bluuebunny/crossref_metadata_2025 huggingface dataset:
13C and 1H NMR chemical shifts of 9‐alkyltriptycenes. Linear variations of 13C chemical shifts on successive substitution of the 9‐methyl hydrogen atoms by methyl groups
Authors: Imashiro Fumio , Hirayama Kei , Saika A.
Published: May 2005

13C and 1H NMR chemical shifts of 9‐methyltriptycene (2), 9‐ethyltriptycene (3), 9‐isopropyltriptycene (4) and 9‐tert‐butyltriptycene (5) were measured. The 13C chemical shifts of the carbon atoms at each corresponding position in 2‐5 are proportional to the number of β‐methyl carbon atoms attached to the 9‐methyl (C‐α) carbon atom. Relatively small changes in the 13C chemical shifts of C‐2, C‐3 and C‐4 carbon atoms and nearly constant values for the 1H chemical shifts of the H‐2, H‐3 and H‐4 protons in 2‐5 suggest that the structures of the benzene rings in the 9‐alkyltriptycenes remain almost unaltered, resulting in linear variations of the 13C chemical shifts of the 9‐alkyltriptycenes.
13C NMR of acyloxyalkoxycarbenium salts. Cations formed in reactions of lewis acids with acid chlorides obtained from half‐esters of dicarboxylic acids
Authors: Eyley Stephen C. , Heaney Harry , Sodhi Khushbir S.
Published: May 2005

3‐Methoxycarbonylpropanoyl chloride and 4‐methoxybutanoyl chloride interact with Lewis acids to form either donor‐acceptor complexes or delocalized carbenium ions which can be characterized by 13C NMR spectroscopy. The chemical shift values are compared with shifts in model systems obtained by the protonation of glutaric anhydride, γ‐butyrolactone and δ‐valerolactone, and by the methylation of γ‐butyrolactone and δ‐valerolactone.
Proton and carbon‐13 NMR relaxation studies of 2,2‐dichloropropane and 2,2‐dibromopropane
Authors: Aksnes D. W. , Ramstad K.
Published: May 2005

Proton and 13C line widths and spin‐lattice relaxation times, T1, have been measured for liquid and solid 2,2‐dichloropropane (1) and 2,2‐dibromopropane (2). Molecular self‐diffusion, with activation energies in the range 18‐24 kJ mol−1, is responsible for the considerable line narrowing observed for the NMR spectra in solid I of these substances. The NMR data reveal a previously unreported phase transition point at 208 K for 2.

An analysis of the proton and 13C T1 times in both the liquid and solid phases is reported. Effective correlation times, activation energies and pre‐exponential factors for the appropriate motions have been obtained from the Arrhenius equation. The proton and 13C spin‐lattice relaxation mechanisms in the liquid and solid I phases are governed by overall molecular reorientations, with activation energies in the range 9–11 kJ mol−1. The rotational correlation time increases slightly at the liquid → solid I boundary from 3.2 to 3.6 ps for 1 and from 5.1 to 5.4 ps for 2. The correlation time is observed to decrease by five orders of magnitude at the solid I → solid II transition point of 2. The dominant motion causing spin‐lattice relaxation in phase II is methyl group reorientation with an activation energy of 18 kJ mol−1.
Indirect 1H19F1H and 1H19F13C nuclear overhauser enhancements: Anomalous intensity effects and applications in conformational analysis
Authors: Sánchez‐Ferrando Francisco , Sanders Jeremy K. M.
Published: May 2005

Indirect nuclear Overhauser enhancements through 19F have been determined for the three‐spin systems 1H‐19F‐1H and 1H‐19F‐13C by steady‐state presaturation of the appropriate proton, and applied to the conformational analysis of 5‐bromo‐2‐fluoro‐4‐nitroacetanilide. The 1H NOE difference spectra at 400 MHz showed antiphase doublets for protons undergoing simultaneous dipolar relaxation with, and scalar coupling to, 19F. Similarly, in the 13C selective NOE difference spectrum at 100 MHz, the two lines of the fluorine‐bearing carbon showed negative enhancement factors of different magnitude on presaturation of the appropriate proton. The use of these anomalous intensity effects in conformational analysis is illustrated.
13C chemical shifts of 1‐cyano‐para‐substituted 1,2‐diphenylcyclopropanes
Authors: Schanck AndréA , Deblock Isabelle , Van Meerssche Maurice , Leroy Georges , Weiler Josy
Published: May 2005

Fifteen 1 ‐cyano‐l,2‐diphenyl cyclopropane derivatives were analysed by 13C NMR spectroscopy. The chemical shifts for each carbon have been assigned.
Studies of intramolecular electronic effects in chloroacetophenones C6H5COCH3‐n Cln and p‐ClC6H4COCH3‐n Cln by 35Cl NQR
Authors: Nogaj Boleslaw , Schroeder Grzegorz
Published: May 2005

35Cl NQR (77 K) spectra for two groups of compounds, C6H5COCH3‐n Cln and p‐ClC6H4COCH3‐nCln, are reported. The frequencies were assigned to individual chlorine atoms in the molecules. Polar effects and mechanisms of conjugation in the molecules are discussed. The influence of the polar carbonyl group on the electronic structure of the molecule and the NQR frequency was studied in detail.
1D‐ and 2D‐NMR study of a nonapeptide, a fragment of collagen, in its free state and complexed with aluminium (III)
Authors: Gervais M. , Commenges G. , Laussac J.‐P.
Published: May 2005

1H NMR studies at 250 MHz and 13C NMR studies at 62.8 MHz on the synthetic nonapeptide fragment of type III collagen, Gly‐Lys‐Hyp‐Gly‐Glu‐Hyp‐Gly‐Pro‐Lys (CP9), have been carried out in aqueous solution and DMSO‐d6. The resonances are assigned with the help of 2D correlated spectroscopy, pH titrations by following the characteristic pK values exhibited by protons adjacent to ionization sites and one‐dimensional (1D) spin decoupling techniques. Chemical shifts of the proline and hydroxylproline carbon atoms indicate that the trans configuration about the three X—Pro and XHyp peptide bonds is strongly favoured in all cases, although the minor cis resonances accounting for about 10% of the Pro and Hyp intensity can also be observed. In addition, there appears to be no significant pH sensitivity of the cis ⇌ trans equilibrium. Addition of aluminium causes changes in the spectra, indicating specific interactions with carboxylates of the glutamyl and lysyl residues, as well as a change for both hydroxylproline residues. These data are interpreted by the formation of a 1:2 stoichiometric complex (AlIII‐CP9). the implication of these results with respect to the effect of aluminium in the tanning process is discussed.
Structural studies in the cedrane series by 13C NMR
Authors: Brun P. , Casanova J. , Raju Muppala S. , Waegell B. , Wenkert Ernest , Zahra J. P.
Published: May 2005

The complete analysis of the 13C NMR spectra of 30 cedrane derivatives with various functionalities on the 2, 6, 6, 8‐tetramethyltricyclo[5.3.11,701,5]undecane skeleton is reported. The assignment of the signals to the appropriate carbons has been made using the various functionalities on the molecular framework and the chemical shift theory (α, β, γ effects). When necessary, off‐resonance decoupling, INEPT and DEPT experiments have been used, as well as specific deuterium labelling. The last ambiguities were resolved with the aid of lanthanide shift reagents and SFORD experiments. The assignments for the reference compounds neoisocedranol oxide, cedrol and cedrene were made using the carbon‐carbon connectivity 2D INADEQUATE pulse sequence. The examination of cedrane derivatives functionalized on C‐9 (carbonyl, hydroxyl, acetate) and C‐8 (methyl, axial or equatorial) showed that the 13C chemical shifts of C‐5, ‐6, ‐11 and ‐13 are sensitive probes for the conformation of the six‐membered ring (ring C), which is essentially a flattened chair, and for the stereochemistry of the C‐8 and C‐9 substituents. Comparison with 2‐methylbicyclo[3.2.1]octan‐3‐ones shows that the Anti Reflex effect is operative in cedrane derivatives.

Cedrane oxides and their derivatives have also been examined and the corresponding 13C data are reported. Using all this information it was possible to carry out a complete analysis of lac acids, which have a functionalized tricyclo[5.31,7, 01,5]undecane framework like the cedrane derivatives. The 13C spectral analysis shows that, from the structural point of view, this tricyclic system behaves as a bicyclo[3.3.0] skeleton with an additional three‐carbon bridge between C‐1 and C‐7, rather than as a bicyclo[3.2.1]octane with an additional cyclopentane fused on C‐1 and C‐5; when additional strain is introduced into this system, the five‐membered ring A and the six‐membered ring C undergo conformational deformations more easily than ring B.
13C NMR spectra of eudesmanolides I—eudesman‐12,6‐olides
Authors: Marco J. A. , Carda M.
Published: May 2005

The 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

13C 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

The 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

The 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

It 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

A 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

Condensation 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

Carbon‐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

A 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

The 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

Cyclopropylmethyl 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

Metal(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

The 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

Pure 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

To 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

The 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

13C 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

Several 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

The 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

γgauche 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

The 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

Barriers 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

The 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

13C 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

The 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

1H 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

The 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

Two‐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

1H 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

The 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

The 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.
Spin density distribution in dialkyl oxalate radical anions
Authors: Brix P. , Helling D. , Voss J.
Published: May 2005

The isotropic and anisotropic ESR spectra of dialkyl oxalate radical anions, including derivatives which were labelled with 13C or 17O in the carbonyl and 2H or 13C in the alkyl groups, were measured. The spin density distribution as determined from the experimental nuclear hyperfine coupling constants agrees very well with MNDO‐CI calculations. As a consequence of the strictly planar structure of the radical anions, E/Z isomers are observed.
13C1H shift correlation with full 1h1H decoupling
Authors: Perpick‐Dumont Marion , Reynolds William F. , Enriquez Raul G.
Published: May 2005

A pulse sequence for obtaining 13C1H shift‐correlated spectra with full 1H1H decoupling is described and evaluated. It is concluded that the sequence provides excellent resolution, even for strongly coupled methylene groups. The sensitivity is superior to those of existing sequences based on 13C detection for organic compounds in the molecular weight range up to ca 500.
Study of disaccharide conformation by one‐and two‐dimensional NMR spectroscopy: 1,6‐anhydro‐β‐maltose hexaacetate
Authors: Dais Photis , Perlin Arthur S.
Published: May 2005

One‐ and two‐dimensional NMR spectroscopy were employed to determine the conformation of 2,3,4,6,2′,3′‐hexa‐O‐acetyl‐4‐O‐α‐D‐glucopyranosyl‐1′,6′‐anhydro‐β‐D‐glucopyranose in acetone‐d6 solution. Inter‐residue interproton distances, H‐1–H‐4′ and H‐1–H‐3′, determined by 2D NOE experiments are commensurate with torsional angles ϕ and Ψ of −10° and −20°, and also of 10° and −30°, about the inter‐residue glucosidic bond. Computer simulation showed that, within the limits of the experimental error (ca ±0.20 Å) of the interproton distances determined, several sets of ϕ and ψ angles are consistent with the NMR data. These ‘allowed’ conformations are presented in the form of a conformational map.
The stereochemistry of crown ethers. II —1H and 13C NMR structural study in solution
Authors: Kleinpeter E. , Gäbler M. , Schroth W. , Mattinen J. , Pihlaja K.
Published: May 2005

The 1H and 13C NMR spectra of a series of structurally related crown ethers have been recorded, and the signals assigned by means of 1H/13C heteronuclear correlated and 1H/1H homonuclear NOE difference spectroscopy. The NMR parameters so extracted have been used to discuss the preferred, rapidly interconverting solution conformations of the studied species. The high‐field shifts in the 13C NMR spectra, within the so‐called γ‐fragments, and also the 1H/1H homonuclear NOEs, are particularly informative in this respect. The T1 relaxation times of the 13C atoms show segmental motions within the ether segments and suggest different intramolecular flexibilities for the studied compounds.
EPR and ENDOR investigations of dynamic processes in sterically overcrowded phenoxyl‐type galvinoxyl radicals
Authors: Von Gersdorff J. , Kirste B. , Niethammer D. , Harrer W. , Kurreck H.
Published: May 2005

The syntheses of tert‐butylgalvinol with perdeuteriated tert‐butyl groups and of 1,4‐bicyclo[2.2.2]octanebisgalvinol are described. The EPR and ENDOR spectra of the corresponding galvinoxyl monoradicals reveal selective line broadening due to dynamic processes associated with hindered internal rotation of the phenoxy rings. Deuteriation of the central tert‐butyl group in tert‐butylgalvinoxyl gives rise to a substantial decrease of EPR line widths, allowing the determination of the kinetic parameters by means of line‐shape analyses (ΔH≠ = 21.8 kJ mol−1, ΔS≠ = −32 J mol−1 K−1). The biradical 1,4‐bicyclo[2.2.2]octanebisgalvinoxyl exhibits strong scalar and dipolar electron interactions (D = 97 MHz).
Repeatability and reproducibility of site‐specific isotope ratios in quantitative 2H NMR
Authors: Guillou C. , Trierweiler M. , Martin G. J.
Published: May 2005

The repeatability and reproducibility of quantitative deuterium NMR at the natural abundance have been determined according to the ISO norms in a collaborative study

This study was organized by the Community Bureau of Reference, EEC (Bruxelles). The list of the participants is given at the end.

involving 16 spectrometers.

A repeatability of better than 0.8% and a confidence interval of 0.25% have been determined from the results obtained in the 15 different European laboratories that participated in the collaborative study. The reproducibility of the measurements carried out on very different NMR systems is of the order of 2–3%, but this can be improved to 1% with more homogeneous spectrometer systems.

The influence of the spectrometer performances on the precision of the quantitative data has been analysed in terms of statistical inference, variance analysis and multidimensional factorial representation. The results indicate the advantages of using highly automated procedures to decrease the random error in the measurement.
Experimental test of karplus‐type relationships for 3J(Sn, C) and 3J(Sn, H)
Authors: Mitchell T. N. , Podesta J. C. , Ayala A. , Chopa A. B.
Published: May 2005

Multinuclear (1H, 13C, 119Sn) NMR data are presented for a series of compounds of the type XMe2SnCHRCHR'CO2Me (X = Me, Cl; R, R' = Me, Ph). Values of 3J(H, H), 3J(Sn, H) and 3J(Sn, C) were used to assign the preferred conformations of these compounds and at the same time to test the empirical relationships proposed previously for 3J(Sn, C) and (indirectly) 3J(Sn, H); the validity of these relationships was confirmed.
Compounds with bridgehead nitrogen. 56—The 1H NMR spectra and stereochemistry of some perhydrooxazolo[3,4‐a]quinolines and 3,3a,4,5‐tetrahydro‐1H‐oxazolo[3,4‐a]quinolines
Authors: Crabb Trevor A. , Heywood Geoffrey C.
Published: May 2005

The configurations and preferred conformations of some perhydrooxazolo[3,4‐a]quinolines and of the related 3,3a,4,5‐tetrahydro‐1H‐oxazolo[3,4‐a]quinolines have been assigned on the basis of their 1H NMR spectra. Comparison of the spectra of the two sets of compounds shows the effect of replacement of the alicyclic ring in the fully reduced compounds by the aromatic ring in the 3,3a,4,5‐tetrahydro‐1H‐oxazolo[3,4‐a]quinolines on the 1H NMR parameters of the NCH2O protons.
Carbon‐13 NMR study of 1‐(trifluoromethyl)‐dihydro‐ and ‐tetra‐hydro‐naphthalenes
Authors: Bonnet‐Delpon D. , Ourevitch M.
Published: May 2005

13C NMR data for variously functionalized and substituted 1‐CF3‐tetrahydronaphthalenes are reported. A complete assignment of the chemical shifts has been achieved.
13C NMR spectroscopic study of the rearrangement of 16β‐hydroxy‐17‐oxo steroids to 17β‐hydroxy‐16‐oxo isomers
Authors: Doller Darío , Gros Eduardo G.
Published: May 2005

The acid‐catalysed rearrangement of 3β, 16β‐dihydroxyandrost‐5‐en‐17‐one to 3β, 17β‐dihydroxyandrost‐5‐en‐16‐one was studied by 13C NMR spectroscopy. The spectra indicated that the reaction is produced by an intramolecular 1, 2‐shift of hydride from C‐16α to C‐17α.
Long‐range CH correlation 2D NMR spectroscopy. 4—Complete spectral assignments of the pesticide metabolite S‐(2,3‐dihydroxy‐1‐propyl)glutathione
Authors: Krishnamurthy V. V. , Casida John E. , Dohn David R.
Published: May 2005

Complete 13C and 1H spectral peak assignments of S‐(2,3‐dihydroxy‐1‐propyl)glutathione (1) (an in vivo metabolite of the pesticide 1,2‐dibromo‐3‐chloropropane) were made using various 2D NMR techniques. Long‐range CH correlation 2D NMR unambiguously assigned the key methylene resonances adjacent to sulfur. Appropriate delays for optimum cross‐peak intensities in the long‐range correlation experiment were chosen with response intensity curves, generated using estimated long‐range coupling constants. These curves, although generated assuming a first‐order coupling network, are useful even in systems with strong second‐order couplings as in 1.
Generation of quinone cation radicals via photo‐induced electron transfer: ESR evidence
Authors: Liu Zhong‐Li , Wu Lung‐Min , Liu You‐Cheng
Published: May 2005

Benzoquinone cation radicals of 1,4‐benzoquinone and methyl‐, 2,5‐dimethyl‐ and 2,6‐dimethyl‐1,4‐benzoquinone were formed from the corresponding parent quinones by in situ UV photolysis in trifluoroacetic acid at ambient temperature, and detected by ESR. The cationic character of the radical species was confirmed by the electron transfer between the quinone cation radicals and N,N,Ń,Ń‐tetramethyl‐p‐phenylenediamine (TMPD). In the case of tert‐butyl substituted benzoquinones, instead of the corresponding cation radicals, cyclized radicals, i.e. the 3,3‐dimethylcoumaran‐5‐oxy and 3,3‐dimethyl‐7‐tert‐butylcoumaran‐5‐oxy radicals and the 3,3‐dimethyl‐6‐tert‐butylcoumaran‐5‐hydroxy cation radical were detected from tert‐butyl, 2,6‐di‐tert‐butyl‐ and 2,5‐di‐tert‐butyl‐1,4‐benzoquinones, respectively. A mechanism involving electron transfer between the photoexcited quinone and that in the ground state is proposed.
Chirality in hindered naphthylamines
Authors: Herbst Thomas , Schiemenz Günter P. , Wolff Christian
Published: May 2005

peri‐Substituted ethylmethyl‐1‐naphthylamines were shown by means of 1H and 13C NMR spectroscopy to be chiral at and above room temperature.
Aromatic substituent chemical shifts and J(CF) coupling constants in fluoro‐substituted benzenes
Authors: Newmark Richard A. , Hill James R. , Tiers George V. D.
Published: May 2005

Aromatic substituent chemical shifts are reported for the difluoromethylthio, trifluoromethoxy, pentadecafluoroheptyl and fluosulfonyl groups. Long‐range coupling to the ortho and para carbons is observed in all cases except the trifluoromethoxy group.
Microcomputer simulation of solid‐state 13C NMR line shapes affected by quadrupolar nuclei
Authors: Olivieri Alejandro , Frydman Lucio , Grasselli Mariano , Diaz Luis
Published: May 2005

Solid‐state 13C NMR spectra of 14N‐containing compounds obtained under CPMAS conditions often show asymmetric doublets arising from the unaveraged 13C,14N residual dipolar coupling. A similar result has recently been noticed in deuteriated samples, whose 13C resonances showed the combined effect of 13C,2H dipolar and scalar couplings. A simple approach, easily adaptable to a desk microcomputer, is described for simulating 13C line shapes for arbitrary values of quadrupole parameters, CX (X = 14N, 2H) distances, external field and orientation of the internuclear vector in the axis system where the electric field gradient tensor is diagonal.
Solubilization of aromatics in aqueous bile salts. IV—Two‐dimensional 1H NMR study on intra‐ and inter‐molecular interactions in aromatic solubilizate–cholate systems
Authors: Kolehmainen E.
Published: May 2005

Solubilization of aromatics in aqueous bile salts was studied by two‐dimensional (2D) nuclear Overhauser enhancement spectroscopy (NOESY) for three model systems: benzene, anisole and veratrole solubilized in aqueous sodium cholate. The observed intra‐ and inter‐molecular cross‐relaxation properties are discussed in terms of different solubilization sites available for different solubilizates. The cholate anions located in the micelles seem to maintain their intramolecular cross‐relaxation characteristics during the mixed micelle formation. A molecular mechanical calculation of the cholate anion was performed in order to determine the non‐bonded internuclear distances between the NOE‐connected nuclei.
Complete assignment of the 13C NMR spectra of bleomycin A2 and its zinc complex by means of two‐dimensional NMR spectroscopy
Authors: Akkerman M. A. J. , Haasnoot C. A. G. , Pandit U. K. , Hilbers C. W.
Published: May 2005

13C NMR spectra of free bleomycin A2 at pH 4 and 6.7 and of its zinc complex at pH 6.7 were completely assigned by making use of two‐dimensional 1H13C correlated spectroscopy. Differences in resonance positions between the spectra of the free bleomycin at pH 4 and 6.7 are observed for the β‐hydroxyhistidine and the β‐aminoalanine residues, obviously because of protonation/deprotonation of these moieties in the pH region considered. Also, shifts are observed for the carbon resonances of the gulose residue. Upon complex formation between zinc(II) and bleomycin large 13C shifts are observed for the carbon atoms in the pyrimidinepropionamide, β‐hydroxyhistidine, β‐aminoalanine, α‐L‐gulose and α‐D‐mannose fragments. Although for some residues the observed shifts correspond with the position of the zinc(II) binding sites in bleomycin proposed on the basis of earlier 1H NMR experiments, a simple correlation between the location of the zinc(II) binding sites and the 13C shifts cannot be drawn.
Two‐dimensional6Li,1H heteronuclear Overhauser spectroscopy (HOESY) in magnitude and pure absorption representations. Application to a dimer–monomer equilibrium of a 1,4‐dilithio compound
Authors: Bauer Walter , Schleyer Paul Von Ragué
Published: May 2005

6Li,1H HOESY was used both for the detection of short lithium–proton distances and for proton spectral assignments of 1,8‐dilithio‐1,2‐diphenylhex‐1‐ene, which exists as a monomer–dimer equilibrium mixture in tetrahydrofuran (THF‐d8). Experiments using magnitude mode, pure absorption and pseudo‐steady‐state mode representations are described. Pure absorption6Li,1H HOESY proved to be the superior method.
Total assignment of the 1H‐ and 13C‐NMR spectra of dinaphtho[1,2‐b:1′,2′‐d]thiophene through the concerted use of two‐dimensional NMR techniques
Authors: Johnston Milton D. , Castle Raymond N. , Salazar Miguel , Kruger Diana K. , Martin Gary E.
Published: May 2005

The 1H‐ and 13C‐NMR spectra of dinaphtho[1,2‐b:1′2′‐d]thiophene (1), a sulfur‐containing polynuclear heteroaromatic, have been totally assigned using a combination of two‐dimensional NMR techniques. Techniques applied were standard proton‐proton COSY, proton zero‐quantum coherence (ZQCOSY, optimized to 7 Hz and to 1.75 Hz), proton double quantum coherence (DQCOSY, optimized to 7 Hz), broad‐band decoupled (both dimensions) proton‐carbon chemical shift correlation, long‐range proton‐carbon chemical shift correlation, and proton‐carbon heteronuclear relayed coherence transfer. A comparison of these methods on 1 showed the most useful information concerning connectivities to be obtained from the zero‐quantum coherence and long‐range heteronuclear correlation experiments. A detailed critique of each type of experiment is given in the context of applications to polynuclear aromatics.
Extraction of 1H1H and 1H13C dipolar couplings from spectra acquired in inhomogeneous magnetic fields
Authors: Kay Lewis E. , Thomson D. S. , Prestegard J. H.
Published: May 2005

Experimental procedures are presented for the extraction of 1H1H and 1H13C dipolar couplings from molecules oriented in high magnetic fields without a requirement for high field homogeneity. These couplings impose restrictions on structure in a manner similar to NOE distances and can serve as useful additional constraints for defining structure. The experimental procedures involve pulse sequences which refocus the effects of magnetic field inhomogeneities but which retain dipolar couplings, scalar couplings and, in cases of chemically distinct groups, chemical shift differences. The methods are important for the extension of experiments to higher fields and more complex media where field homogeneity is hard to maintain. The experiments are illustrated using samples containing sodium acetate‐99% 13C2 or alanine‐99% 13C3 dissolved in a nematic liquid crystal and oriented in an inhomogeneous magnetic field. Coupling constants obtained from the studies are in good agreement with couplings extracted from one‐dimensional spectra obtained in homogeneous fields.
Indirect two‐dimensional heteronuclear NMR spectroscopy of low‐γ metal nuclei (M = 183W, 57Fe, 103Rh, 61Ni)
Authors: Benn Reinhard , Rufińska Anna
Published: May 2005

Indirect two‐dimensional (X, M) (X = 1H, 31P) triple resonance spectroscopy is presented for the detection of the NMR parameters of insensitive metal nuclei M = 57Fe, 103Rh, 183W and 61Ni which exhibit a scalar coupling to the more sensitive X nucleus. The versatlity of this approach is demonstrated and compared with the previously used detection schemes by recording δ(M) and J(M, X) for a series of organometallic phosphorus tungsten(IV), rhodium(I), iron(0), iron(II) and nickel(0) complexes. The NMR data of the complexes are discussed.