bluuebunny/crossref_metadata_2025_split huggingface dataset:
Halogeno‐substituted 2‐ and 3‐methylbenzo[b]thiophenes: Use of 1H NMR spectral analysis and 1H{1H} nuclear Overhauser effect for locating the halogen substituent
Authors: Cuberes Ma. Rosa , Moreno‐Mañas Marcial , Sánchez‐Ferrandom Francisco 
Published: May 2005

AbstractThirty‐seven halogeno‐substituted 2‐ and 3‐methyl‐(or halogenomethyl)‐benzo [b]thiophenes, including 17 new compounds, were prepared. The constitution of 14 of these was confirmed by full analysis (LAOCOON) of their 80 MHz1HNMR spectra and by 1H{1H} NOE measurements. In this way a by‐product from the preparation of 4‐ and 6‐bromo‐3‐bromomethylbenzo[b]thiophenes was shown conclusively to be 5‐bromo‐3‐bromomethylbenzo[b]thiophene. The 3‐substituted benzo[b]thiophenes showed greater NOE enhancement factors at H‐4 than at H‐2 when the 3‐methyl or halogenomethyl substituent was irradiated.
Secondary structure of peptides. 17—Cis/trans isomerism of solid proline‐containing oligopeptides as revealed by 13C NMR CP/MAS spectroscopy
Authors: Kricheldorf Hans R. , Haupt Erhard T. K. , Müller Detlef 
Published: May 2005

AbstractThe 75.4 MHz 13C NMR CP/MAS spectra of five classes of solid proline peptides were measured: cyclodipeptides, unprotected dipeptides, N‐tert‐butoxycarbonyl‐ (Boc) or N‐benzyloxycarbonyl‐ (Z)‐proline derivatives and N‐protected peptides with an aminoacyl—proline bond. In the case of solid N‐protected proline derivatives, the shift difference (Δδ) of the C‐β and C‐γ signals mainly reflects the cis/trans isomerism of the XPro bond, with Δδ = 3‐5 ppm being characteristic of trans and 7‐11 ppm of cis isomers. However, in the case of solid cyclodipeptides and unprotected dipeptides, the individual crystal lattices also affect the conformation of the side chain, so that the C‐β and C‐γ‐signals are not reliable indicators of the cis/trans isomerism.When the N‐protected proline derivatives were crystallized slowly from various solvents, the N‐Boc‐ and N‐Z‐proline derivatives exclusively yielded the cis isomer, even when the cis/trans equilibrium in solution favoured the trans isomer. In the case of N‐aminoacylprolines, the trans isomer crystallized almost exclusively. Oligopeptides containing two proline units, such as ZProProOH or ZGlyProGly GlyProAlaOH, may possess a cis and a trans bond in the same molecule.
1H, 13C and 15N NMR observations on the protonation of 1‐ and 3‐deazapurine
Authors: Lindon J. C. , Williams J. M. , Barraclough P. 
Published: May 2005

AbstractUsing 1H, 13C and 15N NMR it has been concluded that 3‐deazarpurine protonates exclusively at N‐1 with a pK of about 5.6. The base exhibits rapid tautomerism with proportions of 70:30, with the N–7‐H tautomer in the majority. The salt exists predominantly as the N‐7‐H tautomer. 1‐Deazapurine protonates essentially in a 1:1 ratio at N‐3 and at the imidazole ring, with a pK of about 3.1. This base also exhibits rapid tautomerism with proportions of 30:70, this time with the N‐9‐H in the majority. The salt also exists in a tautomcric mixture with approximately equal proportions. One form has N‐3 and N‐9 bearing hydrogens and the other has N‐7 and N‐9 bearing hydrogens.
Structure determination of peracetylated glycosphingolipids by one‐ and two‐dimensional 1H NMR at 360 and 500 MHz
Authors: Dabrowski Janusz , Dabrowski Ursula , Hanfland Peter , Kordowicz Maria , Hull William E. 
Published: May 2005

AbstractThe analysis of two‐dimensional proton shift‐correlated 500 MHz NMR spectra of several peracetylated glycosphingolipids confirmed that peracetylated oligosaccharides are particularly well suited for the identification of the constituent sugar residues and the elucidation of the sites of glycosidic linkage. Although a number of partial sequences could be determined by inter‐residue nuclear Overhauser effect or long‐range scalar coupling across the glycosidic bonds, the full sequence determination of larger oligosaccharides has several limitations owing to experimental difficulties and possible ambiguities in assignments due to signal overlap. The following peracetylated glycosphingolipids were investigated by two‐dimensional methods at 500 MHz: Galα(1→4)Galβ(1→4)Glcβ(1→1)Cer (Cer = ceramide), GalNAcβ(1→3)Galα(1→4)Galβ(1→4)Glcβ(1→1) Cer (globoside) and Galα(1→3)Galβ(1→4)GlcNAcβ(1→3)Galα(1→3)Galβ(1→4)GlcNAcβ(1→6)Galβ(1→4)GlcNAcβ(1→3)Galβ(1→4)Glcβ(1→1)Cer. To compare the potential of one‐ and two‐dimensional methods, the spectra of peracetylated Galβ(1→4)Glcβ(1→1)Cer, Galβ(1→4)GlcNAcβ(1→3)Galβ(1→4)Glcβ(1→1)Cer. To compare the potential of one‐ and two‐dimentional methods, the spectra of peracetylted Galβ(1→4) Glcβ(1→1)Cer were assigned with the aid of spin‐decoupling difference spectroscopy at 360 MHz.
Geometry‐dependent complexation effects in 13C NMR spectra of (η6‐[n]paracyclophane)‐chromium and ‐iron complexes
Authors: Mori Nobuo , Takamori Michiko 
Published: May 2005

AbstractRelationships between molecular geometry and complexation offects in 13C NMR spectra are reported for series of tricarbonyl (η6‐[n]paracyclophane)chromium complexes and (η6‐[n]paracyclophane) (η5‐cyclopentadienyl)iron(II) hexafluorophosphates, where n is 8, 9, 11, 12 and 15. In the Cr complex series in CDCl3, the complexation shift (Δδ) for the aryl tertiary carbon increases with a decrease in n, from 34.5 (n = 15) to 37.9 ppm (n = 8), whereas Δδ for the aryl quaternary carbon decreases from 27.9 to 22.0 ppm. Similar changes in Δδ with n are found in the Fe complex series, except that their Δδ values are larger. This dependence of Δδ on n is directly related to the interatomic distance between the metal and the ligand carbon. In addition, a significant geometry dependence of the complexation effects is observed for the benzylic‐ and the cyclopentadienyl‐carbon resonances, but not for the one bond aryl C–H spin–spin couplings.
Conformational analysis of DL‐, L‐ and D‐methionine by solid‐state 13C NMR spectroscopy
Authors: Díaz Luis E. , Morin Frederick , Mayne Charles L. , Grant David M. , Chang Ching‐jer 
Published: May 2005

AbstractThe conformational analysis of DL‐, L‐ and D‐methionine was studied by solid‐state 13C NMR with the help of cross‐polarization and magic‐angle spinning techniques. The spectrum of commercial crystalline DL‐methionine showed two chemical shifts (18.7 and 15.8 ppm) for the methyl carbon. Crystallization from water or water‐ethanol (95 : 5) allowed the separation of two crystalline forms (α and β), of which one had δ (CH3) 18.7 ppm and the other δ (CH3) 15.8 ppm. Therefore, each crystalline form of DL‐methionine consists of a single conformer, a result in agreement with x‐ray diffraction data. This conformational difference of the two crystalline forms was also reflected in the carbon resonances of C‐β and C‐γ. When L‐ and D‐methionine were crystallized from water‐ethanol (3 : 2), the solid‐state 13C NMR spectra showed that each isomer displayed two methyl carbon peaks at 18.1 and 16.2 ppm of equal intensities, while the α‐carbon resonances showed a broad peak due to two unresolved doublets. These results suggest that the L‐ or D‐methionine crystal contains two different conformers in one unit cell, a conclusion that is also supported by the x‐ray data.
Conformational study of chiral acyclic ketones by 1H and 13C NMR. I. (±)‐2,2,6,6‐tetramethyl‐5‐phenylheptan‐3‐one
Authors: Alvarez‐Ibarra C. , Arias‐Pérez M. S. , de Andrés A , Balcázar J. L. 
Published: May 2005

AbstractThe conformational analysis of a chiral acyclic ketone with one asymmetric carbon, (±)‐2,2,6,6‐tetramethyl‐5‐phenylheptan‐3‐one, has been achieved for the first time by means of an x‐ray diffraction study and the analysis of 1H1H and 13C1H geminal and vicinal coupling constants and 13C1H direct coupling constants. The application of the Durette‐Horton, Pachler and Altona empirical equations supports the hypothesis of a marked predominance in solution of the conformation observed in the solid state.
1H and 13C NMR studies on nitrosonaphthols, and their complexation with the dioxouranium(VI) ion
Authors: Vainiotalo Anto , Vepsäläinen Jouko 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of 1‐nitroso‐2‐naphthol and its disodium 3,6‐disulphonate, 2‐nitroso‐1‐naphthol and its sodium 4‐sulphonate and the complexes of the sulphonated ligands with dioxouranium(VI) were recorded and analysed. The results show the nitrosonaphthols exist predominantly in the oxime form, and that the 1‐nitroso compounds have a preferred structure. The quinonoid oxygen does not take part in the complexation with dioxouranium(VI), which is effected by chelation through the oxime oxygen and nitrogen.
Non‐additive carbon‐13 NMR substituent chemical shifts. II—1,3‐disubstituted benzenes
Authors: Bromilow John , Brownlee Robert T. C. , Craik David J. , Sadek Maruse 
Published: May 2005

AbstractAromatic 13C chemical shifts are reported for an extensive set (15 common substituents) of 1,3‐disubstituted benzenes measured at low concentration in deuteriochloroform. The substituent chemical shift data show systematic non‐additivity. Data for the para‐ and two meta‐positions to the variable substituent were analysed using the recently developed non‐linear resonance (DSP‐NLR) and standard (DSP) dual substituent parameter equations. It is shown for these positions that mutual substituent interaction is responsible for the non‐additive shifts and that (a) this interaction has both an inductive (polar) and a resonance component, even for meta‐oriented substituents, and (b) the shift‐charge ratio term extends past the ipso‐position. These results are discussed in terms of local paramagnetic shielding contributions to 13C shifts.
Deuterium isotope effects on the 13C nuclear shielding of intramolecularly hydrogen‐bonded systems
Authors: Hansen Poul Erik 
Published: May 2005

AbstractA large number of intramolecularly hydrogen‐bonded molecules were investigated by means of deuterium isotope effects on 13C nuclear shielding. The compounds illustrate three different types of molecules: compounds with a localized hydrogen bond (strongly asymmetric double minimum potential), and tautomeric molecules of symmetrical or unsymmetrical nature (symmetrical or almost symmetrical double minimum potential). In the localized case the strength of the hydrogen bond reflects itself in the magnitude of 2Δ COD. The presence of a hydrogen bond is, furthemore, demonstrated in an orientational dependence of 3Δ COD, and usually also in the presence of an 3Δ COD. The tautomeric systems can also be characterized by means of deuterium isotope effects. Investigations of β diketones showed the presence of an equilibrium isotope effect. Large long‐range isotope effects of naphthazarin are explained in a similar manner. Tautomerism was established in usnic acid and the type of tautomerism was determined. 2,6‐Dihydroacetophenone shows an interesting type of perturbation of the equilibrium on unsymmetric deuteriation.
Conformational analysis of a synthetic carboxylic ionophore in solution by 1H NMR spectroscopy
Authors: Kuboniwa Hitoshi , Yamaguchi Kazuo , Hirao Akira , Nakahama Seiichi , Yamazaki Noboru 
Published: May 2005

AbstractThe 1H NMR spectra of the potassium salt of a synthetic polyether carboxylic ionophore, HO[CH2CH2O(1,2‐C6H4)O]4CH2 (1,2‐C6H4)COOH (1), in CDCl3 were assigned by two‐dimensional NMR methods (2D chemical shift correlation and 2D NOE). The gauche conformer about the C—C bond of the 1,2‐dioxyethylene groups of the potassium salt of 1 were found to be predominant from the analysis of the proton‐proton vicinal coupling constants. Based on rotamer population analysis, together with nuclear Overhauser effect data, the preferred conformation of the potassium salt of 1 in the solution was estimated.
Studies on the substituent dependence of 1H chemical shifts. Unusual 1H shifts in trans‐9‐halogenodecalins
Authors: Schrumpf G. , Sanwald W. , Machinek R. 
Published: May 2005

AbstractThe 1H, 2H and 13C spectra of trans‐9‐chloro, ‐bromo‐ and ‐iodo‐decalins and their deuteriated analogues have been recorded in order to study the effect of chloro, bromo and iodo substituents on β antiperiplanar protons. All shifts were completely assigned. Unusually large upfield shifts were detected for β protons antiperiplanar to the halogen substituents. The electronegativity dependence of the β shifts is opposite to that hitherto reported.
13C NMR studies of the friedelane series of triterpenoids and the conformation of the D and E rings in friedelan‐7‐one
Authors: Prakash Om , Roy Raja , Garg H. S. , Bhakuni D. S. 
Published: May 2005

AbstractThe 13C chemical shifts in the spectra of friedelan‐7‐one (1), methyl 3‐oxofriedelan‐25‐oate (2), methyl friedelan‐25‐oate (3), 7‐oxofriedelan‐3‐α‐yl acetate (4), friedelan‐3‐one (5), 2‐hydroxy‐3, 4‐seco‐friedelan‐3‐oic acid (6), methyl 2‐oxo‐3,4‐seco‐friedelan‐3‐oate (7), methyl 2‐hydroxy‐3,4‐seco‐friedelan‐3‐oate (8) and 3,4‐seco‐friedelan‐2,3‐diol (9) have been fully assigned using two‐dimensional heteronuclear correlation NMR spectroscopy, BB proton decoupled, DEPT and selective heteronuclear spin decoupling methods. These assignments and the observation of substantial NOEs between 26‐methyl and 28‐methyl and between 28‐methyl and 30‐methyl support the boat to boat conformations for the D and E rings in 1. Corrections and correlations are made of some earlier literature assignments of friedelanones.
1H NMR parameters of chlorinated biphenyls
Authors: Yanagisawa Masaru , Hayamizu Kikuko , Yamamoto Osamu 
Published: May 2005

AbstractComplete analyses of the 400 MHz 1H NMR spectra of 47 chlorinated biphenyls (PCBs) were carried out in order to obtain the 1H chemical shifts and coupling constants. The 1H chemical shifts and the coupling constants on the biphenyl ring are interpreted by additive contributions from the substituent effects of chlorine atoms.
Steric effects in the 17O NMR spectroscopy of aromatic methyl ethers
Authors: Wysocki M. A. , Jardon P. W. , Mains G. J. , Eisenbraun E. J. , Boykin D. W. 
Published: May 2005

Abstract17O NMR spectroscopic data (natural abundance) were obtained for 19 methoxy‐aromatic compounds: a series of substituted anisoles with a single ortho substituent, a series of 2, 6‐disubstituted anisoles, a series of 3‐substituted‐1, 2‐dimethoxybenzenes and three multi‐substituted anisole derivatives. The chemical shifts of the highly hindered methoxy compounds are related to previously reported regiochemistry, spectroscopic results and from theoretical calculations for these compounds.
Stereostructural and NMR study of isomeric oxazines fused to the norbornane or norbornene skeleton
Authors: Sohár Pál , Pelczer István , Stájer Gáza , Bernáth Gábor 
Published: May 2005

AbstractNorbornane‐ or norbornene‐fused 2‐aryldihydro‐1,3‐oxazines, ‐1,3‐oxazin‐2‐ones and – 1,3‐oxazine‐2‐thiones were synthesized and studied by 1H and 13C NMR spectroscopy to reveal the spectral effects of the saturation of the skeleton, diexo or diendo ring annellation and isomerism in compounds containing the oxygen and nitrogen hetero atoms in isomeric positions.
Use of J‐modulated spin echoes for approximate estimation of one‐bond CH coupling constants in 13C NMR
Authors: Molin Håkan 
Published: May 2005

AbstractThe J‐modulated spin‐echo pulse sequence can be used for the approximate estimation of one‐bond CH coupling constants in complicated spectral regions. The usefulness of this technique for spectral assignment purposes is demonstrated for a beta‐lactam compound.
Determination of the rα structures of ethylene and 1,1‐difluoroethylene by NMR of partially oriented molecules allowing for correlated deformation
Authors: Wasser R , Diehl P 
Published: May 2005

AbstractThe rα structures of ethylene and 1,1‐difluoroethylene have been determined by NMR of partially oriented molecules, considering the interaction between the solute molecule and the liquid crystal solvent which leads to a correlation between molecular vibration and rotation. The analysis of the data also provides the interaction parameters which characterize the torques acting on the individual molecular bonds, deforming and simultaneously orienting the solute. A linear relationship between the interaction parameters for the C  H bonds of the two solutes and methane in the same solvents has been found.
NMR spectra of the porphyrins 32—Conformational analysis of Pyrrolidine and 3‐Hydroxypyrrolidine using CoIII meso‐Tetraphenylporphyrin (CoTPP)
Authors: Abraham Raymond J. , Medforth Craig J. 
Published: May 2005

AbstractThe geometry of pyrrolidine and 3 hydroxypyrrolidine CoTPP complexes has been investigated by 1H NMR spectroscopy. The observed couplings and ring current shifts for pyrrolidine‐CoTPP are consistent with an envelope conformation with the nitrogen atom out of the ring plane and equatorial coordination of the cobalt atom. A complete analysis of the spectrum was not possible owing to close‐coupling of the β‐protons.For 3‐hydroxypyrrolidine CoTPP two components in the ratio 85 : 15 were observed in the proton spectrum. The spectra of both compounds were completely analysed to give all the couplings in the five‐membered rings, and from these the ring conformations were deduced. The major (endo) component exists in an envelope conformation with C‐2 out of the plane of the other atoms, and the hydroxy group cis to the NH proton, both in pseudo‐axial orientations. The minor (exo) component is also in an envelope conformation, with C‐5 out of the plane of the other atoms and the hydroxyl group now trans to the NH proton.The energy difference of ca 1 kcal mol−1 (4 kJ mol−1) in favour of the endo component was reproduced by theoretical (MNDO) calculations for protonated hydroxypyrrolidine, but not for the free base. This suggests that the stabilization of the endo component is due to the electrostatic attraction of the hydroxy group and positively charged nitrogen atom.
1,3‐dinitroso‐, 1‐nitroso‐3‐nitro‐, and 1,3‐dinitro‐1,3‐diazacycloalkanes. A multinuclear NMR study
Authors: Willer Rodney L. , Moore Donald W. 
Published: May 2005

AbstractA series of five‐, six‐, and seven‐membered 1,3‐dinitroso‐, 1‐nitroso‐3‐nitro‐, and 1,3‐dinitro‐1,3‐diazacycloalkanes were investigated by 1H, 13C, and 15N NMR spectroscopy. Hindered rotation of the nitrosamine group leads to the existence of rotational isomers. The relative populations of rotamer forms are determined by steric and electrostatic interactions between nitroso groups and the remainder of the molecule, and by the size of the ring.
Long‐range CH correlation 2D NMR spectroscopy 3—long‐range J modulation of cross‐peak intensities
Authors: Krishnamurthy V. V. , Casida John E. 
Published: May 2005

AbstractIn long‐range heteronuclear chemical shift correlation experiments, modulation of the response intensities of cross‐peaks due to other long‐range couplings to the carbon, although slower than that by direct couplings, must be taken into consideration in optimizing the polarization transfer (Δ1) and refocusing (Δ2) delays. The long‐range modulation is experimentally confirmed using the standard CH correlation pulse sequence with a BIRD pulse midway through the refocusing delay. Analysis of aromatic correlations using hypothetical coupling constants shows that, in general, a choice of Δ2 = 0.667Δ1 is better than Δ2 = Δ1 for CCH correlations, particularly when other interfering long‐range couplings are involved. Guidelines for choosing optimal delays are given by response intensity and attenuation factor contours as a function of J and Δ1 values.
15N NMR spectra of wyosine (Y‐nucleoside) triacetate and its 7‐methyl congener. Chemical shifts and 15N,1H coupling constants
Authors: Glemarec C. , Remaud G. , Chattopadhyaya J. 
Published: May 2005

AbstractThe 15N chemical shifts and 15N,1H coupling constants of wyosine (Y‐nucleoside) triacetate were obtained through both fully proton‐coupled and selectively decoupled 15N NMR spectra at natural isotopic abundance, using modified INEPT pulse sequences. The spectra were analysed for 2J, 3J and 4J(NH) values. The results were compared with those for the parent compounds.
Two‐dimensional POMMIE J(CH)‐resolved 13C NMR spectrum editing. Application to peptide and carbohydrate derivatives
Authors: Coxon Bruce 
Published: May 2005

AbstractA pulse sequence has been implemented for two‐dimensional POMMIE J(CH)‐resolved 13C NMR spectroscopy and has been used to explore three methods for the automated acquisition of data for two‐dimensional spectrum editing. In the first two methods, sets of three two‐dimensional data matrices are acquired in either sequential or interleaved modes, by use of three values, π = ϕ/6, π/2 and 5π/6, for the phase shift of the multiple quantum read pulse. Computation of linear combinations of these three data matrices by use of a Pascal program that had been written earlier for two‐dimensional DEPT spectrum editing yielded two‐dimensional POMMIE J(CH)‐resolved CH, CH2 and CH3 subspectra. In the third method, these subspectra are constructed directly during acquisition, by rotation of the phase shifts of the multiple quantum read pulse and the receiver. Selected small peptides and carbohydrate derivatives were used as model compounds for this study, and their 1H and 13C NMR assignments were confirmed by two‐dimensional COSY and heteronuclear CH chemical shift correlation techniques. The results show that if appropriate equipment is available, the two‐dimensional POMMIE method is easier to implement for J(CH)‐resolved spectral editing than the two‐dimensional DEPT technique. However, these methods are comparable in their ability to suppress residual signals.
Evaluation of pulse sequences combining 13C‐1H shift correlation and heteronuclear J spectroscopy with full 1H‐1H decoupling
Authors: Perpick‐Dumont Marion , Reynolds William F. , Enríquez Raúl G. 
Published: May 2005

AbstractThree different two‐dimensional 13C‐1H shift‐correlation sequences which detect 1H chemical shifts and one bond 13C‐1H[J(CH)] couplings in f1 with full 1H‐1H decoupling are described and evaluated. They are particularly useful for detecting small differences in 1J(CH) for non‐equivalent methlene groups in natural products and other complex organic molecules. The best of the three allows determination of 1J(CH) and 1H chemical shifts to a precision better than 1 Hz, with sensitivity comparable to previous shift‐correlation and J‐resolved pulse sequences. 1J(CH) Values for a typical alkaloid suggest that these parameters are a useful probe of conformational, electronic and ring size effects in natural products.
Preparation and carbon‐13 NMR study of 3‐ and 20‐methylene analogues of steroid hormones
Authors: Gonzalez Mario D. , Burton Gerardo 
Published: May 2005

Abstract20‐Methylpregna‐4,20‐dien‐3‐one and the corresponding 17α‐hydroxy, 20‐hydroxymethyl and 17α‐hydroxy‐20‐hydroxymethyl derivatives were prepared from the 20‐keto compounds by Wittig reaction or a modified Simmons‐Smith reaction. The 13C NMR spectra of these steroids and of 3‐methylene derivatives are analysed. Solvent effects produced by addition of methanol‐d4 in the spectra of the 20‐methylene steroids are correlated with intramolecular hydrogen bonding in the corresponding 20‐ketosteroids.