bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural effects on 17O NMR shifts of cyclic phosphine oxides
Authors: Quin Louis D. , Szewczyk Jerzy , Linehan Kathleen , Harris David L.
Published: May 2005

The 17O NMR chemical shifts of a variety of cyclic phosphine oxides were recorded at natural abundance. The shifts proved to be extremely sensitive to structural effects such as ring size and the presence of γ‐interactions. Values were found to cover a 70 ppm range. The most unusual effect was discovered with phosphine oxide groups in the 7‐position of the norbornene framework. When the oxygen was anti to the double bond, exceptionally strong deshielding (by as much as 60 ppm) occurred relative to the isomer with syn oxygen. 17O NMR clearly has value as a structural diagnostic technique with phosphine oxides.
Carbon‐13 NMR spectra of substituted 2‐thiophenecarboxanilides
Authors: Amato Maria E. , Fisichella Salvatore , Musumarra Giuseppe , Bottino Francesco A.
Published: May 2005

Carbon‐13 NMR shifts for substituted 2‐thiophenecarboxanilides of general formula XC4H2SCONHC6H4Y(X=5‐OMe, 5‐Me, H, 5‐Br, 5‐NO2; Y=H, p‐OMe, pMe, p‐NO2, m‐Me, m‐Cl, m‐NO2) in DMSO‐d6 solutions are reported.

The effects of the X and Y substituents on these shifts are discussed, and correlated with substituent constants and with carbon shifts of analogous series of compounds.
Correlation of 1H and 13C NMR spectra by selective inverse INEPT. Assignment of the proton and carbon spectra of methyl (5R*, 6S*,8Z,11Z,14Z)‐5,6‐epoxyeicosa‐8,11,14‐ trienoate
Authors: Crossley Maxwell J. , Field Leslie D. , Gosper Jeffrey J. , Messerle Barbara A.
Published: May 2005

Selective inverse INEPT and 13C → 1H → 1H heteronuclear relayed coherence transfer pulse sequences were employed to assign and correlate the proton and carbon NMR spectra of methyl (5R*,6S*,8Z,11 Z,14Z)‐5,6‐epoxyeicosa 8,11,14‐trienoate. The transfer of coherence from specific carbon nuclei in the molecule to protons was employed as a one‐dimensional method to correlate carbon and proton resonances. The one‐dimensional C→H coherence transfer experiments are particularly useful for C‐H correlation in situations where only a small amount of sample is available and two‐dimensional methods are only marginally applicable or impractical.
Sign determination of the two‐bond 15N‐15N spin‐spin coupling constant of a pyrimidine ring by a selective 15N decoupling technique
Authors: Kuroda Yoshihiro , Fujiwara Yasuhiro
Published: May 2005

The sign 2J(NN) of 2‐chloro‐6‐methyl‐[15N2]pyrimidine has been determined by 1H‐{1H (selective)} and 13C‐{1H (noise), 15N (selective)} triple resonance techniques. The sign was proved to be negative (‐1.6 Hz); consequently, chlorine substitution at C‐2 was found to make 2J(NN) more negative, since the magnitude of 2J(NN) of [15N2] pyrimidine is nearly equal to zero. It is stressed that sign determination for the spin couplings between hetero‐nuclei is easier to perform when the resonance of one of the hetero‐nuclei is irradiated than when that due to a proton is irradiated.
Determination of the stereochemistry of disubstituted fluoroethylenes by 13C NMR spectroscopy
Authors: Bosch M. P. , Camps F. , Fabriàs G. , Guerrero A.
Published: May 2005

The stereochemistry of 1,2‐disubstituted fluoroethylenes, of general formula RSH2CHCFR′, has been ascertained from the different magnitudes of the upfield shift effect promoted by fluorine on the 13C NMR absorptions of the underlined γ‐carbon of the fluorinated analogue in comparison with those of the protonated parent compounds. Likewise, this assignment was also possible from the study of the values of the 2J(CF) and 3J(CF) coupling constants in the two isomers.
Compounds with bridgehead nitrogen. 51—The NMR spectra and stereochemistry of the 6‐ethylindolizidines
Authors: Banting Lee , Crabb Trevor A. , Trethewey Andrew N.
Published: May 2005

1H and 13C NMR spectroscopy showed that both isomers of 6‐ethylindolizidine adopt predominantly the trans‐fused conformation in CDCl3 at 298 K. ΔG for the cis‐⇌tram‐fused conformational equilibrium in indolizidine must accordingly be not less than 2.8 kcal mol−1.
Guidelines for the design of kinetic NOE experiments from computer simulation
Authors: Williamson M. P.
Published: May 2005

A FORTRAN computer program has been written that calculates the time course of NOEs in spin systems of arbitrary complexity. The program first calculates spin‐lattice and cross‐relaxation rates from the molecular parameters, and then calculates all NOEs simulataneously by a numerical integratio of the Solomon equations. This method is extremely fast and easy to program, and may be applied to calculation of truncated drive NOEs or transient NOEs. The program is applied to peptide and protein structures using various correlation times, in order to develop a picture of the behaviour of the NOE under various conditions. The results are used to suggest guidelines for the design of NOE experiments to ensure that the structural information is recovered in an efficient way, and that experiments are not misinterpreted. The distinction of α helix from 310 helix by NOEs is discussed.
Conformational analysis of the repeated sequence of glutelin‐2, a maize storage protein
Authors: Pons Miquel , Feliz Miguel , Celma Carles , Giralt Ernest
Published: May 2005

The presence of repeated proline‐rich sequences constitutes a common trend in several cereal storage proteins. The protected hexapeptide Boc‐Val‐His‐Leu‐Pro‐Pro‐Pro‐OH (1), with the sequence of the repeated region of glutelin‐2 (28 kD) from maize, has been studied by proton and 13C NMR in D2O, DMSO‐d6, CDCl3 and CDCl3‐CD3OD at different temperatures. Spectra were assigned mainly by using 2D correlation techniques. The spectra in D2O and DMSO‐d6 suggest that peptide 1 has a random coil, all‐trans conformation. In CDCl3 1 presents a folded conformation, stabilized by hydrogen bonds, with one of the methyl groups of the valine residue situated over the histidine ring. In CDCl3‐CD3OD 1 is present as a mixture of different conformations. The spectral data are discussed taking as a reference the known conformation of polyproline.
17O NMR studies of the effect of mixed ligands on the bound water in aqueous solutions of amino acids and Co(II)
Authors: Gotsis Efstathios D. , Fiat Daniel
Published: May 2005

The effect of mixed ligands on the lifetime and 17O hyperfine coupling constant of water bound to Co2+ in aqueous solutions of proline, glycine and alanine was determined, as a function of pH, by means of 17O NMR. The lifetime of the coordinated water molecules decreased from 4.9 X 10−7 s (for the pure aqueous complex) to 3.5 × 10−8 at pH 8, where more than one complex of proline were present. Smaller changes were measured for the 17O hyperfine coupling constant of water [from ‐ 1.7 × 107 Hz for Co(H2O) to ‐1.45 × 107 Hz measured at pH 6 in the presence of proline], and the enthalpy of activation of the first‐order exchange from the first coordination sphere of Co2+ (from 7.4 ± 0.2 kcal mol−1 for the pure aqueous complex to 6.2 ± 0.4 kcal mol−1 at pH 8 in the presence of proline).
Total assignment of the 1H and 13C NMR spectra of new 1‐phenyl‐ and 1‐cyano‐substituted 3,3‐dimethyl‐2‐thiatricyclo[3.2.1.16,8]nonane 2,2‐dioxide through the application of two‐dimensional NMR techniques
Authors: Faure Robert , Vacher Bernard , Samat André , Chanon Michel
Published: May 2005

Total assignment of 13C and 1H NMR spectra of the new compounds 1‐cyano‐ and 1‐phenyl‐substituted 3,3‐dimethyl‐2‐thiatricyclo[3.2.1.16,8]nonane 2,2‐dioxide was achieved using the concerted application of two‐dimensional homonuclear and heteronuclear chemical shift correlations. This unequivocal structure determination rules out the formation of a six‐membered ring during the intramolecular cyclization of the α‐sulphonyl‐C centred radical originating from 5‐endo‐isopropylsulphonyl‐5‐exo‐substituted norbornene.
An internal deuterium NMR thermometer
Authors: Roth Klaus
Published: May 2005

The temperature of an NMR sample can be indirectly determined by using a suitable deuteriated reference compound and the lock channel for observing the deuterium rapid‐passage NMR spectrum. By calculating the autocorrelation spectrum by two forward Fourier transformations, the relative chemical shift differences can easily be determined. The procedure can be performed on most commercial spectrometers and is completely independent of the frequency of the observed nucleus and/or any high‐power proton decoupling of the sample.
Carbon‐13 NMR studies of multicyclic lactams. Structures and 13C assignments by lanthanide induced shifts, relaxation studies and MINDO/3 calculations
Authors: Barfield Michael , Babaqi Abdulla S.
Published: May 2005

Carbon‐13 NMR studies were performed with a series of nineteen multicyclic lactams. The solution conformations of most of these were determined using the lanthanide induced shift (LIS) method in combination with x‐ray and/or MINDO/3 optimized geometries. These analyses show that E‐caprolactam and 3‐azabicyclo[4.3.1]decan‐4‐one have at least two conformations in solution. The LIS structural analyses were further confirmed by means of 13C T1 relaxation times with Gd(dpm)3 and Gd(fod)3 as relaxation reagents. However, relaxation data for carbons in proximity to the complexation site are not reliable for this purpose, probably because of the occurrence of mechanisms other than dipole‐dipole. It is also noted that it is better to compare carbons having the same number of bonded hydrogens. With the help of the LIS data it was possible to assign unambiguously the chemical shifts of the carbons in all of the lactams in this study.
29Si hyperfine splittings in the EPR spectra of silyl‐substituted alkyl and propynyl radicals
Authors: Walton John. N. C.
Published: May 2005

The 29Si satellites were observed in the EPR spectra of 3‐trimethylsilylprop‐2‐ynyl, 1‐trimethylsiloxyprop‐2‐ynyl and trimethylsiloxymethyl radicals. Comparison of the experimental a(29Si) values with spin densities calculated by semi‐empirical MO methods led to a value of 810 G for Qsi. The magnitude and postive temperature dependence of the a(29Si) values in the siloxy‐substitued radicals showed that their preferred conformations are staggered with the silicon atom in the nodal plane of the orbital containing the unpaired electron. This contrasts with the analogous β‐trialkylsilkylethyl radicals, which adopt eclipsed confromations. The rotaton barrier baout the C‐αO bond in trimethylsiloxymethyl radicals was estimated to be 3.8 keal mol−1. The preference of β‐oxamethyl radicals for the staggered conformation was attributed to the comparatively large stablization due to the interacton of the unpaired electron with the adjacent oxygen, and an attempt was made to quantify this effect.
Magnitude and sign of C,C coupling constants in acetylenes and allenes
Authors: Lambert JöRg , Klessinger Martin
Published: May 2005

One‐ and two‐bond C,C coupling constants and the signs of ten of the two‐bond coupling constants were determined from the INADEQUATE and SLAP spectra of four acetylenes and one allene. The geminal C,C coupling constants involving sp‐hybridized carbons are found to be positive and to correlate linearly with the corresponding s character products. In contrast, INDO‐SCPT calculations yield negative values for these coupling constants, and no correlation with the s character products. A separation of those parts of the coupling information transmitted by the σ and π electron framework, based on INDO‐FPT‐PRMO calculations, reveals some possible reasons for the poor performance of the INDO‐SCPT method for systems with π‐electrons.
A rare example of extremely strong carbon—carbon coupling: Analysis of 13C and 1H NMR spectra of a 13C2‐acetylenic ketone
Authors: Auchus Richard J. , d'Avignon André , Covey Douglas F.
Published: May 2005

NMR spectra are reported for an acetylenic ketone enriched with 13C in the acetylenic carbon atoms that exhibits extremely strong C‐C coupling. Chemical shifts and coupling constants have been extracted from computer simulations of the second‐order 1H and 13C spectra. The two acetylenic carbon atoms exhibit a Δ ν/J ratio of 0.2. Owing to the strong coupling, the double‐quantum coherence 13C spectrum requires an unusually long (58 ms) interpulse delay time in order to obtain a good spectrum. NMR spectra of this compound provide a unqiue example of strong coupling in a CCH (AB or ABX) spin system.
Effect of intramolecular and intermolecular exchange processes on the 1H NMR spectra of 2‐chloro‐1,3,2‐dioxarsolanes
Authors: Song S. K. , Watkins C. L. , Krannich L. K.
Published: May 2005

The 1H and 13C NMR spectra of solutions of 2‐chloro‐4,4,5,5‐tetramethyl‐1,3,2‐dioxarsolane (1) and 2‐chloro‐1,3,2‐dioxarsolane (2) are reported as a function of temperature, concentration and solvent. These data indicate rapid intramolecular conformational averaging for (1) and (2) under all the conditions investigated. Additionally, intermolecular conformational averaging processes are shown to be present. The kinetic parameters for intermolecular exchange were obtained from line shape analysis of the 1H NMR data. These results indicate the intermolecular exchange to be bimolecular in nature, involving a four‐centered transition state. The OCH2CH2–O torsional angle of (2) has been calculated from the analysis of its AA′BB′ 1H NMR spectral patterns, obtained at low concentrations in the absence of intermolecular exchange.
A 59Co NMR chemical shift and relaxation study of preferential solvation toward tris(acetylacetonato)cobalt(III)
Authors: Grahn Hans , Edlund Ulf , Holak Tadeusz A.
Published: May 2005

A 59Co NMR chemical shift and relaxation study of the preferential solvation of tris(acetylacetonato)cobalt(III) was undertaken by varying the solute concentration in cyclohexane. As expected, the preferred solvation is most pronounced for hydrogen‐bond donating solutes, such as chloroform and methanol. However, the expected levelling of the 59Co chemical shift curve on increasing the alcohol molar fraction is not observed because of competing solute‐solute interactions in bulk solution. The order of preference is close to that proposed using paramagnetically induced relaxation times or shifts in solutions doped with tris(acetylacetonato)chromium(III). The 59Co line‐width measurements correlate with Co(acac)3 rotational correlation times. Contrary to earlier proposals, the 59Co relaxation is claimed to be controlled by modulation of the static quadrupolar tensor of Co(acac)3.
Calculation of 2J(HH) and 1J(CH) for transition metal methyl compounds; evidence for geometric dependence of 2J(HH)
Authors: Green Jennifer C. , Payne Martin P.
Published: May 2005

Calculations of 2J(HH) and 1J(CH) for CH4, TiCl3CH3, Mn(CO)5CH3 and Zn(CH3)2 as a function of C‐H distance and MCH angle have been carried out, based on the extended Hückel method. The positive geminal coupling constant found for TiCl3CH3 is shown to be caused by the small TiCH angle, and the results suggest that the sign and magnitude of the geminal coupling constant in methyl groups could be a useful probe of their solution structure.
1H and 13C NMR spectra of derivatives of 2‐hydroxy‐3‐methylbut‐3‐enenitrile and 2‐hydroxy‐3‐methylbut‐2‐enenitrile
Authors: Jaroszewski Jerzy W. , Ettlinger Martin G.
Published: May 2005

A series of derivatives of 2‐hydroxy‐3‐methylbut‐2‐ and ‐3‐enenitrile, including β‐D‐glucopyranosides, were obtained and their 1H and 13CNMR spectra were investigated. The spectra were assigned using lanthanide‐induced shifts, NOE difference spectroscopy and deuterium labelling.
N‐methylene chemical shifts of N‐benzylpyridinium salts
Authors: Munavalli S. , Hsu F.‐L. , Szafraniec L. L. , Beaudry W. T. , Poziomek E. J.
Published: May 2005

The chemical shifts of N‐benzylpyridinium salts have been measured in D2O, and the substituent induced chemical shifts of the methylene protons are in substantial agreement with those expected from the overall electronic effects of the substituents. An additivity effect of the substituents on the methylene resonance is also observed.
1H NMR and a study of the anomalous temperature dependence of the 35Cl NQR frequencies in 2‐chloro‐3‐pyridinol
Authors: Raghoottama P. S. , Soundararajan S. , Ramakrishna J.
Published: May 2005

A 35Cl NQR study of 2‐chloro‐3‐pyridinol showed the presence of four NQR signals at 77 K. One of the lines showed a positive temperature coefficient of the NQR frequency. 1H NMR studies showed the presence of intramolecular hydrogen bonding, and the anomalous NQR temperature dependence has been explained in terms of Bayer and hydrogen bond effects. The room temperature x‐ray structure and the low‐temperature NQR data suggest the presence of a phase transition.
Comparison of four pulse sequences for the routine application of proton‐carbon shift correlation
Authors: Kessler H. , Griesinger C. , Zimmermann G.
Published: May 2005

Four different pulse sequences for proton‐carbon shift correlation via 1J(CH) couplings are compared using amacrolide as a practical example. These are the COLOC sequence, a new improved variant of COLOC, the 2D‐DEPT‐COSY sequence and its new constant‐time variant. It emerged that the 2D‐DEPT‐COSY and the modified COLOC sequences are the most appropriate for the purpose of routine proton‐carbon shift correlation via direct coupling.
Peptide—lanthanide cation equilibria in aqueous solution. III—Temperature dependence of l‐carnosine‐Ln3+ bound shifts. Isomorphous substitution and side‐chain folding
Authors: Mossoyan J. C. , Ouarzazi J. , Benlian D.
Published: May 2005

The temperature dependence of paramagnetic shifts induced for proton resonances has been investigated for lanthanide (Dy, Ho and Yb) complexes of L‐carnosine. Two different methods of data reduction were used to separate contact, pseudo‐contact and diamagnetic contributions to the paramagnetic shift, one using induced bound shifts and the other based on temperature plots of the induced shift ratios. These studies revealed that diamagnetic effects, which include conformational changes, inductive effects and direct field effects, cannot be neglected. In the Dy, Ho and Yb complexes the side‐chain is folded, but isomorphous replacement and axial symmetry are retained.
Stereostructure of cycloadducts of norbornane/ene‐fused dihydro‐1,3‐ and ‐3,1‐oxazines
Authors: Sohár P. , Stájer G. , Bernáth G.
Published: May 2005

The steric structures of the tetracyclic mono‐ and the pentacyclic bis‐adducts formed in the cycloadditions of norbornane‐ and norbornene‐fused 1,3‐ and 3,1‐dihydrooxazine dipolarophiles with diphenylnitrilimine or benzonitrile oxide were investigated. These reactions could yield 2–8 annellation and positional isomers. The structures of the products were proved by 1H and 13C NMR spectroseopy, and the various potentially stable conformations of the flexible hetero rings were evaluated. The assignments were confirmed by double resonance and DEPT measurements; the steric structures were supported by the results of DNOE experiments.
Carbon‐13 NMR shift data of some 3H‐1,4‐benzodiazepine‐2,5(1H, 4H)‐diones
Authors: Mohiuddin Ghulam , Reddy Padala Satyanarayana , Ratnam Chengalvala Venkata
Published: May 2005

Carbon‐13 chemical shifts of eight 3H‐1,4‐benzodiazepine‐2,5(1H, 4H)‐diones are reported. The carbonyl chemical shifts have diagnostic value for distinguishing these diones from the isomeric 1,3‐benzodiazepine‐2,5‐dione structures.
The tautomerism and stereochemistry of β‐sulphinyl enamines
Authors: Kozerski L. , Kawęcki R. , Bednarek E.
Published: May 2005

The tautomeric equilibrium of β‐sulphinyl enamines in solution and the stereochemistry of its components have been studied by 1H and 13C NMR. The parent aliphatic β‐sulphinyl enamines bearing secondary alkylamino residues exist in two tautomeric forms in chloroform solution; the Z‐enamine form always predominates over the E‐imine form. α‐Alkyl‐substituted tertiary compounds exist in solution as a 4:1 mixture of E and Z isomers. NOE enhancements were measured in the two groups of compounds to confirm the stereochemical conclusions derived from the chemical shift interpretation.
1H NMR spectra of pyranocoumarins
Authors: Manzini Paolo , Rodighiero Paolo , Pastorini Giovanni , Guiotto Adriano
Published: May 2005

The 1H NMR spectra of variously annulated pyranocoumarins are reported. The complete assignment of chemical shifts was achieved by using coupling constants and the shift effects induced by the introduction of methyl groups at various positions on the pyranocoumarin nucleus, and by comparison with the spectra of known compounds.
13C spin—lattice relaxation in all‐trans retinal: Effect of the chemical shift anisotropy
Authors: Pattaroni Christian , Lauterwein Jürgen
Published: May 2005

The 13C spin‐lattice relaxation times and nuclear Overhauser enhancement factors of all‐trans‐retinal were measured in acetone‐d6 at two different magnetic field strengths. The extent to which the chemical shift anisotropy mechanism was found to contribute to the relaxation rate of the quaternary olefinic carbons was between 23 and 37% at 4.70 T and between 48 and 66% at 8.45 T. Assuming anisotropic molecular motion and an asymmetric chemical shift tensor, the shielding anisotropies of carbons C‐5, C‐6, C‐9 and C‐13 were calculated to be 185, 172, 188 and 228 ppm, respectively. These are qualitatively similar to those obtained in a recent 13C NMR study of all‐trans‐retinal in the solid state. In contrast, the quaternary aliphatic carbon C‐1 was much less relaxed by the chemical shift anisotropy mechanism (contribution <11%). The relaxation of the proton‐bearing carbons was independent of the magnetic field and determined only by the dipole—dipole interaction mechanism.
Structural and NMR assignment study of the O‐linked glycopeptides of calf fetuin
Authors: Berman Elisha
Published: May 2005

Two O‐linked glycopeptides were isolated by protease digestion of calf fetuin. Using 13C and 1H NMR spectroscopy, it was established that both carry identical trisaccharide side‐chains, but they were found to possess different peptide moieties. Therefore, they must originate from different regions of the polypeptide backbone of fetuin. The two glycopeptides carry a total of three oligosaccharide chains, in accordance with previously published data. One glycopeptide was found to carry two side‐chains: one is linked to a serine and the other to a threonine that are separated by one alanine only. The other glycopeptide carries one sugar chain linked to a serine residue. It was not possible to isolate any glycopeptide which contained a second sialic acid residue directly linked to the N‐acetylgalactosamine, as reported earlier. Some long‐range chemical shift effects were observed in the NMR spectra of the glycopeptide, indicating a specific conformation for this glycopeptide as a result of the proximity of the two oligosaccharide side‐chains.
ENDOR spectra of vanadyl complexes in asphaltenes
Authors: Atherton Neil M. , Fairhurst Shirley A. , Hewson Geoffrey J.
Published: May 2005

It has been suggested, on the basis of electron spin resonance measurements, that the coordination of vanadyl complexed in asphaltenes is porphyrin‐like. We have examined a number of asphaltenes using electron nuclear double resonance (ENDOR) spectroscopy and obtained spectra from 14N and 1H nuclei. Comparison of the spectra with those of vanadyl octaethyl‐ and tetraphenyl‐porphyrins confirms that the porphyrin structure does indeed occur in the asphaltenes.
A 31 P NMR study of O,O′‐dialkyldithiophosphates: An unusual coupling
Authors: Ray G. Joseph , Caspari Gunter
Published: May 2005

A series of O,O′‐dialkyldithiophosphoric acids have been studied by 31P NMR, and a four‐bond 31P‐1H scalar coupling has been detected. This coupling is unusual because it is observed between phosphorus and only one of two available protons located on the same carbon, even when the alkyl fragment is simply an alkane that should not show any conformational preference. Variation of the structural features of the alkyl group showed that this coupling involved a “W” pathway.
Molecular conformations of dibucaine in solution as determined by NMR lanthanide—induced shifts and conformational energy calculations
Authors: Basti Mufeed , LaPlanche Laurine A. , Vanderkooi Garret
Published: May 2005

Proton lanthanide‐induced shifts (LIS) were measured for Yb(fod)3‐dibucaine complexes in CDCl3 solution. The data were used in conjunction with empirical energy calculations to determine the preferred conformations of dibucaine. The energy calculations and the LIS analysis were in agreement in showing that the plane of the amide group makes an angle of approximately 60° with the plane of the quinoline ring, and also that the two carbon‐carbon bonds between the amide group and the tertiary amine nitrogen are both in gauche configurations. Energy calculations showed that the diethyl tertiary zmine group has very restricted conformational freedom owing to internal steric constraints. The butyl ether group has considerable flexibility but is forced out of the plane of the quinoline ring by steric effects.
1H and 13C NMR conformational analysis in solution of isoproterenol a pure β‐agonist drug
Authors: Gaggelli Elena , Marchettini Nadia , Valensin Gianni
Published: May 2005

13C and 1H NMR parameters were measured for isoproterenol in solution. Spin‐lattice relaxation rates were considered and C‐H and H‐H J couplings were determined. The t rotamer was shown to occur in a much greater abundance than the two g rotamers. Dynamics in solution were interpreted in terms of a nearly isotropic motion of the α‐hydroxyphenethyl moiety and of a high degree of flexibility of the isopropyl moiety, Relevant distances and dipolar connectivities were measured and used to build up a Dreiding model of the most probable conformation.
A conformational investigation of zearalenone and the 6′‐zearalenols by carbon and proton NMR spectroscopy
Authors: Smith William B. , Watson William H.
Published: May 2005

The carbon and proton spectra for zearalenone and its two C‐6′ alcohol derivatives have been assigned using 2D techniques along with NOE difference spectra and the LIS of the dimethoxy derivative of the β‐alcohol. Low temperature and relaxation time studies on the latter compound support the existence of only one solution conformer for each molecule. Molecular mechanics calculations for each molecule predict the existence of several low energy conformers which differ in energy by less than 3 kcal/mol; however, barriers to conformational interchange could not be estimated. Partial analysis of the proton spectra allows a comparison of the NMR parameters with the MM derived conformations and with x‐ray structural data. The solution conformations of zearalenone and α‐zearalenol are closely related to the solid state conformations.
Acyclic stereochemical analysis by NMR spectroscopy
Authors: Kleinpeter E. , Meusinger R. , Duschek Ch. , Borsdorf R.
Published: May 2005

The diastereomers of a series of substituted γ‐chloropropyl methyl ethers with up to three chiral centres have been assigned by 1H/13C NMR spectroscopy from vicinal H,H coupling constants and the steric compression within the carbon skeleton (γ‐gauche effect). The necessary conformational study was carried out with the help of theoretically estimated steric 1,3‐parallel interaction energies.
Some observations on the WATR method for water suppression at 80 MHz
Authors: Dickinson Noel A. , Lythgoe Ronald E. , Waigh Roger D.
Published: May 2005

The WATR method for water suppression in 1H NMR spectroscopy has been evaluated at 80 MHz, using both ammonium and guanidinium chloride, with and without the addition of buffer salts. The pH of maximum effect has been found to depend on field strength and to be markedly affected by buffer salts, particularly phosphates. Provided that the pH is carefully controlled the method is simple and effective.
Carbon‐13 NMR chemical shifts in substituted 4,4‐dimethyl‐2‐phenyl‐1,3‐oxazolines
Authors: Evers M. , Christiaens L. , Llabres G. , Baiwir M.
Published: May 2005

A 13C NMR study of twenty‐one 4,4‐dimethyl‐2‐phenyl‐1,3‐oxazolines has shown that the chemical shifts of the oxazoline moiety are insensitive towards substitution on the phenyl ring.
13C NMR assignments of the isoprenoid chain carbons of retinoids from empirical chemical shift differences
Authors: Hope K. D. , Robinson C. Y. , Vaezi M. F. , Brouillette W. J. , Muccio D. D.
Published: May 2005

13C NMR assignments have been made for a series of 36 α‐ and 3,4‐dehydroretinoids with different substituents (alcohol, ester, aldehyde and acid) and for their separated E and Z geometrical isomers. The assignments were made by using 2D heteronuclear‐correlated NMR experiments. From the chemical shift data of 24 systematically related retinoids, empirical chemical shift changes due to four polar end groups (alcohol, aldehyde, carboxylic acids and esters), three chain configurations (all‐E, 9Z and 13Z), and two ring substitutions (2,6,6‐trimethyl‐cyclohex‐2‐enyl and 2,6,6‐trimethylcyclohexa‐1,3‐dienyl) were determined. All trends were found to be independent of each other, except for the dependence of the chemical shift change of the 13Z‐isomers on the polar end groups. The chemical shift changes were used to predict the chemical shifts of other retinoids based on two different ring structures (2,6,6‐trimethylcyclohexenyl and 4‐methoxy‐2,3,6‐trimethylphenyl).
Increased NOEs for small molecules using mixed solvents
Authors: Fesik Stephen W. , Olejniczak Edward T.
Published: May 2005

A simple procedure is proposed for increasing the size of NOEs in NMR studies of small molecules. The method involves the use of a mixed solvent (Me2SO‐d6‐D2O) to increase the viscosity of the solution such that ωtc >1. The advantages of this solvent system and approach are compared with other approaches currently in use.
Carbon‐13 NMR line width and relaxation studies of tert‐butyl bromide and tert‐butyl cyanide
Authors: Aksnes D. W. , Ramstad K. , Björlykke O. P.
Published: May 2005

Proton and 13C line widths and 13C spin‐lattice relaxation times (T1) were measured over a wide temperature region in liquid and solid tert‐butyl bromide (1) and tert‐butyl cyanide (2). A striking feature of the proton and 13C NMR spectra of 1 is the abrupt line narrowing at the phase I → phase II transition point. In 2, however, the line width does not vary with temperature in phase I, indicating that the translational motion is too slow to affect the line width.

An analysis of spin‐lattice relaxation times in both the liquid and solid phases is reported. It is shown that 13C T1 measurements can distinguish between internal methyl group reorientation (C3 motion) and uniaxial molecular reorientation of tert‐butyl groups (C3′ motion) if these motions are independent and responsible for the T1 relaxation over a large part of the temperature region. The 13C spin‐lattice relaxation mechanism in the liquid and disordered phases of 1, and the liquid phase of 2, is governed by overall molecular tumbling with an activation energy of 8–11 kJ mol−1. The 13C T1 data show that the faster motion in the ordered phases of 1 and 2 is the C3′ reorientation with an activation energy of 15–18 kJ mol−1 while the slower motion is the C3 reorientation with an activation energy of ca 19 kJ mol−1.
1H and 13C resonance designation of antimycin A1 by two‐dimensional NMR spectroscopy
Authors: Abidi S. L. , Adams B. R.
Published: May 2005

Complete 1H and 13C resonance assignments of antimycin A1 were accomplished by two‐dimensional NMR techniques, viz. 1H homonuclear COSY correlation, heteronuclear 13C‐1H chemical shift correlation and long‐range heteronuclear 13C‐1H COLOC correlation. Antimycin A1 was found to consist of two isomeric components in a 2:1 ratio based on NMR spectroscopic evidence. The structure of the major component was newly assigned as the 8‐isopentanoic acid ester. The spectra of the minor component were consistent with the known structure of antimycin A1.
Differentiation of diastereomeric 2‐substituted cyclohexanamines with three chirality centres by 13C NMR spectroscopy
Authors: Knupp Gerd , Frahm August W.
Published: May 2005

The 13C NMR spectra of optically active primary and secondary 2‐substituted cyclohexanamines were measured and the chemical shifts were unequivocally assigned. Similar studies were made with four diastereomeric 2‐methyl‐N‐(1‐phenylethyl)cyclohexanamines with three chirality centres.
13C NMR chemical shift substituent effects. 5—α‐Monosubstituted N,N‐diethylacetamides
Authors: Rittner Roberto , Martins Marcos A. P. , Clar Günter
Published: May 2005

Carbon‐13 NMR chemical shifts of a series of α‐monosubstituted N,N‐diethylacetamides [YCH2C(O)NEt2, Y = Me, Cl, Br, I, OMe, SMe, and NMe2] are reported. The α‐methylene and carbonyl carbon chemical shifts are correlated with the Pauling electronegativities (Ep) and Charton's localized electrical parameters (σL), respectively. The non‐equivalence of the chemical shifts for the syn and anti‐N‐alkyl carbon atoms are attributed to the electric field and steric compression effects and also to the YCH2cis and trans‐γ‐effects.
Nuclear magnetic resonance and infrared spectral characterization of some peroxysterols
Authors: Jaworski Krzysztof , Smith Leland L.
Published: May 2005

Proton and infrared absorption spectra of seven peroxysterols of general structure 6ξ‐alkoxy‐5,6ξ‐epidioxy‐5ξ‐5,6‐secocholestane‐3β,5‐diol reveal low‐field (δH 10.0–10.8) sharp one‐proton singlets and associated sharp 3280–3330 cm−1 absorption bands of the 5ξ‐hydroxy group, intramolecularly hydrogen bonded to vicinal peroxide oxygen in a previously unrecognized correlation. The peroxysterols are also characterized by 13C NMR spectra.
Carbon‐13 NMR spectra of 1,3‐dioxolanes. II—determination of α, β and γ parameters for 2‐ and 4‐methyl groups in stereoisomeric derivatives by the pattern molecule method
Authors: Espinosa Antonio , Gallo Miguel A. , Campos Joaquín , Entrena Antonio , Camacho Encarnación
Published: May 2005

On the basis of the stereochemistry of the 1,3‐dioxolane ring, the molecular pattern method allows the establishment of α, β and γ parameters for the 2‐Me and 4‐Me substituents. Values of α, β and γ additive parameters for the syn and anti 4‐Me group in 2,2,4‐trisubstituted‐1,3‐dioxolanes are proposed. The average values of the α, β and γ effects for the 2‐Me and 4‐Me groups obtained by the molecular pattern method are consistent with those reported from a multiple linear regression analysis.
Chiral hydroxymethyl groups: 1H NMR assignments of the prochiral C‐5′ protons of ribonucleosides
Authors: Kline Paul C. , Serianni Anthony S.
Published: May 2005

Adenosine, cytidine, guanosine and uridine were prepared with stereoselective deuteriation at C‐5′ and used to assign the prochiral C‐5′ protons in 300 MHz 1H NMR spectra. In all cases, the more shielded C‐5′ proton was found to be the pro‐R proton. From these assignments, C‐4′C‐5′ rotamer populations have been estimated, and some discussion of the errors associated with these calculations is given. The relative populations of rotamers in ribonucleosides were found to be affected by structure at C‐1, ring conformation and possibly solution pH.
1H NMR spectra of aflatoxin‐B2 and aflatoxin‐G2
Authors: Blunden Gerald , Gordon Sally M. , Jazwinski Mary J. , Roch Olive G. , Crabb Trevor A. , Jewers Kenneth , Coker Raymond D.
Published: May 2005

The 1H NMR spectra of 2,3,6a,8,9,9a‐hexahydro‐4‐methoxycyclopenta(c)furo[3′,2′:4,5]furo[2,3‐h][l]benzopyran‐1,11‐dione (aflatoxin‐B2) and 3,4,7a,10a,9,10,10a‐hexahydro‐5‐methoxy‐1H,12H‐furo[3′,2′:4,5] furo[2,3‐h]pyrano[3,4‐c][l]benzopyran‐1,12‐dione (aflatoxin‐G2), including aromatic solvent‐induced shifts, are described and the solution conformation of the tetrahydrofuran moieties is discussed.
Suppression of direct peaks in two‐dimensional heteronuclear NOE spectra. Sensitivity‐enhanced detection of weak indirect and relay peaks
Authors: Kövér Katalin E. , Batta Gy.
Published: May 2005

A spin–echo sequence is proposed for the suppression of the generally unnecessary strong direct cross‐peaks in two‐dimensional heteronuclear NOE and relayed incoherent transfer spectroscopy. The procedure also increases the intensity of “remote peaks,” thereby enhancing the sensitivity of these techniques.
Polar substituent effects in the bicyclo[2.2.2]octane ring system: A 19F NMR study of some 4‐substituted bicyclo[2.2.2]octane‐1‐carbonyl fluorides
Authors: Adcock William , Iyer V. Sankar
Published: May 2005

Fluorine‐19 substituent chemical shifts (SCS) are reported for a series of 4‐substituted bicyclo[2.2.2]octane‐1‐carbonyl fluorides containing a limited but a representative number of dipolar substituents. The 19F SCS, which cover a very narrow range (<0.5 ppm), are found to correlate poorly against polar field parameters (σF). Polar field susceptibility parameters (ρF) for the fluorine probe were determined indirectly and their origin is briefly discussed in the light of the carbonyl 13C SCS which reflect π polarization of the COF group.
Application of relayed coherence transfer two‐dimensional nuclear magnetic resonance spectroscopy to the assignment of 1H chemical shifts in steroids
Authors: Hughes Donald W.
Published: May 2005

Relayed coherence transfer (RELAY) two‐dimensional NMR spectroscopy was demonstrated to be an effective technique for overcoming the problem of overlapping multiplets in the analysis of the 1H NMR spectra of steroids. Cross‐sections through appropriate proton resonances resulted in resolved spectra of the spin systems for each of the saturated rings of the estrogenic hormones 17β‐ and 17α‐estradiol. During RELAY experiments with a fixed delay time of 0.042 s it was possible to observe RELAY cross‐peaks between H‐11α and 18‐CH3 which resulted from magnetization transfer via long‐range coupling between 18‐CH3 and H‐12α. The difference in stereochemistry at C‐17 of these estradiol epimers allowed an examination of the effect of substituent configuration on the RELAY cross‐peak intensity in order to determine the ability of the RELAY method to provide qualitative structural information.
Study of intramolecular hydrogen bonding in o‐anisic acid and o‐anisamide by 17O NMR and Ab initio MO calculations
Authors: Jaccard Guy , Carrupt Pierre‐Alain , Lauterwein Jürgen
Published: May 2005

The 17O chemical shifts of the methoxy groups of o‐anisic acid (1) and o‐anisamide (2) were measured in various solvents at 40°C. The methoxy resonances were displaced to low frequency in CDCl3 relative to CD3CN and CD3OD solutions. This shielding can be attributed to intramolecular hydrogen bonding in the non‐polar solvent. The percentage of hydrogen bonding was determined by 1H NMR spectroscopy. The hydrogen bond‐induced 17O chemical shifts of the methoxy groups were evaluated as ‐−10 and −3 ppm in 1 and 2, respectively. Their sensitivity to hydrogen bonding is therefore much smaller than that of carbonyl groups. Ab initio calculations at the STO‐3G level were used to determine the geometry of the hydrogen bonds and their influence on the total energy of the molecules. The intramolecular hydrogen bond energy of 1 was evaluated as 2.18 kcal mol−1. Hydrogen bonding in 1 and 2 resulted in an increase in both the σ‐ and π‐electron densities at the methoxy oxygen atoms. Arguments are presented which show that the variation in atomic charges is the principal origin of the low‐frequency 17O chemical shifts.
NMR assignments for some 2‐substituted 2,6,6‐trimethyl‐7‐oxabicyclo[3.2.1]octanes (dihydropinols)
Authors: Carman Raymond M. , Fletcher Mary T. , Lambert Lynette K.
Published: May 2005

1H and 13C NMR assignments for five 2‐substituted dihydropinols are reported.
Analysis of 13C, 14N residual dipolar coupling in the 13C CP/MAS NMR spectra of ribonucleosides
Authors: Olivieri Alejandro C. , Frydman Lucio , Grasselli Mariano , Diaz Luis E.
Published: May 2005

13C CP/MAS NMR spectra of nitrogen‐containing compounds often show complex signals when recorded at low field strengths. This effect is due to the 13C, 14N residual dipolar coupling which is not averaged to zero by magic‐angle spinning. Solid‐state 13C NMR spectra at 25 MHz of ribonucleosides are analysed on the basis of the isotropic chemical shifts measured at 50 MHz, together with the asymmetric splittings caused by the presence of 14N calculated using a first‐order equation. X‐ray diffraction and NQR data, together with several assumptions regarding the quadrupole tensor at each 14N site, are used to obtain a successful spectral simulation.
Structural and conformational analysis by 1H NMR and 13C NMR of a new angiotensin I converting enzyme inhibitor, the tert‐butylamine salt of (2S)‐2‐[(1S)‐1‐carbethoxybutylamino]‐1‐oxopropyl‐(2S, 3aS, 7aS) perhydroindole‐2‐carboxylic acid (perindopril)
Authors: Platzer N. , Bouchet J. P. , Volland J. P.
Published: May 2005

Perindopril, a potent inhibitor of angiotensin I converting enzyme, was studied by 1H NMR and 13C NMR in various solvents and at various temperatures. The cis and trans conformations of the amide bond were assigned. The conformations of the perhydroindole skeleton rings were studied by 1H NMR.
NMR spectra and stereochemistry of perhydrooxazolo[3,4‐a]pyridines
Authors: Crabb Trevor A. , Trethewey Andrew N. , Takeuchi Yoshito
Published: May 2005

Low‐temperature 13C and 1H NMR spectra show perhydrooxazolo[3,4]‐apyridine to exist in CDCl3CFCl3 solution at 183 K as an equilibrium between 73% trans‐fused and 27% O‐inside cis‐fused conformers. cis‐(H‐1, H‐8a)‐1‐Alkylperhydrooxazolo‐[3,4‐a]pyridines (alkyl = methyl, ethyl, isopropyl) adopt equilibria heavily biased towards the trans‐fused conformers, whereas the epimers adopt 18% O‐inside cis‐fused = 82% trans‐fused comformational equilibria at 183 K in CDCl3CFCl3. At 190 K in CDCl3 cis‐(H‐6, H‐8a)‐6‐ethylperhydrooxazolo[3,4‐a]pyridine adopts an equilibrium containing ca 3% trans‐fused conformer in equilibrium with 97% O‐inside cis‐fused conformer.
13C NMR chemical shift assignments for some carbazole derivatives
Authors: Katritzky Alan R. , Rewcastle Gordon W. , De Miguel Luis M. Vazquez , Wang Zuoquan
Published: May 2005

13C NMR chemical shift assignments have been made for a series of 1‐substituted carbazoles, 8‐substituted 1,2,3,4‐tetra‐hydrocarbazoles, 1‐substituted benzo[a]carbazoles and 6‐substituted dibenzo‐[c,g]carbazoles. Single examples were examined of other classes of substituted carbazoles: 3‐butylcarbazole and its tetrahydro precursor 6‐butyl‐1,2,3,4‐tetra‐hydrocarbazole, 8‐butyl‐ and 8,10‐diethylbenzo[a]carbazoles and their 5,6‐dihydro precursors, dibenzo[a,i]carbazole and its 5,6,7,8‐tetrahydro precursor, benzo[c]carbazole and its 6‐chloro derivatives and 5,6‐dihydrobenzo[c]carbazole and 5,6,8,9‐tetrahydrodibenzo[c,g]carbazole and their N‐methyl derivatives. In addition, the N‐(1‐pyrrolidinomethyl) derivatives of carbazole, 1,2,3,4‐tetrahydrocarbazole, benzo[c]carbazole and dibenzo[c,g] carbazole were also studied.
129Xe line widths in block copolymers
Authors: Brownstein Sydney K. , Roovers J. E. L. , Worsfold D. J.
Published: May 2005

Separate 129Xe lines are observed for Xe gas dissolved in the different regions of polystyrene–polyisoprene block copolymers. The variation in line width with copolymer molecular weight may be explained by diffusion between the two different phases.
Conformations of cycloalkenyl radicals: A dynamic EPR study of the cyclohept‐4‐enyl radical
Authors: Walton John C.
Published: May 2005

Cyclopent‐3‐enyl, cyclohex‐3‐enyl and cyclohept‐4‐enyl radicals were generated and their EPR spectra obtained in solution over a range of temperatures. The spectral data were consistent with a fully planar conformation for cyclopent‐3‐enyl radicals and a slightly flattened half‐chair conformation for cyclohex‐3‐enyl radicals. Cyclohept‐4‐enyl radicals showed exchange broadening in their EPR spectra which indicated inversion from one chair conformer to another with an Arrhenius activation barrier of 16.5 ± 0.3 kJ mol‐1.
1H and 13C NMR assignment of maltitol by a combination of 2D NMR and H/D isotope effects on nuclear shielding
Authors: Hoffman R. E. , Davies D. B.
Published: May 2005

Maltitol was assigned unequivocally without any need for reference to model compounds by a combination of 2D, SIMPLE (secondary isotope multiplets of partially labelled entities) and DIS (differential isotope shift) NMR techniques. The combination of these three techniques is very powerful for the assignment of molecules with many exchangeable hydrogen atoms, such as carbohydrates. In the case of maltitol a complete 13C NMR assignment was achieved in three solvents [H2O, D2O and (CD3)2SO] using three experiments. A 1H‐13C 2D correlation experiment allowed the 1H NMR spectrum to be assigned unequivocally for the first time.
13C and 31P NMR data for some 6‐aryloxydibenzo[d, f][1,3,2] dioxaphosphepin 6‐oxides/sulphides and 3‐cyclohexyl‐6‐(1, 1‐dimethylethyl)‐3, 4‐dihydro‐2‐aryloxy‐2h‐1,3,2‐benz‐oxazaphosphorine 2‐oxides
Authors: Naidu M. S. R. , Raju C. Naga
Published: May 2005

13C And 31P NMR chemical shifts and 13C31P coupling constants of 26 6‐aryloxydibenzo [d, f][1,3,2] dioxaphosphepin 6‐oxides/sulphides and 3‐cyclohexyl‐6‐(1, 1‐dimethylethyl)‐3, 4‐dihydro‐2‐aryloxy‐2H‐1,3,2‐benzoxazaphosphorine 2‐oxides are reported. The assignments are supported by SFORD spectra.
A revised 13C NMR spectral assignment of hellebrigenin
Authors: Van Heerden Fanie R. , Vleggaar Robert
Published: May 2005

The previously accepted 13C spectral assignment of hellebrigenin was re‐examined and revised signal assignments are proposed for C‐1, C‐7 and C‐11. Results obtained in a (1H, 1H) COSY experiment and NOE experiments enabled us to assign the 1H NMR spectrum of hellebrigenin. The 13C NMR spectrum was subsequently assigned unambiguously by the correlations observed in a 2D (13C, 1H) chemical shift correlation experiment and a COLOC experiment.
The effect of p—π conjugation on the barrier to pyramidal sulphur inversion in pentacarbonylchromium complexes of thioethers
Authors: Gryff‐Keller Adam , Szczeciński Przemysław , Koziel Hanna
Published: May 2005

Barriers to the pyramidal inversion of sulphur bonds were investigated for five pentacarbonylchromium complexes of cyclic and acyclic thioethers. The expected effects from the conjugation of p lone electron pairs of sulphur with neighbouring π‐electron systems on the free energy of activation for the inversion process were not observed.
Synthesis and spectroscopic studies of 2‐(1,1‐dimethylhydrazono)propyl phosphonates
Authors: Salazar Miguel , Li Ven‐Shun , Cates Lindley A.
Published: May 2005

The synthesis of diethyl 2‐(1,1‐dimethylhydrazono)propyl phosphonate (1) and its 1‐benzoyl derivative (2) is described. The 1H and 13C NMR spectra of 1 and 2 have been completely assigned with the aid of two‐dimensional 1H13C correlation NMR spectroscopy. Spectral data for ethyl α‐benzoyl‐β‐(1,1‐dimethylhydrazino)crotonate (5) were also obtained.

The results show that 1 exists predominantly in the E‐ and Z‐isomeric forms in a ratio of ca 2:1, and 2 occurs almost exclusively in the E‐form. Data for 5 indicate that this compound exists in the Z‐ and E‐forms in a ratio of ca 3:1.