H‐bond. Simple functional approximations have been generated, enabling back calculations of the N⋅⋅⋅N distance and angle θ of the H‐bond, provided that the experimental values of both ^h2J(N,N) and ^h1J(N,H) coupling constants are available.     

Carbon-13 NMR studies of monohydroxylated and monochlorinated derivatives of Z- and E-p-menthanes

J(¹³C¹H) coupling constants for some methyl- and aminopyrimidines have been determined by ¹³C NMR. Both the one-bond and long-bond and long-range coupling constants follow general trends which can be summarized in a few simple rules. In particular, the ³J(C-i,H) coupling constants between a ring carbon C-i and the ring protons are larger than the ²J(C-i,H) coupling constants. The opposite is observed for the couplings between the ring carbons and the methyl protons: ³J(C,Me). These general rules are very useful for the assignment of resonances in complex ¹³C spectra of pyrimidines and seem to be valid for other 6-membered aromatic nitrogen heterocycles. Furthermore, the additivity of substituent effects on ¹J (CH) for monosubstituted pyrimidines allows the estimation of ¹J (CH) for polysubstituted pyrimidines with a very good accuracy.     

Nuclear magnetic resonance spectroscopy. Analysis of the 1H and 13C spectra of Br13CH213CH2Br

The ¹H and ¹³C NMR spectra of 1,2-dibromoethane-¹³C₂ have been analyzed to determine the magnitude (38·9 Hz) and sign (positive) of ¹J(C? C) relative to those of ³J(H? H) (positive). This type of coupling appears to be rather insensitive to the presence of bromine or methyl as substituents on the carbons.     

Unexpected behavior of the 3JCH coupling constant in unsaturated compounds

The experimental and theoretical behavior of the (OC) CC H ³J_CH coupling constant is investigated for a series of α,β-unsaturated compounds ( 1 to 8 ), and for some of them, the well-known relationship (³J_CHcis < ³J_CHtrans) was observed. However, for some compounds, close values for ³J_CHcis and ³J_CHtrans couplings were observed, and for aldehydes group containing compounds ( 7 and 8 E), an inversion order is observed (³J_CHcis > ³J_CHtrans). In all cases where the ³J_CHcis < ³J_CHtrans relationship it is not followed, a polar group or electronegative atom oriented in opposite direction (s-trans) to the H CC hydrogen is present, suggesting that conformational preference of such polar group or atoms are important factor on the behavior of ³J_CH couplings. Taking all of these in consideration, a new Karplus-type equation was proposed for ³J_CH couplings in α,β-unsaturated compounds, which can be used for configurational and conformational assignment on trisubstituted double bond derivatives.     

C3(SINGLE BOND)Mα Bond contribution to polarizability tensor and 3J(C1Mα) NMR coupling constant in 1-X-3-M-bicyclo[1.1.1]pentanes

In the present work, the relationship between the large substituent effects on ³J(C₁H) in 1-X-3-M-bicyclo[1.1.1]pentanes, I , and the polarizability of the bridgehead C₃(SINGLE BOND)M_α bond is investigated. The existence of such a relationship is suggested by the finding that the effect of an electronegative substituent X on ³J(C₁M_α) couplings in I (M=H) is due to a distortion of the C₃(SINGLE BOND)H bond toward the C₁ center, which enhances the Fermi contact interaction. If such distortion originates in an electrostatic effect, then in other members of this series it can be expected that the substituent effects on ³J(C₁M_α) couplings should depend strongly on the C₃(SINGLE BOND)M_α bond polarizability. Two approaches are followed. First, the ab initio CLOPPA-IPPP method is applied to study the C₃(SINGLE BOND)M_α bond contribution to the molecular static polarizability tensor in I (M=H, F, CH₃). Such bond polarizabilities are found to follow the same trend as calculated as well as experimentally determined substituent effects on ³J(C₁M_α) couplings, which were measured as part of this work in I [X=H, Cl; M=F, CH₃ and X=OCH₃; M=Sn(CH₃)₃]. Second, ³J(C₁M_α) couplings (M=H, CH₃) are calculated at an ab initio level for X=H, F, and they are compared with those obtained in the parent compound (X=H) if the calculation is carried out in the presence of an inhomogeneous electric field. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 181–188, 1998     

Proton n.m.r. spin-tickling studies of 13C-labeled compounds. The correlation of J(C,H) and J(H,H)

A tabulation has been compiled for twenty ¹³C? H coupling constants of various carboxylic acids and includes ²J(C,H), ³J(C,H) and ⁴J(C,H) values of olefins (both cis and trans); ³J(C,H), ⁴J(C,H) and ⁵J(C,H) values of aromatics; ³J(C,H) and ⁴J(C,H) values of acetylenes; and ²J(C,H) and ³J(C,H) values of rigid aliphatics. This tabulation has been completed in the present study by the spin-tickling proton n.m.r. study of ¹³C-carboxyl-endo-1,2,3,4,7,7-hexachloronorbornene-5-carboxylic acid, which has established that the ²J(C,H) value is negative and the ³J(C,H) values (both cis and trans) are positive in this system. A plot of these twenty J(C,H) values vs the corresponding J(H,H) values of geometrically equivalent model systems (where there is a proton in place of a carboxyl group) gives a correlation coefficient of 0·975 (with a slope of 0·62), indicating that carbon–proton and proton–proton couplings operate by similar mechanisms throughout this broad series of structural types.     

Nitrogen-15 coupling constants: Geminal coupling, 2J(15NH), in cis- and trans-aldonitrones and vicinal coupling, 3J(15NH), in cis-and trans-ketimines,oxaziridines and nitrones

Nitrogen-15-hydrogen ²J(¹⁵NH), ¹⁵N, ¹³C ¹J(¹⁵N¹³C) and ¹³C, H ¹J(¹³CH) coupling constants have been measured and their signs determined for cis-and trans-[9-anthryl(¹³C)methylene](²H₃)methylamine (¹⁵N)-oxide. Values of ²J(¹⁵NH) were of similar magnitude (～2 Hz) but were of opposite sign. The results are compared and contrasted with those reported for related imino and quaternary imino systems. Vicinal ³J(¹⁵NH) coupling constants have been measured in cis- and trans-¹⁵N-[1-(α-naphthyl)ethylidene]benzylamine and ¹⁵N-[1-(p-nitrophenyl)ethylidene]-t-butylamine and were found to be larger when the imino methyl group was cis to the nitrogen lone pair. The corresponding cis and trans ketonitrones formed by photoisomerization of the derived oxaziridines had ³J(¹⁵NH) values of c. 3.3 Hz. A study of the signs and magnitudes of observed and calculated ¹⁵N,H coupling constants for all of the ¹⁵N labelled imines, oxaziridines, imine N-oxides (nitrones) and similar model systems which were synthesized is described.     

187Os subspectra in 1H and 31P{1H} spectra of triosmium carbonyl clusters

A survey of the use of ¹⁸⁷Os satellite subspectra in ¹H and ³¹P{¹H} spectra of triosmium carbonyl clusters is reported. By varying evolution delays in HMQC spectra of [Os₃(µ‐H)₂(CO)₁₀] we have selectively extracted the values for ¹J(Os,H) and ²J(Os,H), respectively. An analysis of the principal modes of phosphine coordination in triosmium clusters demonstrates that ³¹P{¹H}¹⁸⁷Os satellite subspectra are diagnostic for equatorial coordination [¹J(Os,P) = 211–223 Hz] or for axial coordination (perpendicular to the plane of the cluster) [¹J(Os,P) ≈ 147 Hz]. Chelating and bridging diphosphines yield ¹⁸⁷Os satellite subspectra which are the sum of A₂X and AA′X spin systems. If significant P–P coupling is present, the AA′X component requires simulation. All observed ²J(Os,P) trans‐equatorial couplings fall in the range 38–65 Hz. Copyright © 2001 John Wiley & Sons, Ltd.     

1H- und 13C-NMR-Untersuchungen zur Struktur N-substituierter Tetrazole—Die Strukturen des N-Methoxycarbonyl-, N-Acetyl- und N-(Tri-n-butylstannyl)-tetrazols sowie Substituenteneffekte auf δ13C und 1J(CH)

The ¹H and ¹³C NMR spectra of several isomeric N-substituted tetrazoles have been investigated. ¹³C NMR is shown to be more useful for distinguishing between structural isomers of N-substituted tetrazoles except for those carrying electropositive substituents like SnBu₃. Correlations of δC-5 (inverse) and ¹J(C-5,H) with s?₁ found for 1-substituted tetrazole allowed the identification of the N SnBu₃ derivative as 1-(tri-n-butylstannyl)tetrazole. The phenyl carbon chemical shift difference ΔC′ = δC-3′-δC-2′ is insignificant for structure elucidation and conformational studies of N-substituted 5-phenyltetrazoles; ΔH′ from ¹H NMR spectra seems to be more useful.     

1H-NMR.-spektroskopische Analyse von prochiralen Allencarbonsäureestern mit optisch aktiven Europium-Verschiebungsreagenzien

¹H-NMR. Spectroscopic Analysis of Prochiral Allenic Esters Using Optically Active Europium Shift Reagents The prochiral allenic methyl esters 1–4 (cf. Scheme) show in the presence of 1 mol-equiv. tris[3-(heptafluorobutyryl)-(+)-camphorato]europium (III) (Eu (hfc)₃) in 1,1,2-trichloro-1,2,2-trifluoroethane (TCFE) induced unlike ¹H-NMR. shift differences (ΔΔδ) for the enantiotopic protons and methyl groups on C(4), respectively (cf. Fig. 2 and 3). This effect allows to determine directly the ²J_H,H coupling constants of the geminal protons on C(4) of the allenic esters 1 (15.5 Hz) and 2 (14.5 Hz) (cf. Table 2).     

On the Karplus relation for 3J(POCC) of nucleotides

The original Karplus parameters for analysing ³J(POCC) magnitudes of nucleotides in terms of conformational properties of the O? C bond were taken from results for 3′,5′-nucleotides and applied to 3′→ 5′-oligonucleotides; the parameters were later modified to take account of ‘largey’ magnitudes of ³J(POCC) observed in 2′ → 5′-oligonucleotides. In this work the origin of this discrepancy is explained in terms of substituent electronegativity effects at C-1′, and quantified using the ¹³C NMR results of 2′,3′-cyclic mononucleotides. A new set of Karplus parameters suitable for analysing ³J(POCC) magnitudes in 3′- and 5′-nucleotides and 3′ → 5′-oligonucleotides is determined from ¹³C NMR measurements on 3′-nucleotides and available results for 3′,5′-cyclic mononucleotides. A method of dealing with J(P, C-1′) coupling in 2′-nucleotides, 2′,3′-cyclic nucleotides and 2′ → 5′-oligonucleotides using the same Karplus relationship is suggested.     

Fluoro-α-amino acids. 1—use of 19F NMR spectroscopy for the configurational determination of β-fluoro-α-amino acids through complexation by 18-crown-6 ether

Erythro and threo configurational assignments have been made for 11 β-fluoro-α-amino acids or esters using the effect of complexation of the ammonium group by 18-crown-6 ether on the ¹⁹F NMR parameters. For the erythro configurations, ³J(HF) increases and a high-field ¹⁹F chemical shift is generally observed; these phenomena are accompanied by a decrease in ³J(HH) and ³J(CF). The opposite effects are observed for the threo configurations. These observations can be explained by a change in the relative population of the conformers around the Cα-Cβ bond on complexation of the ammonium group. This complexation impairs the interactions between the ammonium and fluorine groups and, concomitantly, the steric hindrance between the ammonium and R (methyl, phenyl or carboxylate) groups is increased.