bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractProton 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

Abstract13C 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

Abstract13C 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

AbstractA 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

AbstractProton 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

AbstractComplete 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

AbstractThe 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

AbstractCarbon‐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

AbstractProton 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

AbstractOn 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

AbstractAdenosine, 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

AbstractThe 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

AbstractA 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

AbstractFluorine‐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

AbstractRelayed 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

AbstractThe 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

Abstract1H 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

Abstract13C 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

AbstractPerindopril, 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

AbstractLow‐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

Abstract13C 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

AbstractSeparate 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

AbstractCyclopent‐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

AbstractMaltitol 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

Abstract13C 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

AbstractThe 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

AbstractBarriers 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

AbstractThe 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.