bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C NMR spectra of eudesmanolides I—eudesman‐12,6‐olides
Authors: Marco J. A. , Carda M. 
Published: May 2005

AbstractThe 13C NMR spectra of 26 eudesmanolides of natural and synthetic origin have been measured, including the naturally occurring sesquiterpene lactones artemisin, torrentin, rothin‐A and rothin‐B and several semi‐synthetic eudesman‐12,6‐olides obtained from artemisin. The chemical shift values of the different compounds are compared and the effects of the substituents are discussed.
Conformational dependence of 13C SCS in 1‐methyl‐1‐phenylcyclohexanes
Authors: Cook Michael J. , Nasri Khalida A. 
Published: May 2005

Abstract13C chemical shift data are reported for a series of para‐substituted 1‐methyl‐1‐phenylcyclohexanes at 22 and ‐100 °C. The magnitudes of the SCS at alkyl and cycloalkyl carbon positions are discussed. The SCS at C‐methyl and C‐4 are significantly different in the two chair conformations. The variation at C‐methyl is appraised in terms of the orientation of the aromatic ring.
Compounds with bridgehead nitrogen 53—13C NMR spectra and stereochemistry of perhydronaphthaleno[2,1‐e]pyrido[1,2‐c][1,3]oxazines
Authors: Crabb Trevor A. , Roch Olive G. , Wood Brian 
Published: May 2005

AbstractThe configurations and preferred conformations of some diastereoisomeric perhydronaphthaleno[2,1‐e]pyrido[1,2‐c][1,3]oxazines have been assigned by 13C NMR spectroscopy. These results require reversal of two previous tentative configurational assignments based on 1H NMR spectroscopy, and also indicate the presence of non‐chair conformations for cis‐anti‐cis‐syn‐cis‐ and trans‐syn‐cis‐syn‐cis‐perhydronaphthaleno[2,1‐e]pyrido[1,2 ‐c][1,3]oxazine.
13C spin‐lattice relaxation study of chlorinated alkanes
Authors: Pitkänen Maija , Laihia Katri , Velichko F. K. , Lavrukhin B. D. 
Published: May 2005

AbstractThe spin‐lattice relaxation of ten polychloroalkanes (ethanes to pentanes) have been studied both neat and in a 50% solution in CDCl3. The T1 values for the CH2, CH2Cl and CHCl2 carbons decrease with increasing molecular weight in accordance with a dipolar‐dominated mechanism, whereas those of the CCl3 carbons showed no dependence on molecular weight. In chloropentanes, with chlorine substitution at one end only, the frequency of segmental motion begins to compete with that of overall tumbling of the molecule. Consequently, the T1 minimum is shifted from the middle towards the heavier end of the molecule, and also a relatively large T1 for the terminal methyl is observed. It was also demonstrated that the segmental motion is less dependent on solvent and concentration (viscosity) than the overall reorientation of the molecules.
13C and 15N NMR investigation of the prototropic equilibrium of 2‐hydroxy‐3‐methylindazole
Authors: Schilf W. , Stefaniak L. , Webb G. A. 
Published: May 2005

AbstractIt is shown that both 13C and 15N NMR measurements provide similar estimates of the position of the prototropic equilibrium exhibited by 2‐hydroxy‐3‐methylindazole in three solvents. The 15N NMR study of the pyridine and pyrrole types of nitrogen atoms provided the most quantitatively reliable results. The position of the prototropic equilibrium was found to be critically dependent on the acidity of the chosen solvent, the quinonoid form being predominant in weakly acidic media.
Repression of one‐bond modulations in long‐range heteronuclear 2D NMR spectra using a modified long‐range optimized heteronuclear chemical shift correlation pulse sequence
Authors: Zektzer Andrew S. , John Boban K. , Martin Gary E. 
Published: May 2005

AbstractA modified long‐range heteronuclear chemical shift correlation pulse sequence which eliminates modulations of response intensity due to one‐bond proton‐carbon [1 J(CH)] spin couplings is described. The ‘decoupling’ of one‐bond modulation has been accomplished through the use of a bilinear rotational decoupling (BIRD) pulse of the type 90° x(1H)‐τ‐180° x(1H)/180° x(13C)‐τ‐90° ‐x(1H) midway through the second magnetization transfer delay, Δ2.One‐bond modulation of response intensities over a range of optimization values is demonstrated for the simple alkaloid norharmane when long‐range optimization of the conventional heteronuclear chemical shift correlation pulse sequence is employed. The modified pulse sequence described eliminates one‐bond modulations over the same range of optimization values. Slower modulations which arise due to long‐range couplings other than that optimized for are present in both experiments.Removal of the effects of one‐bond modulation represents a potentially significant improvement in the utility of long‐range heteronuclear chemical shift correlation experiments as a tool in spectral assignments and structure elucidation.
Conformational studies of sterically comparable 2,4‐disubstituted bicyclo[3.3.1]nonan‐9‐one systems
Authors: Ravishankar Lakshmy , Rele Dinesh N. , Geetha Kunnavakam V. , Mathur Hari H. , Trivedi Girish K. 
Published: May 2005

AbstractCondensation of substituted cyclohexanones with cinnamaldehydes and morpholine in the presence of anhydrous cerium(III) chloride was carried out. The stereochemistry of the condensed products, variously substituted 2‐morpholino‐4‐phenylbicyclo[3.3.1]nonan‐9‐ones, was deduced by using the 1H NMR COSY technique and 13C NMR data. In order to draw a general conclusion, the stereochemistry of the sterically comparable 2,4‐diphenylbicyclo[3.3.1]nonan‐9‐one was also studied in detail, using 1H NMR COSY and 13C NMR data. A general conclusion regarding the boat‐chair conformational preference for such sterically comparable cis‐2,4‐disubstituted bicyclo[3.3.1]nonan‐9‐ones has been deduced, with the substituted ring in the boat form and a diequatorial disposition of the two substituents.
Conformational effect on carbon‐13 chemical shifts of substituted 3,5‐dimethylbenzenes
Authors: Salman Salman R. , Kamounah Fadhil S. 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts of sixteen 1‐X,2‐Y,4‐Z‐3,5‐dimethylbenzenes are presented. It is suggested that the conformational changes of the substituents are significant in determining the chemical shifts of these compounds. The deviation from the additivity rule is discussed.
Application of the XCORFE long range heteronuclear correlation sequence to several biphenyls and m‐quaterphenyls
Authors: Smith William B. 
Published: May 2005

AbstractA series of highly substituted biphenyls and m‐quaterphenyls have been synthesized and carbon and proton NMR spectra have been assigned by a combination of 1D and 2D techniques. The XCORFE variation of the long range heteronuclear correlation experiment was found to be particularly valuable in making assignments via H‐C‐C‐13C correlations.
3,6,9‐trioxanthracenes and 3,6‐dioxa‐9‐thianthracenes: Conformational analysis and complete assignment of 13C NMR spectra
Authors: Moreno‐Mañas Marcial , Ribas Jordi , Sánchez‐Ferrando Francisco , Virgili Albert 
Published: May 2005

AbstractThe 20.15 MHz 13C NMR spectra of five 3,6,9‐trioxanthracenes and four 3,6‐dioxa‐9‐thianthracenes have been assigned using a variety of one‐dimensional techniques. These include spin‐echo multiplicity sorting (SEFT), long‐range heteronuclear coupling constant determination via gated decoupling and selective heteronuclear 13C{1H} NOE difference spectroscopy. The axial position of substituents on C‐10 has been demonstrated.
Determination of the stabilization energy of the cyclopropylmethyl radical by EPR spectroscopy
Authors: Walton John C. 
Published: May 2005

AbstractCyclopropylmethyl radicals were generated from cyclopropylmethyl bromide and studied at low temperatures by EPR spectroscopy. From the exchange broadening in the spectra the internal rotation barrier about the C‐β‐C‐α. bond was found to be 11.5±0.8 kJ mol−1. Hence, the stabilization energy of the cyclopropylmethyl radical is 10±2.3 kJ mol−1 and DH° (cyclopropylmethyl‐H) = 400 kJ mol−1. The radical's structure, conformation and C‐β‐C‐α. rotation barrier were calculated by the semi‐empirical MNDO‐UHF method.
Metal(loid) NMR data for 1,1‐bis(trimethylmetal)alk‐1‐enes: Two‐bond metal‐metal coupling constants
Authors: Mitchell T. N. , Reimann W. 
Published: May 2005

AbstractMetal(loid) NMR data are reported for a series of 1,1‐bis(trimethylmetal)alk‐1‐enes of the type RR′CC(MMe3)(M′Me3) (M = Si, Ge, Sn, Pb; M′ = Sn, Pb). These data are commented upon briefly, with particular respect to the two‐bond metal‐metal coupling constant.Two‐bond coupling constants, heavier elements.
1H and 13C NMR spectra of peracetylated 1‐deoxy‐1‐nitroheptitols
Authors: Martinez M. Bueno , Eliel Ernest L. , Kenan William R. , Blazquez M. A. Serrano , Galan E. Roman 
Published: May 2005

AbstractThe 1H and 13C NMR chemical shifts and H‐H couplings for five peracetylated 1‐deoxy‐1‐nitroheptitols are reported. From these spectra the preponderant conformation at room temperature of each compound has been determined, and compared with other alditols with the same configuration.
Small molecule conformation in the receptor‐bound state by the two‐dimensional spin exchange experiment
Authors: Andersen Niels H. , Eaton Hugh L. , Nguyen Khe T. 
Published: May 2005

AbstractPure absorption phase two‐dimensional nuclear Overhauser spectrocopy (NOESY), using a short cycle time protocol, has been used to study cross‐relaxation between protons of ligands bound to proteins. The 2D experiment is an accurate and efficient method for determining exchange transferred NOEs. Truncated NOESY data sets (obtained in less than 3 h) for the test systems—prostaglandin F2α bound to albumin and NAD+ bound to three different dehydrogenase enzymes—provide NOE estimates within experimental error of those obtained by the more time‐consuming one‐dimensional experiments. The 2D data matrix has within it spin‐diffusion controls and cross‐relaxation spectra useful for the subtraction of unwanted signals including spin transfer from coincidentally perturbed protein resonances and t1 streaks and ridges.
Model compounds for the active site selenocysteine of glutathione peroxidase: A 77Se NMR study
Authors: Dowd Diane , Gettins Peter 
Published: May 2005

AbstractTo test the feasibility of using 77Se NMR to distinguish between different proposed mechanisms of action of the selenoenzyme glutathione peroxidase, model compounds containing the proposed selenium moieties have been synthesized and their 77Se NMR spectra recorded. It was found that the difference in chemical shift between the two proposed resting states, selenol or selenenic acid, is approximately 1300 ppm. For the next step, oxidation by hydrogen peroxide, a much smaller difference of about 100 ppm was found between selenenic and seleninic acid species. The products of the second reaction step, selenide sulfide vs selenoxide sulfide, differed in chemical shift by about 470 ppm. It was concluded that, for two of the three states of the enzyme, 77Se NMR could, in principle, be used unambiguously to distinguish between the two proposed mechanisms.
Conformation of the hypermodified purine queuine: Substrate for the enzyme transfer RNA—guanine transglycosylase
Authors: Sierzputowska‐Gracz Hanna , Agris Paul F. , Katze Jon R. 
Published: May 2005

AbstractThe hypermodified nucleotidyl purine queuine [7‐(3,4‐trans‐4,5‐cis‐dihydroxycyclopent‐1‐en‐3‐ylaminomethyl)‐7‐deazaguanine] is a substrate for transfer ribonucleic acid (tRNA) enzymes replacing guanine at nucleotide position 34 of tRNAs for the amino acids aspartic acid, asparagine, bistidine and tyrosine. The structure and conformation of native queuine was studied by one‐dimensional 13C and 1H NMR spectroscopy and by two‐dimensional NMR spectroscopy (COSY and NOESY). The structure in solution was found to be the 3,4‐trans‐4,5‐cis‐dihydroxycyclopent‐1‐ene form. The plane of the cyclopentene ring is probably perpendicular to that of the purine ring structure.
13C and 15N NMR studies of 1,2‐benzisoxazole 2‐oxides, 1,2‐benzisoxazoles and 2‐hydroxyaryl ketoximes
Authors: Tsoungas Petros G. , De Costa Bruce F. 
Published: May 2005

Abstract13C and 15N chemical shift assignments of a number of 1,2‐benzisoxazole 2‐oxides and their deoxygenated analogues are reported and discussed. Similarly, assignments for some of the precursors to the N‐oxides, o‐hydroxyaryl ketoximes, are reported. In the N‐oxides the “push‐pull” effect of the NO dipole is largely localized on the isoxazole unit. A large (ca 39 ppm) upfield shift of the C‐3 resonance is caused by the exocyclic oxygen whereas C‐7a and, to a lesser extent, C‐6 are the most heavily deshielded nuclei. The substituents do not have a significant effect on the C‐3 resonance, whereas their effect on the carbocyclic carbons is more pronounced, the most markedly affected being the C‐4 and C‐6 nuclei. N‐Oxidation of 1,2‐benzisoxazole causes a large (50.5 ppm) shielding of the 15N nucleus.
Modulation of methylene carbon response intensity in long‐range heteronuclear 2D NMR chemical shift correlation spectra
Authors: Salazar Miguel , Zektzer Andrew S. , Martin Gary E. 
Published: May 2005

AbstractSeveral recent papers have dealt with the modulation of protonated carbon response intensities in long‐range heteronuclear 2D NMR chemical shift correlation spectra. Expressions describing the one‐bond modulation of the response intensity of the C‐3 methylene resonance of 6,7‐dimethoxy‐3,4‐dihydroisoquinoline, and the decoupling of this modulation afforded by a BIRD pulse located midway through the Δ2 refocusing delay, are presented with experimental confirmation. Long‐range response intensities are related to the conventional heteronuclear chemical shift correlation spectrum optimized for transfer from the directly attached proton.
Carbon‐13 NMR spectra of some disubstituted diamantanoid compounds
Authors: Horská Alena , Podehradská Jaroslava , Vodička Luděk , Hájek Milan , Trška Petr 
Published: May 2005

AbstractThe 13C NMR spectra of eleven hydroxy and oxo derivatives of methyl esters of 1‐ and 4‐diamantane carboxylic acids, three hydroxy derivatives of diamantanone and six dibromo derivatives of diamantane have been measured in CDCl3 or C6D6 solutions. The signals were assiged by the additivity rule. The 13C NMR spectra of all compounds were described by two parameters, e.g. the sum of the 13C chemical shifts of all carbon atoms in the measured compounds (SCCS) and the ratio of the number of carbon atoms (Nc) and theoretical number of signals (Ns).
γgauche effects in the 1H and 13C NMR spectra of steroids
Authors: Hammann P. E. , Habermehl G. G. , Kluge H. 
Published: May 2005

Abstractγgauche effects of 12‐substituted‐14β‐hydroxy‐ and 14α‐steroids were studied by 1H and 13C NMR spectroscopy. A linear correlation was found between the 1H chemical shift of 4H‐17 and the 13C shift of C‐17 for C‐12‐substituted steroids. This correlation can be explained by steric interactions.
13C NMR spectra of some novel 2(5H)‐furanone and 3(2H)‐furanone derivatives
Authors: Kuipers William J. , Mack Robert A. , Georgiev Vassil St. 
Published: May 2005

AbstractThe 13C NMR spectra of a series of novel 2(5H)‐furanones were studied. The assignments of the carbon resonances were made on the basis of chemical shifts, long‐range carbon‐hydrogen couplings, intarnal comparison and known reference sources.
13C T1 NMR study of arylmercury compounds. Barriers to rotation about the carbon–mercury bond
Authors: Thomas Ruthanne D. , Rowland Keith E. 
Published: May 2005

AbstractBarriers to rotation about the preferred axis, C‐4HgC‐4′, were determined for diphenyl‐, bis(o‐tolyl)‐ and bis(m‐tolyl)‐mercury from 13C T1 relaxation times as a function of temperature in DMSO and in 1,1,2,2‐tetrachloroethane–CCl4. Based on results for the unsymmetrical compound phenyl(o‐tolyl)mercury, the rotation about the preferred axis is interpreted as rotation about the carbon–mercury bond. The average barrier to internal rotation of 3.6 ± 0.6 kcal mol−1 is constant as a function of both methyl substitution and coordinating and non‐coordinating solvents.
Effect of N‐substituents on the 13C NMR parameters of azoles
Authors: Begtrup Mikael , Elguero José , Faure Robert , Camps Pelayo , Estopá Carmen , Ilavský Dušan , Fruchier Alain , Marzin Claude , de Mendoza Javier 
Published: May 2005

AbstractThe 13C chemical shifts and a large collection of coupling constants have been measured for 169 N‐substituted azoles with no other substituents on the ring. Simple additive models have been used to discuss both the chemical shifts and the coupling constants. The chemical shift of the substituent depends on the nature of the azole which can, accordingly, be classified into three to six families. Some structural problems (ring‐chain isomerism of 1‐trifluoromethylsulphonyl‐1,2,3‐triazole, silylotropy and stannotropy) are also discussed.
13C NMR spectra of para‐substituted methoxybenzenes and phenols in the solid state: Examination of chemical shift non‐equivalence in ortho and meta carbons related to non‐equivalent electron distribution, and application to assignment of peaks in meso‐hexestrol and its derivatives
Authors: Saitǒ Hazime , Yokoi Motoko , Aida Misako , Kodama Masahiko , Oda Taiko , Sato Yoshihiro 
Published: May 2005

Abstract13C NMR spectra of para‐substituted methoxybenzenes and phenols were recorded in the solid state to gain an insight into the manner and origin of substantial peak splittings in the ortho (up to 9.2 ppm) and meta (up to 2.5 ppm) carbon signals. It was difficult to account for these peak splittings only by the steric interaction with the methyl group of the substituent, because their magnitude varied widely from 4.6 to 9.2 ppm with a variety of substituents at the para position, and the meta carbon peaks are also split into doublets. Instead, it was found that the electron density non‐equivalence between the two ortho and the two meta carbons is mainly responsible for the splittings, as manifested by the presence of an approximate linear relationship between the displcements of the 13C NMR peaks and total electron density. The observed additional splitting in the 13C NMR spectra of meso‐hexestrol and its methyl or ethyl ether(s) in the solid state was similarly explained. Stereochemical features of these molecules in the solid state are discussed on the basis of the 13C NMR data.
Solution structure of porphyrin aggregates determined by 1H NMR ring current shifts. II. Conformations of dimers and higher aggregates of water‐soluble porphyrins
Authors: Koehorst R. B. M. , Hofstra U. , Schaafsma T. J. 
Published: May 2005

AbstractThe aggregation of the water‐soluble porphyrins tetra(4‐carboxyphenyl)porphyrin free base (H2TPPC), tetra(4‐N‐methylpyridyl)porphyrin free base (H2TMPyP) and their zinc derivatives (ZnTPPC and ZnTMPyP) was studied by 1H NMR and optical absorption spectroscopy. In the solvent H2OCH3OH (4:1), mixing of the anionic H2TPPC or ZnTPPC with the cationic H2TMPyP or ZnTMPyP yields various types of “hetero” aggregates. Only H2TPPC forms “homo” aggregates in this solvent. Addition of 1 m KCl results in an increase in the aggregation of H2TPPC and also enhances the aggregation of ZnTPPC. The structures of the “hetero” aggregates are stacks of the oppositely charged porphyrins in an alternating order. However, when one of the constituents is H2TPPC, aggregates having structures of the “homo” type are also formed. The 1H NMR ring current shifts are accounted for by identical conformations of dimers, and dimer structures in trimers and higher aggregates of the “hetero” type.
Assignment of 1H and 13C NMR spectra and conformation of 8,8‐diethyl‐N,N‐dimethyl‐2‐aza‐8‐germaspiro[4.5]decane‐2‐propanamine dihydrochloride (spirogermanium)
Authors: Sarrazin M. , Peyrot V. , Briand C. , Faure R. 
Published: May 2005

Abstract1H and 13C chemical shifts, obtained by two‐dimensional homonuclear and heteronuclear shift correlation, are reported for 8,8‐diethyl‐N,N‐dimethyl‐2‐aza‐8‐germaspiro[4,5]decane‐2‐propanamine dihydrochloride (spirogermanium). The chemical shift variations as a function of pH and the coupling constants of the azacyclopentane moiety of the molecule are analysed, and a conformation is proposed for the molecule.
Carbon‐13 nuclear magnetic resonance spectra of brominated catechin derivatives: Stereoelectronic effects on chemical shifts
Authors: Kiehlmann E. , Tracey A. S. 
Published: May 2005

AbstractThe 13C NMR spectra of 21 catechin derivatives substituted at C‐6/C‐8 by bromine and/or hydrogen and at oxygen by methyl, acetyl and/or hydrogen have been analysed in deuteriated acetone and chloroform. When a methoxy group is flanked by two bulky ortho substituents (6‐Br and C‐4), the MeO and ortho/para ring carbons (C‐4a, C‐6, C‐8) are deshielded owing to steric inhibition of resonance, which permits a distinction between 6‐ and 8‐substituted catechin methyl ethers. Hindered acetoxy groups do not give rise to this phenomenon.
Assignments of the 1H and 13C NMR resonances of cadinanes and bicadinane by means of two‐dimensional shift‐correlated NMR techniques
Authors: Kruk C. , Cox H. C. , De Leeuw J. W. 
Published: May 2005

AbstractTwo‐dimensional 1H and 13C shift‐correlated NMR experiments have been used for the unambiguous assignments of all proton and carbon chemical shifts of two cadinanes and bicadinane.
Variable‐temperature NMR studies of thyroid hormone conformations
Authors: Gale Douglas J. , Craik David J. , Brownlee Robert T. C. 
Published: May 2005

Abstract1H NMR spectra at 300 and 400 MHz have been recorded for the thyroid hormones thyroxine (T4) and triiodothyronine (T3) over a range of temperatures from 175 to 298 K in MeOH‐d4. Above 200 K the aromatic region of the NMR spectrum of T4 consists of two peaks, one for the H‐2′, H‐6′ protons and one for H‐2,H‐6. As the temperature is lowered each of these resonances first broadens and then splits into two peaks of equal intensity at low temperature. This is consistent with slowed exchange between two equally populated conformers. Similar behaviour is noted for T3, although in this case the spectrum is complicated by the presence of spin‐spin splitting. Consideration of coalescence temperatures and a line‐shape analysis yielded activation barriers in the range 35–38 kJ mol−1. It is concluded that the observed spectral changes are due to dynamic interconversion between proximal and distal forms of the hormones, and that the interconversion takes place by cooperative rotations around the bonds between each phenyl ring and the linking oxygen atom.
Stereochemistry of hexakis (3‐methoxyphenyl) benzene and hexakis(3‐methylphenyl) benzene. An incremental chemical shift model for meta‐substituted hexaphenylbenzenes
Authors: Pepermans Henri , Willem Rudolph , Gielen Marcel , Hoogzand Cornelis 
Published: May 2005

AbstractThe 1H NMR spectrum of hexakis(3‐methoxyphenyl)benzene exhibits a methoxy absorption which looks exactly like a triplet. The spacing between the signals is, however, proportional to rather than independent of the field strength. The aryl H‐5 region of this compound and the methyl region of hexakis(3‐methylphenyl)benzene display similar field‐proportional, triplet‐like splittings. This property of meta‐substituted hexaphenylbenzenes cannot be explained by either preferential or residual isomerism, even in the presence of many accidental isochronies. A chemical shift model based on the hypothesis that the meta substituents do not disturb the geometry of the hexaphenylbenzene skeleton or the populations of the rotamers explains the spectra in a straightforward manner.
ESR and ENDOR studies on the radical anions of some arylethenes and arylacetylenes
Authors: Gerson Fabian , Goldberg Ira B. , McKinney Ted M. 
Published: May 2005

AbstractThe radical anions of (E)‐1, 2‐di(1‐naphthyl)ethene, (E)‐1, 2,‐di(1‐napthyl)acetylene, di(1‐naphthyl)diacetylene, 9, 10‐bis(phenylethynyl)anthracene and di(9‐anthryl)acetylene have been characterized by ESR and ENDOR spectroscopy. Their proton hyperfine data and g factors are briefly discussed.