bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear magnetic resonance imaging as a probe of the freezing—thawing phenomena of liquids in heterogeneous systems
Authors: Fyfe Colin A. , Isbell Stephanie A. , Burlinson Nicolas E.
Published: May 2005

NMR microscopic imaging is shown to be an excellent probe of the freezing and thawing phenomena of liquids in heterogeneous chemical systems, and, in addition, is capable of monitoring the freezing‐thawing of mixed solvent systems. In the model mixed solvent system Me2SO–water, the chemical shift specific slice selective (C4S) imaging technique is used to obtain the spatial distributions of the concentrations and mobilities of the two individual solvents in test samples. Measurements of relaxation parameters make it possible to choose values of imaging parameters TE and TR to ensure quantitative reliability of the images. Images of test samples generated at various temperatures demonstrate the qualitative relationship between image intensity and the Me2SO–water phase diagram. This series of experiments verifies that NMR microscopic imaging will be a powerful tool for the study of liquids within solid matrices, and in particular of cryoprotectant solvents in biological systems.
Deuterium isotope effects as evidence for substituent perturbation of the π‐electron frame in benzanilides
Authors: Morales‐Ríos Martha S. , Pérez‐Alvarez Víctor , Joseph‐Nathan Pedro , Zepeda L. Gerardo
Published: May 2005

Deuterium isotope effects on 13C nuclear shielding, nΔC(D), transmitted across a D‐labelled nitrogen atom were investigated for a series of para‐substituted benzanilides. The two two‐bond isotope shifts, 2ΔC(D) are perturbed essentially in a trough‐bond manner by change of the contribution of mesomeric structures. The magnitudes of 2Δ(CO) and 2Δ(C‐1′) are found to be mutually interdependent as evidenced by the linear relationships between the average values of 2Δ(CO) and 2Δ(C‐1′) with 1H(NH) chemical shifts and with 15N SCS. This behaviour is interpreted as resulting from a cross‐conjugated transmission pathway involving the carbons sharing the D‐labelled nitrogen.
Carbon‐13 NMR studies on azolopyridines. 3—the isothiazolopyridine systems
Authors: Chimichi Stefano , Cosimelli Barbara , Tedeschi Piero , Ponticelli Fabio
Published: May 2005

All four fully aromatic isothiazolopyridine isomers have been synthesized, their 13C spectra have been assigned and all one‐bond and long‐range 13C1H coupling constants have been determined.
17O NMR spectra of vinyl ethers
Authors: Taskinen Esko , Hellman Jaakko
Published: May 2005

The 17O NMR spectra of 58 α,β‐unsaturated (vinyl) ethers were recorded in CDCl3 solution. The dependence of the chemical shift on the number and position of alkyl substituents in the vinyl moiety and on the nature and bulkiness of the alkoxy group was explored. The oxygen chemical shifts proved to be sufficiently sensitive to structural factors to make 17O NMR spectroscopy a useful tool in the investigation of the electronic and spatial structures of vinyl ethers.
Simple technique for temperature calibration of a MAS probe for solid‐state NMR spectroscopy
Authors: Aliev Abil E. , Harris Kenneth D. M.
Published: May 2005

A simple method is reported for temperature calibration of a magic angle spinning probe for solid‐state NMR spectroscopy. The method is an extension of that developed by van Geet for temperature calibration of liquid‐state NMR probes, and consists of measuring the frequency difference (Δν) between the resonances for the methyl and hydroxyl protons of methanol in the 1H NMR spectrum of a sample of tetrakis(trimethylsilyl)silane soaked in liquid methanol. The successful application of this method for temperature calibration was demonstrated from an assessment, from high‐resolution solid‐state 13C NMR spectroscopy, of the phase transition temperatures for solid tetrakis(trimethylsilyl)silane and for solid 2,2‐dimethylpropane‐1,3‐diol.
13C NMR spectroscopic data for glutinol and derivatives
Authors: Olea Roberto Sigfrido Gallegos , Torres Luce Maria Brandão , Roque Luiz Carlos , Roque Nidia Franca
Published: May 2005

The 13C NMR chemical shifts of the triterpenes glutinol, glutinone and acetylglutinol were measured and analysed.
Steric effects induced by solvent association. 29Si NMR chemical shifts in trimethylsiloxysteroids controlled by solvent accessible surface
Authors: Kasal A. , Schraml J. , Čermák J.
Published: May 2005

Chemical shifts of silicon‐29 in 39 trimethylsiloxy derivatives of 5α‐ and 5β‐androstanes reported here satisfy an empirical linear correlation with terms describing molecular geometry. The steric 29Si chemical shifts are controlled by association of the silyl ethers with the hydrogen bonding solvent. The chemical shifts measured in dilute solutions show a dependence on the surface of the oxygen atom accessible to the solvent for hydrogen bonding. The steric upfield shifts are due to steric hindrance to hydrogen bonding which itself produces downfield shifts.
Diamagnetic lanthanide tris‐β‐diketonates as ‘dissolving’ reagents
Authors: Komarov Igor V. , Kornilov Mikhail Yu. , Turov Aleksandr V.
Published: May 2005

It is proposed to use diamagnetic lanthanide tris‐β‐diketonates as auxilliary reagents to promote solubilization of organic compounds in low‐polarity solvents, thereby enhancing the NMR spectral sensitivity. For such a purpose the lanthanum complexes with fluorinated β‐diketonate ligands were shown to be the most suitable. These tris‐β‐diketonates form adducts with compounds possessing ‘hard’ Lewis base functional groups, and the adducts are more soluble than their components. The effect of the lanthanum complexes on paramagnetic shifts induced by lanthanide shift reagents was examined. A considerable increase in the shifts values was found in the presence of some lanthanum tris‐β‐diketonates.
Substituted methyl 5β‐cholan‐24‐oates. I—17O NMR spectral characterization
Authors: Kolehmainen Erkki , Kaartinen Mari , Kauppinen Reijo , Kotoneva Jari , Lappalainen Kari , Lewis Philip T. , Seppälä Raimo , Sundelin Jukka , Vatanen Virpi
Published: May 2005

Methyl esters of four common bile acids, 3α‐hydroxy‐5‐β‐cholan‐24‐oic (lithocholic) acid, 3α, 7α‐dihydroxy‐5β‐cholan‐24‐oic (chenodeoxycholic) acid, 3α,12α‐dihydroxy‐5β‐cholan‐24‐oic (deoxycholic) acid and 3α,7α,12α‐trihydroxy‐5β‐cholan‐24‐oic (cholic) acid, and 14 acetylated, trifluoroacetylated, mesylated and oxo derivatives of methyl 5β‐cholan‐24‐oates were prepared and their 17O NMR spectra recorded. In spite of their relatively high molecular masses and the rigid molecular structure of the steroid skeleton, most of the oxygens included in these structures gave well resolved 17O NMR resonance lines at natural abundance in 0.25–0.5 M acetonitrile solutions at 75°C. In agreement with the present 17O NMR results, molecular mechanics calculations revealed that a hydroxy substituent located at the 3α‐position clearly differs from the hydroxyls at the 7α‐ and 12α‐positions. This is due to the fact that the 3α‐hydroxyl possessing only two γ‐carbons at antiperiplanar positions is less shielded than the other hydroxyls influenced also by the shielding effects of γ‐gauche carbons. The spectral deconvolution of the overlapping signals of the 7α‐ and 12α‐hydroxyls is based on a computer‐aided method or on chemical substitutions. The oxo groups located at the longitudinal (3‐oxo) vs. transversal (7‐ and 12‐oxo) axes of the steroid framework show very different quadrupolar relaxation properties and 17O NMR linewidths owing to the strong anisotropy of overall molecular motion. In contrast, the 17O NMR linewidths of all 3α‐, 7α‐ and 12α‐hydroxyls are very similar and clearly smaller than those of the corresponding oxo groups, revealing that their quadrupolar relaxation is merely determined by their internal rotation rather than by the overall molecular motion.
1H and 13C NMR studies of the self‐association of chlorpromazine hydrochloride in aqueous solution
Authors: Attwood David , Waigh Roger , Blundell Ross , Bloor Debra , Thévand André , Boitard Elizabeth , Dubès Jean‐Paul , Tachoire Henri
Published: May 2005

The 1H NMR spectrum of chlorpromazine hydrochloride was fully assigned at 400 MHz. Similarly, the 13C NMR spectrum was assigned unambiguously using two‐dimensional NMR. Measurements of chemical shift as a function of concentration in D2O showed appreciable changes of shift of both protons and carbons which were apparent even at solution concentrations two orders of magnitude lower than the critical micelle concentration (CMC). The relative magnitude of the shifts of the aromatic protons and carbons on dilution below the CMC were compatible with vertical stacking of the molecules in an off‐set manner such that maximum overlap of the chlorinated rings occurred. Proton chemical shift data were interpreted using a stepwise association model to quantify the extent of association in the pre‐CMC region.
ESR spectra of 4‐phenyl‐1,2,3,5‐diselenadiazolyl, PhCN2Se2·, and the first diselenadiazolyl metal complex, Pt[PhCN2Se2][PPh3]2
Authors: Rawson Jeremy M. , Banister Arthur J. , May Iain
Published: May 2005

Anisotropic ESR spectra (THF, frozen glass, 77 K) of PhCN2Se2˙ provide valuable information about the electronic structure of the diselenadiazolyl radical. Reaction of PhCN2Se2˙ with Pt(PPh3)3 in CH2Cl2 yielded the first diselenadiazolyl–metal complex, Pt[PhCN2Se2][PPh3]2. The electronic structures of both compounds are described in comparison with their sulphur analogues and the isoelectronic SN2E2+˙ radicals (E = S, Se).
Variable‐temperature and pH studies of a DNA minor groove binder, Hoechst 32985, by 1H NMR spectroscopy
Authors: Cross Keith J. , Embrey Kevin J. , Coles Murray , Bicknell Wendy , Craik David J.
Published: May 2005

1H NMR spectra of the dipiperazine‐based DNA minor groove binding compound Hoechst 32985 indicate that at room temperature and low pH (2.90) a single conformation is detected. This is attributed to the form in which both piperazine rings are protonated at the N‐methyl and the bulky methyl and aromatic groups are in an equatorial arrangement. The aliphatic regions of the spectra broaden considerably with an increase in either temperature or pH, indicating the presence of a dynamic exchange process. This process results in interchange of axial and equatorial environments of the piperazine ring protons and is attributed to combined ring and nitrogen inversions. Analysis of the variable‐temperature spectra for a solution at pH 2.90 allowed a Gibb's free energy of activation (ΔG‡) of 69.4±0.4 kJ mol−1 to be calculated for this process.
13C and 19F NMR spectra of a series of laterally fluorinated mesogens
Authors: Loubser Christa
Published: May 2005

13C and 19F NMR spectra of a series of mesogenic compounds, (S)‐4‐n‐octyloxy‐fluorobiphenyl‐4′‐yl fluoro‐4‐(2‐fluoro‐octanoyloxy)benzoates, were determined in solution. The effect of fluoro substitution in various positions on the 13C and 19F chemical shifts was studied. 13C, 19F and 19F, 19F scalar coupling constants are given.
Complete assignment of the 1H and 13C NMR spectra of deoxyhemigossypol derivatives
Authors: Alam T. M. , Rosay M. , Deck L. , Royer R.
Published: May 2005

The 1H and 13C NMR spectra of the deoxyhemigossypol derivatives 4‐isopropyl‐2,3‐dimethoxy‐6‐methylnaphthalene, 4‐isopropyl‐2,3‐dimethoxy‐6‐methyl‐1‐naphthaldehyde and 2,3‐dihydroxy‐4‐isopropyl‐6‐methyl‐1‐naphthaldehyde were assigned using one‐ and two‐dimensional NMR techniques, including DEPT, 1H NOE and 1H13C HETCORR spectroscopy.
Carbon‐13 NMR data for methylated steroids
Authors: Meskó E. , Schneider Gy. , Dombi Gy. , Zeigan D.
Published: May 2005

Carbon‐13 chemical shifts of 40 methylated steroid derivatives are reported.
Proton and carbon‐13 NMR and conformation in solution of some amorphanes (quinghaosu derivatives)
Authors: Marsaioli Anita J. , Fujiwara Fred Y. , Foglio Mary Ann , Sharapin Nikolai , Zhang Jin‐Sheng
Published: May 2005

The total proton and carbon‐13 NMR assignments of quinghaosu I, II and V isolated from Artemisia annua cultivated in Brazil and of the synthetic derivatives quinghaosu alkene, ketone and epoxy are reported. The conformations and conformational equilibria of these compounds in solution were obtained from the spectral data and molecular mechanics calculations.
13C NMR chemical shifts of heterocycles. Empirical substituent effects in 5‐halomethyl‐5‐hydroxy‐4,5‐dihydroisoxazoles
Authors: Martins Marcos A. P. , Martins Anna C. L.
Published: May 2005

Evaluation by empirically derived equations for the substituent effect (α, β, γ, δ) on the 13C NMR chemical shifts for C‐3, C‐4, C‐5 and halomethyl‐substituent carbon (C‐6) in 5‐halomethyl‐5‐hydroxy‐4,5‐dihydroisoxazoles (where C‐3 substituent=H), alkyl or phenyl, C‐4 substituent=H, alkyl or heteroalkyl and C‐5 substituent (=dior trihalomethyl), taking as reference 5‐trichloromethyl‐5‐hydroxy‐4,5‐dihydroisoxazole, is reported. From the calculated values for the α, β, γ and δ effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds.
Study of halogen exchange in allyltin trihalides by two‐dimensional 119Sn EXSY NMR
Authors: Pianet Isabelle , Fouquet Eric , Pereyre Michel , Gielen Marcel , Kayser François , Biesemans Monique , Willem Rudolph
Published: May 2005

(2‐Ethoxycarbonyl)crotylbromodichlorostannane (1) and (2‐ethoxycarbonyl)allylbromodichlorostannane (2), two compounds with formula RSnCl2Br, were shown by 2D phase‐sensitive EXSY 119Sn NMR to undergo halogen exchange, resulting in equilibrium mixtures of RSnCl3, RSnCl2Br, RSnClBr2 and RSnBr3. The unidirectional pseudo‐first‐order rate constants were determined by two different methods, the initial rate and the exchange matrix resolution approaches. The data show that the exchange proceeds by single halogen exchange, probably occurring through an intermediate involving two organotin trihalide moieties, as evidenced from the linear dependence of the pseudo‐first‐order rate constants on concentration. The mechanism is briefly discussed.
Restricted rotation of the phenyl group in β‐hydroxyphosphonates: Dynamic NMR and semiempirical studies
Authors: Vassilev Nikolay G. , Dimitrov Valentin S.
Published: May 2005

Free energies of activation, ΔG, for the rotation of the phenyl group in the range of 46.06–63.25 kJ mol−1 were observed in some model β‐hydroxyphosphonates. These barriers were found to depend on the type of substituents at the phosphorus atom and on the substituents at the β‐position with respect to the phenyl ring. The steric origin of this observation is discussed. Dynamic NMR studies were performed in order to determine the activation parameters for the exchange process. For that purpose, variable‐temperature 1H and 13C NMR spectra were treated by non‐iterative, iterative and iterative double‐fit procedures. MNDO, AM1 and PM3 theoretical calculations of the barriers for three of the compounds studied are reported and results are compared with the experiments. It is found that the PM3 results are very close to the experimental data.
Nuclear magnetic resonance spectral analysis of three isomeric 2,3,5‐trisubstituted N‐methylpiperidines
Authors: Kotzamani Heleni K. , Stamos Ioannis K.
Published: May 2005

The 1H and 13C NMR spectra of three stereoisomeric 2‐(p‐chlorophenylthiomethyl)‐3‐(3‐methoxyphenyl)‐5‐carbomethoxy‐N‐methylpiperidines were analysed in terms of configuration and solute conformation. These studies together with 2D J‐resolved, 2D‐COSY and 2D 1H13C‐correlated spectra demonstrate the existence of 2a‐3a‐5e, 2e‐3a‐5e and 2e‐3e‐5e chair conformations
Effect of hydroxyl and carbonyl groups on long‐range proton—carbon coupling constants
Authors: Parella Teodor , Sánchez‐Ferrando Francisco , Virgili Albert
Published: May 2005

Long‐range 1H13C coupling constants were measured for some simple, rigid model compounds containing hydroxyl, bromine or carbonyl groups. These were performed using the recently proposed selective J‐resolved SPININEP and SDEPT‐2D experiments. The geminal and vicinal heteronuclear coupling constant values were analysed in terms of the nature of substituent, the position along the coupling path and the orientation of the substituent relative to the bounds. In some cases, through‐space interactions of the substituent group were also observed. Sizeable substituent effects are associated with the electronegativity and lone pair of the oxygen nucleus in the hydroxyl and carbonyl systems. In addition, the π‐system of the carbonyl group may also be important. Such substituent effects may be as large at ±5 Hz. Since nJCH constants rarely exceed 10 Hz, these effects can produce important deviations in nJCH magnitudes and therefore are essential for applications to stereochemical and conformational analysis.
Molecular symmetry and shielding tensor properties—some illustrative examples
Authors: Klaus Elke , Sebald Angelika
Published: May 2005

13C, 29Si, 119Sn and 207Pb cross‐polarization magic angle spinning (CP/MAS) spectra for a series of closely related compounds R4−nM(CCR′)n, (n = 1−4; M = Si, Sn, Pb; R = alkyl; R′ = alkyl, SiMe3) are reported. Shielding tensor components for 29Si, 119Sn and 207Pb as obtained from CP/MAS spectra are discussed in relation to the respective highest possible molecular symmetry group as a function of the degree of substitution n = 1−4. For this class of compounds the orientation of the shielding tensor of M within the molecular frame can sometimes be derived from symmetry considerations. The limitations of such considerations, based on shielding tensor components obtained from polycrystalline powder samples under CP/MAS conditions, are discussed.
13C NMR chemical shift assignments of N‐monosubstituted and N,N‐disubstituted 3‐aminopyrroles
Authors: Rolfs Andreas , Mügge Clemens , Liebscher Jürgen
Published: May 2005

13C NMR chemical shift assignments of 47 N‐mono‐ and N,N‐disubstituted 3‐aminopyrroles with hydrogen or methyl in the 5‐position are reported. Substituents in the 2‐position are electron withdrawing such as alkoxycarbonyl, cyano or acyl in most cases and those in the 4‐position are aryl or ethoxycarbonyl.
Substituted methyl 5β‐cholan‐24‐oates II. 13C NMR spectral assignment
Authors: Lappalainen Kari , Kolehmainen Erkki , Kaartinen Mari , Kauppinen Reijo , Seppälä Raimo , Vatanen Virpi
Published: May 2005

The 13C NMR spectra were recorded and assigned for nine derivatives of methyl 5β‐cholan‐24‐oates (esters of bile acids) including hydroxy, oxo and/or acetyloxy groups. Assignments were based on the empirical substituent‐induced chemical shifts (SCS), spectral comparison with compounds of similar structure, distortionless enhancement by polarization transfer (DEPT) and proton coupled 13C NMR measurements.
1H NMR chiral analysis of benzhydrylamine derivatives using β‐cyclodextrin. Solution geometry of host‐guest complexes as determined by 1D NOE and ROESY experiments
Authors: Redondo J. , Frigola J. , Torrens A. , Lupón P.
Published: May 2005

The 1H NMR chiral analysis of a series of benzhydrylamine derivatives was accomplished by means of β‐cyclodextrin as chiral resolving agent, forming the corresponding inclusion complexes in aqueous solution. NOE and ROESY experiments were used in order to establish the most probable host‐guest geometries in solution. In all cases studied, it was found that the phenyl groups of guest molecules preferably binds with the macrocyclic cavity of β‐cyclodextrin, thus forming ternary complexes (2:1, β‐cyclodextrin:guest) when two phenyl groups were present in the guest molecule.
Approach to the conformational behaviour of tetraazamacrocycles in the solution state. NMR and molecular modelling studies
Authors: Boetzel R. , Failla S. , Finocchiaro P. , Hägele G.
Published: May 2005

The differences in complexation behaviour of two diastereomeric tetraazamacrocycles, meso (1) and racemic (2) 5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane, are explained by different conformations in solution, 1 being one stable conformer of almost rigid structure while 2 shows higher conformational flexibility to avoid steric strain. The methods used were 1H and 13C NMR and molecular modelling.
Use of cross‐polarization in lithium‐6 solid‐state NMR
Authors: Harris Robin K. , Minoja Anna P.
Published: May 2005

Cross‐polarization (CP) magic angle spinning (MAS) 6Li{1H} spectra were acquired for three different inorganic lithium compounds. Spectra with a good signal‐to‐noise ratio can be obtained in reasonable times. The poorer signal‐to‐noise ratios shown by spectra acquired in the same experimental time by means of a single pulse experiment are explained by the longer values of T1(6Li) in comparison with T1(1H). The determination of these values allows the acquisition parameters to be optimized. In particular, the optimum experimental conditions are discussed, taking into account the pulse delay, the number of transients and the total time of the experiment. Finally, a standard for 6Li1H CP matching is proposed.
19F NMR investigations of cobalt(II) complexes with cysteine‐containing peptide ligands
Authors: Sun Wei‐Yin , Ueno Takafumi , Ueyama Norikazu , Nakamura Akira
Published: May 2005

Isotropically shifted 19F NMR signals were observed for novel mononuclear Co(II) complexes, (Et4N)2[Co(Z‐Cys‐Pro‐Leu‐Cys‐Gly‐X)2] (Z = benzyloxycarbonyl, X = NHC6H4‐p = F, NHC6H4‐m‐F and NHCH2CH2C6H4‐p‐F). Such isotropically shifted signals show very short 19F spin‐lattice relaxation times (T1) in the range 20–150 ms compared with the corresponding SH‐free peptide ligands, Z‐Cys(SH)‐Pro‐Leu‐Cys(SH)‐Gly‐X, which revealed signals with 19F T1 values in the range 1600–3200 ms. The observed 19F NMR isotropic shifts and short 19F T1 values in the Co(II)‐cysteine‐peptide complexes are ascribed to the formation of NH—S hydrogen bonds and the presence of interactions of aromatic groups with the sulphur atom of the coordinated cysteine residue.
Complete spin dynamics of the AX, AX2 and AX3 spin systems. Application to BIRD pulses
Authors: Bain Alex D. , Burton Ian W. , Carpenter Katharine A. , Yang Ji‐Ping , Reynolds William F.
Published: May 2005

The BIRD pulse sequence is widely used to distinguish between protons that are directly bonded to a 13C nucleus and those that are not. It consists of a proton 90° pulse, a delay of 1/(21JCH), simultaneous carbon and proton 180° pulses, a further delay of 1/2J and a final proton 90° pulse. For two spins at equilibrium, the effect of this sequence can be easily understood, but for complex systems the behaviour can be counter‐intuitive. This paper explains the general behaviour of the BIRD sequence using theoretical equations and numerical simulations, and discusses some practical applications of the BIRD pulse train. The theoretical equations are derived using tables of general behaviour for the spin systems AX, AX2 and AX3. The tables allow the exact calculation of the effect of any pulse sequence on these spin systems, including all multiple quantum effects. The simulations show that the sequence is usually robust with respect to pulse imperfections and non‐ideal spin systems. In other cases, particularly when signals should be suppressed, small errors can have dramatic consequences. The results derived here are for a BIRD sequence inserted into an INEPT experiment, but many of the conclusions can be applied to all of the more standard applications of the BIRD.
Two‐dimensional 1H1H and 13C1H maximum‐quantum correlation NMR spectroscopy with application to the assignment of the NMR spectra of the bile salt sodium taurocholate
Authors: Liu Maili , Farrant R. Duncan , Lindon John C. , Nicholson Jeremy K.
Published: May 2005

Following earlier studies on the development of one‐ and two‐dimensional NMR methods based on selection of coherences via maximum‐quantum pathways and using inverse 1H detection, a pulse sequence is now described for analogous direct heteronuclear detection for use in laboratories which do not have access to inverse detection technology. The method has been applied to the assignment of all of the 1H and 13C NMR resonances of sodium taurocholate, an important component of bile. The assignment of the resonances of major bile salts is important for the assignments of NMR resonances in bile itself to yield understanding of altered biochemistry in disease states. The effect of deliberately missetting the refocusing delay in the pulse sequence is shown to be beneficial in the assignment process.
1H and 13C NMR spectra of spiramycin I in organic and aqueous solutions
Authors: Alam Perwaiz , Barber Jill , Brennan Richard J. , Kennedy Karen , Tehrani M. Hassan H.
Published: May 2005

Full assignments of the 1H and 13C NMR spectra of spiramycin l in CDCl3 and buffered D2O were carried out unambiguously using a range of 1D and 2D NMR methods.
Assignment of the 1H NMR resonances of D‐glycero‐D‐ido‐ and D‐glycero‐D‐altro‐octulose mono‐ and bisphosphates
Authors: Flanigan Ian L. , Collins J. Grant , Graham Kirstin L. , Macleod John K. , Williams John F.
Published: May 2005

The 1H NMR chemical shifts of the various contributing forms of the mono‐ and bisphosphates of D‐glycero‐D‐ido‐ and D‐glycero‐D‐altro‐octuloses were determined by two‐dimensional NMR spectroscopy.
17O NMR study of p‐π conjugation in methoxybutadienes and related compounds
Authors: Taskinen Esko
Published: May 2005

The 17O NMR spectra of some monomethoxy and dimethoxy derivatives of buta‐1,3‐diene, hexa‐2,4‐diene, cyclohexa‐1,3‐diene and cyclohexa‐1,4‐diene were recorded in CDCl3. The δ(17O) values show that in 2‐methoxybuta‐1,3‐diene the efficiency of p‐π conjugation in the OCC moeity is significantly lowered by cross‐conjugation of the CC bond with the other olefinic linkage. In the related system of 2‐methoxycyclohexa‐1,3‐diene, however, the corresponding effect is much smaller, apparently because of weak conjugative π‐π interaction in the olefinic system. On the other hand, the strength of p‐π conjugation appears to be the same in the OCCCC moieties of both 1‐methoxybuta‐1,3‐diene and 1‐methoxycyclohexa‐1,3‐diene. Moreover, as a transmitter of substituent effects, the unsaturated system of cyclohexa‐1,3‐diene is comparable to that of the benzene nucleus.
NMR of terminal oxygen. 1517O NMR spectra of the N+O− group: tert‐Amine oxides R3N+O−, nitrones HC  N+(O−), azoxy derivatives N  N+(O−), nitrile oxides  C  N+O− and related compounds. Shielding anisotropy in linear heteroatomar π‐systems
Authors: Dahn Hans , Péchy Péter , Van Toan Vien , Carrupt Pierre‐Alain
Published: May 2005

The 17O NMR signals of trimethylamine oxide and of six (para‐substituted) N‐aryldimethylamine oxides appear at 240–260 ppm, ca. 200 ppm more deshielded than hydroxylamines. The influence of the arene group and its substituents is small, confirming the absence of resonance interaction between the ring and the N+O− group. XN+(O−)Ar compounds (X =; R2C, nitrones; X = RN, azoxy compounds; X = ArN(O), azodioxy compounds = C‐nitroso dimers) are more deshielded, δo 350–450 ppm, due to resonance participation of NOtype structures (true nitroso compounds XNO appear at 650–1500 ppm). Carbonitrile oxides RCN+O− and NN+O− show high shielding, δo ca. 140 and 115 ppm respectively, higher than amine oxides; their C and N atoms also are significantly shielded. The increase in shielding, relative to sp2‐type π‐systems, is explained by the shielding anisotropy in linear (sp‐type) π‐systems. The shift values observed for four classes of NO compounds are in excellent agreement with predictions by IGLO calculations.
ESR study of the tricyclohexylmethyl radical
Authors: Luff Stefan , Morton John R. , Negri Fabrizia , Sharifi Mamood , Sutcliffe Leslie H.
Published: May 2005

The ESR spectrum of the tricyclohexylmethyl radical was obtained from tricyclohexylmethyl chloride and was studied in solution in the range 275–455 K. It has a half‐life of about 30 min at room temperature. The complex hyperfine structure of the radical was analysed with the help of MNDO/UHF calculations. Hyperfine interactions with three beta protons, twelve gamma protons and six delta protons were resolved. The alpha and the three beta carbon atoms are coplanar. The temperature dependence of the beta and six of the gamma proton hyperfine interactions was ascribed to torsional motions of the cyclohexyl rings about the CαCβ bond. The radical has C3h symmetry, the Cα and Cβ atoms being coplanar. Evidence for the existence of hexacyclohexylethane at about 200 K was obtained for the first time.
Preparation and steric structure of partially saturated isoindolo[1,3]‐ and ‐[3,1]benzoxazinones and ‐[2,4]benzoxazepinones
Authors: Sohár Pál , Stájer Géza , Nagy Katalin , Bernáth Gábor
Published: May 2005

From cis‐2‐(p‐methylbenzoyl)cyclohexanecarboxylic acid (1), diendo‐3‐(p‐methylbenzoyl)bicyclo[2.2.1]heptane‐2‐carboxylic acid (2) or 2‐(p‐methylbenzoyl)benzoic acid (3) with stereoisomeric 1,3‐ or 1,4‐amino alcohols with cyclohexane/ene or norbornane/ene skeletons, various partially or fully saturated isoindolo[1,2‐b] [1,3]‐ and ‐[2,1‐a] [3,1]benzoxazinones methylene‐bridged derivatives and [1,2‐c] [2,4]benzoxazepinones were prepared. For these compounds, containing two hetero rings and two or three cycloalkane rings, the stereostructures (the annelation of the terminal rings and aryl group) were established by 1H and 13C NMR spectroscopy, including DNOE, DEPT and 2D‐HSC measurements.
Structural investigation and conformational analysis of helianthosid 2, a saponin from Helianthus annuus L
Authors: Hiegemann Monika , Duddeck Helmut , Bader Gerd , Hiller Karl
Published: May 2005

The structure of helianthosid 2 was re‐examined by a spectroscopic investigation using one‐ and two‐dimensional NMR spectroscopy and all 1H and 13C signals of the saccharide part were assigned. NOE difference and ROESY experiments allowed a conformational analysis of the orientation of the monosaccharide units with respect to each other.
Complete 1H and 13C resonance assignment of 27‐norurs‐13‐en‐3β‐acetyloxy‐28‐oic acid by NMR spectroscopy
Authors: Jimeno M. L. , Rumbero A. , Vázquez P.
Published: May 2005

The first NMR study of a 27‐nortriterpene of the α‐amyrin type is described. In addition to conventional 1D NMR methods, 2D shift‐correlated NMR techniques (DQF COSY, TOCSY, HMQC and HMBC) were used for the complete 1H and 13C NMR resonance assignments of 27‐norurs‐13‐en‐3‐acetyloxy‐28‐oic acid.
Conformation of peptide T in aqueous solution. Determination of homonuclear coupling constants by selective HOHAHA techniques
Authors: Zangger Klaus , Sterk Heinz
Published: May 2005

The conformation of Peptide T in aqueous solution was investigated by means of 1H NMR spectroscopy in one and two dimensions. The data were compared with those obtained previously for the peptide in DMSO solution. While Peptide T forms a β‐turn in DMSO, no evidence was found for such a structure in water. Instead, Peptide T exists in aqueous medium in a random coil conformation with an increased tendency to form a stretched chain at the ends of the peptide backbone. This partly populated β‐strand was identified mostly by the analysis of atomic distances and coupling constants. To evaluate NMR parameters such as chemical shift and scalar coupling constants in the heavily overcrowded spectral regions, selective homonuclear Hartmann‐Hahn transfer was employed, which allows the observation of a distinct multiplet through the excitation of its scalar coupling partner, and subsequent magnetization transfer.
Ab initio study of the 13C nuclear shieldings for some polyenals and their schiff bases using LORG theory
Authors: Wada Mitsuhito , Sakurai Minoru , Inoue Yoshio , Tamura Yusuke , Watanabe Yoichi
Published: May 2005

Ab initio LORG (localized orbital/local origin) shielding calculations were applied to some polyenes and their Schiff bases. Computations were performed as a function of basis set quality. The use of polarization functions in the shielding calculations for these highly polarizable compounds gives good agreement with the experimental values even for the carbonyl and the imine carbons.
13C NMR of acyclic sulphonated compounds including some fluorosulphonic acids: A chemical shift study
Authors: Canselier J. P. , Boyer J. L. , Castro V. , Card G. L. , Mohtasham J. , Peyton D. H. , Behr F. E.
Published: May 2005

A chemical shift analysis of the 13C NMR spectra of more than 50 acyclic sulphonic acids, alkali metal sulphonates and methyl esters was carried out. Chemical shift increment systems with n‐alkanes as reference molecules were established for linear alkanesulphonates and alk‐2‐enesulphonates. Some short‐chain fluorinated sulphonic acids were also studied, especially pentafluorothio derivatives. CF spin‐spin coupling constants were determined. Pauling electronegativity values for SO3H and SF5 groups were derived from α chemical shift increments.
Characterization of new methyl‐substituted tetralins and indans by 13C NMR spectroscopy
Authors: Laurens T. , Schmit‐Quilès F. , Nicole D.
Published: May 2005

In order to perform the analysis of the components contained in fossil fuels, carbon assignments of new methylated derivatives of tetralin and indan were obtained. Their chemical shifts were calculated by applying additivity rules.
1H and 13C NMR assignment of theaflavin, theaflavin monogallate and theaflavin digallate
Authors: Davis Adrienne L. , Cai Ya , Davies Alan P.
Published: May 2005

Theaflavin, theaflavin monogallate and theaflavin digallate were isolated from black tea leaves and studied by 1D and 2D NMR techniques, thus allowing unambiguous assignment of the 1H and 13C resonances of these complexes. Earlier studies have not yielded 13C data of equal reliability, especially for the benzotropolone moiety of these molecules, and consequently the data given here will be of use in future studies of natural products isolated from tea. The utility of the 2D proton detected long‐range 13C1H correlation experiment (HMBC) in the study of polyphenolic complexes is demonstrated by these results.
Analysis of ABX spin systems in some 1,4‐dihydro‐1λ5, 4λ5‐diphosphinines: Signs of 31P13C coupling constants and isotope effects
Authors: Heckmann Gernot , Fluck Ekkehard
Published: May 2005

The ABX spin systems of the [mono‐13C]isotopomers with vinylic and phenyl ipso‐13C atoms of a number of symmetrical 1,4‐dihydro‐1,4‐diphenyl‐1λ5,4λ5‐diphosphinines were analysed. The substituent dependence of the absolute signs and magnitudes of 2J(PC) between the two 31P nuclei and two vinylic 13C atoms and of the 4J(PC) and 3J(PP) are reported. 13C isotope effects on δ(31P) and 3J(PP) are discussed.
Semi‐selective two‐dimensional homonuclear and heteronuclear NMR experiments recorded with pulsed field gradients
Authors: Dalvit Claudio
Published: May 2005

New two‐dimensional ω, and ω1, ω2 semi‐selective homonuclear and heteronuclear NMR experiments recorded with pulsed field gradients (PFGs) were designed and tested on two peptides. The use of PFGs improves dramatically the performance of the semi‐soft experiments. The complete absence of t1 modulations allows the observation of cross peaks which are buried in the noise. The same principle as described here can also be implemented for recording three‐dimensional and four‐dimensional semi‐soft experiments.
Structure elucidation of two diphenylhydantoin derivatives via 1H and 13C NMR spectroscopy
Authors: Ciechanowicz‐Rutkowska M. , Ragona L. , Greco F. , Zetta L. , Pegna M.
Published: May 2005

The solution conformations of 1‐benzyl‐5,5‐diphenyl‐2,4‐dioxo‐3‐imidazolidineacetic acid (AC) and 3‐(2,4‐dichlorobenzyl)‐5,5‐diphenyl‐2,4‐dioxo‐1‐imidazolidine acetic acid (AD) were studied by proton and carbon NMR spectroscopy. The two drugs have different pharmacological activities, AC having anticonvulsant and AD having antidepressant but no anticonvulsant properties. The relative orientations of the hydantoin ring substituents were investigated and are discussed in terms of amphipathic distribution of polar and apolar domains.
Hadamard long‐range proton‐carbon coupling constant measurements with band‐selective proton decoupling
Authors: Nishida T. , Widmalm G. , Sandor P.
Published: May 2005

Long‐range 13C1H coupling constants were measured by using multiple‐site selective excitation followed by polarization transfer and acquisition under band‐selective proton decoupling conditions. The multiple‐site proton decoupling eliminates splittings due to homonuclear spin couplings, thereby in practice simplifying the measurement of coupling constants from the anti‐phase splittings. In addition, the sensitivity is improved by approximately 50%.
79,81Br effects in the high‐resolution 13C NMR spectra of solid bromoaromatic compounds: Dipolar and indirect (79,81Br, 13C) interactions studied by ‘Inverse’ first‐order perturbation theory
Authors: Alarcón Sergio H. , Olivieri Alejandro C. , Carss Steven A. , Harris Robin K.
Published: May 2005

Splittings in the 13C cross‐polarization magic angle spinning spectra of 1, 4‐dibromobenzene and 4‐bromo‐3, 5‐dimethylpyrazole are reported. They arise from (79,81Br, 13C) interactions influenced by the quadrupolar nature of the bromine nuclei. They are analysed using both ‘inverse’ perturbation and exact theories to yield data on both isotropic and anisotropic coupling, including the signs. The spectra also enable the sign of the bromine quadrupole coupling constant to be confirmed as positive.
Isomeric equilibria of 1‐Methylamino‐2‐nitroethene
Authors: Kozerski L. , Krajewski P. , Bednarek E.
Published: May 2005

The solvent and concentration dependence of the isomeric equilibria of 1‐methylamino‐2‐niroethene were studied by 1H and 13C NMR spectroscopy. The results are used for clarification of the controversy regarding the content of the E form in CDCI3 solution, correcting an earlier suggestion concerning the stereochemical assignments around the C‐1N bond in the E form and verification of the values of the olefinic one bond proton—carbon spin—spin coupling constants, 1J(C,H), reported recently. An unambiguous means of assigning the stereochemistry around the C‐1N bond in the E isomer is suggested, based on using the complementary information from 3J(C‐2,NH) and 3J(H‐1,NH), in addition to the 3J(Me,H‐1) vicinal coupling constant.
1H and 13C NMR study of stereoisomers of 3‐(arylpropenylidene)isobenzofuran‐1(3H)‐ones
Authors: Sveshnikov Nikolay N. , Nikulin Victor I.
Published: May 2005

A study of the 1H and 13C NMR spectra of a series of E,E‐ and Z,E‐isomers of 3‐(arylpropenylidene)isobenzofuran‐1 (3H)‐ones [1a–d and 2a–d, respectively] was carried out. The E,E‐ and Z,E‐isomers 1a–d and 2a–d were recognized by the local anisotropy effect of the double and triple bonds of the substituents experienced by H‐4 in E,E‐isomers; in Z,E‐isomers; in contrast to their E,E‐analogues, upfield shifts of C‐4 and C‐8 due to the HH γ‐cis effect were observed.
The Townes and Dailey approach to the interpretation of NQR parameters in the light of non‐empirical calculations. Three‐membered rings
Authors: Balakina M. Yu. , Fominykh O. D. , Morozova I. D. , Osokin D. Ya.
Published: May 2005

The nuclear and electronic contributions to the EFG tensor components eqii at 14N, 17O, 33S and 35Cl nuclei in aziridine, methylaziridine, chloroaziridine, oxirane and thiirane were determined. The nuclear contributions were calculated within classical representations, while electronic contributions were calculated non‐empirically using a 6–31G* basis set within the framework of the LMO approach. On the basis of the analysis of the contributions to the EFG tensor components from definite bond and lone‐pair orbitals, the main concepts of the Townes and Dailey approach were tested.
1H and 13C NMR study of substituent effects in 2‐ and 3‐substituted diphenyl sulphides and sulphones and 4‐substituted 2′,6′‐dimethyldiphenyl sulphides
Authors: Perumal Subbu , Chandrasekaran Ramasubbu , Vijayabaskar Veerappan , Wilson David A.
Published: May 2005

The proton and carbon NMR spectra of nine 2‐substituted diphenyl sulphides (S‐2‐X), seven 3‐substituted diphenyl sulphides (S‐3‐X), nine 2‐substituted diphenyl sulphones (SO2‐2‐X), nine 3‐substituted diphenyl sulphones (SO2‐3‐X) and nine 4‐substituted‐2′,6′‐dimethyldiphenyl sulphides (Me2‐S‐4‐X) were obtained. Correlations of the 1H and 13C chemical shifts were made with benzene substituent‐induced chemical shifts (Lynch plots) and Hammett and dual‐substituent parameters and the results were compared with those of 4‐substituted diphenyl sulphides (S‐4‐X) and sulphones (SO2‐4‐X). The main conclusions are as follows: (i) the transmission of the substituent effects in substituted diphenyl sulphides decreases in the order S‐4‐X ≈︁ S‐2‐X > Me2‐S‐4‐X > S‐3‐X; (ii) the inductive effects are transmitted to a larger extent than the resonance effects to the unsubstituted ring in 3‐substituted diphenyl sulphides, while the reverse trend is observed in other substituted diphenyl sulphides; (iii) in 2‐methoxy‐, 2‐chloro‐, 2‐bromo‐ and 2‐nitrodiphenyl sulphides, an increase in the size of the substituent causes an upfield shift for H‐6 ascribable to the repulsion between the lone pairs of electrons on the sulphur and the substituent and its influence on the conformation; (iv) the diminished transmission of substituent effects to the remote rings in 4‐substituted 2′,6′‐dimethyldiphenyl sulphides is probably due to the orthogonal orientation of the rings; and (v) the signal due to the H‐6 of 2‐substituted diphenyl sulphones suffers a downfield shift with an increase in the size of the substituent, this being ascribable to the increasing steric interaction between the 2‐substituent and the sulphonyl oxygen and consequent changes in the conformation.
Solid‐state lead‐207 NMR of lead(II) nitrate: Localized heating effects at high magic angle spinning speeds
Authors: van Gorkom Leon C. M. , Hook James M. , Logan Michael B. , Hanna John V. , Wasylishen Roderick E.
Published: May 2005

Solid‐state Pb‐207 NMR spectra of lead(II) nitrate were found to be highly sensitive to variations in temperature. The Pb‐207 chemical shift exhibits a linear dependence on temperature with a positive slope of 0.70 ± 0.02 ppm K−1, i.e. increases in temperature cause a change in chemical shift to higher frequency. This slope is within experimental error of the value obtained from parallel experiments on the static solid, 0.72 ± 0.06 ppm K−1. At higher magic angle spinning (MAS) speeds and ambient probe temperature, the Pb‐207 signal splits into several components owing to localized heating effects. These effects are more pronounced in rotors made from partially stabilized zirconia than those made from silicon nitride and are attributed to the poorer thermoconductive properties of the zirconia ceramic. In the zirconia rotors, discrete thermal regions within the lead(II) nitrate sample were located and differ by 5 K at 12 kHz MAS speeds. The response of the Pb‐207 lead(II) nitrate signal to temperature variation suggests that it could be used for calibrating solid‐state NMR probes.
Determination of the molecular structure of s‐trioxane by NMR of partially oriented molecules
Authors: Esteban A. L. , Galache M. P.
Published: May 2005

The 1H and 13C NMR spectra of s‐trioxane partially oriented in three nematic solvents were analysed, and the measured dipolar coupling constants, corrected for harmonic vibrations and for correlated deformation, were used to obtain information about the rα structure of the molecule. It is concluded that the s‐trioxane molecule oscillates between two equivalent chair conformers and the methylene protons are tilted outwards from the threefold symmetry axis. The optimized values for the geometric parameters are 1.111 (2) Å for the CH bond length, 110.3 (3)° for the HCH bond angle and −2.1 (3)° for the methylene rocking coordinate.
NMR studies on the rhodium(I) chelates of two 2,3‐bis(O‐diphenylphosphino)‐β‐D‐glucopyranosides: Potent catalysts for enantioselective reactions
Authors: Michalik Manfred , Freier Thomas , Schwarze Manuela , Selke Rüdiger
Published: May 2005

The 1H, 13C and 31P NMR spectra of the 2,3‐bis(O‐diphenylphosphino)‐β‐D‐glucopyranoside rhodium(I) chelates 1 and 2 were recorded in CDCl3 solution and the spectral assignments were performed with 1D and 2D techniques. In both complexes the pyranoside ring has a chair conformation. For the seven‐membered chelate ring a twist‐boat conformation could be established for 1, whereas for 2 the expected twist‐chair conformation was found. The phenyl groups at the P atoms show unhindered rotation about the CphenylP bonds and the COD ligand seems to rotate about the RhCOD axis slowly on the NMR time‐scale.
Dynamic processes in solids: Three large‐amplitude processes revealed in a simple quaternary ammonium salt
Authors: Riddell Frank G. , Cameron Kenneth S. , Turnbull W. Bruce
Published: May 2005

13C CP/MAS NMR spectra of trimethyl(3‐phenylpropyl)ammonium bromide show evidence of three independent rotational processes in the solid: methyl rotation, trimethylammonium rotation and phenyl rotation.
Long‐range 37Cl/35Cl and 81Br/79Br isotope shifts in the 19F NMR spectra of some substituted fluorobenzenes
Authors: Bernard Guy M. , Schurko Robert W.
Published: May 2005

Long‐range isotope shifts, Δδ, due to 37Cl/35Cl and 81Br/79Br, in the 19F NMR spectra of some substituted benzenes are reported. The shifts appear to be invariant to solvent and are additive when the isotopes are in chemically equivalent positions relative to the fluorine site. The three‐bond isotope shift attributed to chlorine is approximately −1.60 ppb and that from bromine varies from −0.25 to −0.28 ppb. These shifts appear to be invariant to the substituent pattern. However, there is a large difference in the four‐bond shift for 2,6‐dichloro‐4‐fluorophenol (−0.16 ppb) and 2‐chloro‐6‐fluorocyanobenzene, (−0.55 ppb), suggesting that this isotope shift is mediated by the intervening group. In all cases, substitution by the heavier chlorine isotope resulted in increased shielding. The nearly equal natural abundance of 81Br and 79Br resulted in double peaks of approximately equal intensity. However, in almost all cases, the high‐field peak is of slightly lower intensity, suggesting that the sign of this isotope effect is also negative.
Conformational studies on B/C‐cis‐ and B/C‐trans‐morphinan derivatives
Authors: Szabó Zoltán , Marton János , Hosztafi Sándor
Published: May 2005

An unambiguous structural differentiation of B/C‐cis‐ and B/C‐trans‐morphinan derivatives (thebainone‐A and β‐thebainone‐A and their 7,8‐dihydro derivatives) is provided. The structures were confirmed by NOE difference spectroscopy and selective 2D J‐INEPT experiments. In addition, full a priori 1H and 13C NMR assignments of the isomeric pairs studied are presented.
Solution structures of the DP IV (CD26) inhibitor Val‐boroPro determined by NMR spectroscopy
Authors: Günther Ulrich L. , Sudmeier James L. , Coutts Simon J. , Snow Roger J. , Barton Randall W. , Bachovchin William W.
Published: May 2005

L‐Val‐L‐boroPro, a potent DP IV (CD26) inhibitor, and its non‐inhibitory diastereomer L‐Val‐D‐boroPro, were studied by 1D 1H and 11H NMR and by 2D 1H NMR methods in aqueous solution. Complete 1D 1H NMR fine structures were computer analyzed to obtain the 1H chemical shifts and spin‐coupling constants. Dihedral angles were derived from coupling constants on the basis of the Altona equation (i.e. an improved Karplus equation). The structures and populations of proline ring conformations were determined with the aid of pseudo‐rotation analysis. Good agreement between the distances derived from NOESY data and dihedral angle‐constrained force‐field calculations was obtained. Structural analysis allowed the identification of the absolute stereochemistry of the α‐carbon of the proline residue, and showed that the active inhibitor is the diastereomer which is homochiral with L‐proline. L‐Val‐L‐boroPro exists largely in a single conformer, in contrast to L‐Val‐D‐boroPro, which adopts two proline conformations in a 2:1 ratio. Analysis of 1H and 11H NMR spectra proves that inactivation of the inhibitor at physiological pH results from a cyclization reaction in which the free N‐terminal nitrogen atom forms a covalent bond with the B atom.