bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐field NMR studies of tert‐butyl cyanide in liquid and solid phases
Authors: Aksnes Dagfinn W. , Kimtys Liudvikas L. , Ramstad Kari
Published: May 2005

1H, 2H and 14N NMR line widths and spin—lattice relaxation times (T1) of tert‐butyl cyanide (TBCN) were measured at a field strength of 9.4 T in the liquid and solid states. The NMR line width data reveal the existence of two crystalline phases between 160 K and the melting point (292 K). The ordered phase (solid II) is observed throughout most of the temperature region on warming (170–290 K), indicating that the disordered phase (solid I), observed between ca 260 K and the melting point, is monotropic. The 1H line width of solid II is large and almost constant between 171 and 285 K (19–16 kHz), indicating slow whole‐molecule motion. The line narrowing of the 2H and 14N resonances observed above ca 260 K is ascribed to the onset of the whole‐molecule motion, slow overall molecular tumbling and fast C4 reorientations of the dipole axis. Activation parameters for the whole‐molecule motions and internal methyl and tert‐butyl reorientations (C3 and C3 motions, respectively) were obtained from the T1 data. The activation energy for the overall tumbling motion increases from 9.6 to 31 kJ mol−1 on freezing. This motion is very fast in the liquid (1.6 × 1012 s−1 at the melting point), but too slow to affect T1 in the solid phase. However, in solid I the molecular symmetry axis is also undergoing rapid, low‐amplitude reorientations with an activation energy of 8.9 kJ mol−1. The faster motion in solid II is the uniaxial C3′ reorientations with an activation energy of 15 kJ mol−1, while the slower motion is the C3 reorientation with an activation energy of 19 kJ mol−1.
Phosphorus 31P Spin–lattice relaxation times as a tool for the determination of the structure of 1,3‐dithianes with P‐containing substituents at the anomeric carbon atom
Authors: Mikolajczyk Marian , Wróblewski Krzysztof , Graczyk Piotr P.
Published: May 2005

Relaxation times, T, due to the dipolar mechanism of relaxation of 31P nuclei were determined for eight pairs of 1,3‐dithianes with P‐containing substituents at the anomeric carbon atom. The separation of dipole–dipole from the total spin–lattice relaxation could be applied for the unambiguous assignment of configuration of the compounds under investigation. The T relaxation times are smaller for compounds with phosphorus located axially (cis). This observation is discussed in terms of internal rotation around the C‐2 bond and the distances between the phosphorus and axial H‐4,6 protons.
Studies on ferrocene derivatives. VIII—1H nuclear magnetic resonance studies of 1,1′‐bis(o‐hydroxyphenyl)ferrocene
Authors: Okada Yutaka , Hayashi Takatoshi
Published: May 2005

In 1,1′‐bis(substituted‐phenyl)ferrocenes the protons of the second cyclopentadienyl (Cp) group are influenced by the ring current effect of the Ph group bonded to the first Cp group. The conformations of these derivatives are discussed with respect to the anisotropy of the Ph groups. The chemical shifts of 1,1′‐bis(o‐hydroxphenyl)ferrocene were unrepresentative in comparison with the other ortho derivatives. Both an OHO and an OH d type hydrogen bond are formed in this derivative, so that the two Ph groups are adjacent in the preferred conformation.
Two‐dimensional NMR analysis of selected photochromic spiroindolinonaphthoxazines
Authors: Malatesta V. , Allegrini P. , Neri C. , Lanzini L.
Published: May 2005

1H and 13C studies of a series of 19 photochromic spiroindolinonaphthoxazines were carried out by two‐dimensional NMR methods. The assignments of the 1H resonances were made by 2D homonuclear shift correlation (COSY) and the 2D nuclear Overhauser effect (NOESY). Complete 13C chemical shift assignments were carried out by using DEPT and two‐dimensional heteronuclear correlation spectroscopy.
Two‐dimensional NMR studies on the additivity rules for carbon‐13 chemical shifts in tetra‐n‐alkylammonium halides
Authors: Cheng Jinlong , Xenopoulos Alexander , Wunderlich Bernhard
Published: May 2005

The 13C chemical shifts of symmetric tetra‐n‐alkylammonium cations with n = 1–18 were identified unambiguously using two‐dimensional homonuclear (1H) chemical shift correlation (COSY) and heteronuclear (1H, 13C) chemical shift correlation spectroscopy (XHCORR). The 13C chemical shifts in small tetra‐n‐alkylammonium cations with less than five carbons in a chain are found to decrease from C‐1 (bonded to the nitrogen) (52‐60 ppm) to the methyl chain end (7‐14 ppm). For the cations with longer chains the values of chemical shifts are not in sequence with the carbon positions in an alkyl chain. The chemical shifts of C‐2 (22.5 ppm) are close to that of the methylene carbon next to the methyl group. The C‐3 carbon resonates at 26.4 ppm and is more shielded than the third carbon from the chain end (31.4 ppm). The chemical shifts of the remaining carbons are very similar to those of carbons in a corresponding linear alkane. The differences of the chemical shifts in alkylammonium salts from the corresponding n‐alkanes are largest for C‐1, C‐2 and C‐3, and this can be ascribed to the effects of the positive charge on C‐1, and the restricted segmental motion for the innermost region of the cations. Empirical additivity rules for the chemical shifts of C‐1, C‐2, and C‐3 are derived from the experimental results on 26 symmetric tetra‐n‐alkylammonium salts, and are tested for some asymmetrical systems with unequal chain lengths in the cation.
Quinazoline–iodine interaction as studied by NMR in nematic solutions
Authors: Suryaprakash N. , Khetrapal C. L. , Diehl P.
Published: May 2005

The results of an NMR study of the interaction of quinazoline with iodine in the nematic phase indicate the formation of at least two different types of charge‐transfer complexes. Significant changes in the molecular geometry of the quinazoline moiety were observed as a result of complexation with iodine. Detailed information on the formation of the charge‐transfer complexes was derived from the changes in the molecular structure, order parameters and chemical shifts as functions of iodine concentration. The observed changes in the order parameters are interpreted in terms of bond interaction tensors.
Conformation and dynamics in a solution of an N‐quaternized cinnamide derivative: A molecule active as a UV filter
Authors: Anselmi Cecilia , Centini Marisanna , Scotton Mirella , Sega Alessandro
Published: May 2005

The dynamics and conformation ofN,N‐dimethyl‐N‐[3‐(4‐methoxy‐trans‐cinnamoylamino)propyl]‐N‐n‐dodecylammonium bromide (1) have been established in two solvents (CDCl3 and DMSO‐d6) by the use of 13C spin–lattice relaxation rates, non‐selective and selective proton spin–lattice relaxation rates and 1H–(1H) NOE experiments. The two solvents affect the conformation of the cinnamide moiety in different ways. This alters the anchor capacity of the moiety towards the alkyl chain and, as a consequence, the dynamics of 1 in CDCl3 and DMSO‐d6 show understandable differences. However, the main mean conformations of 1 in both solvents are ‘linear’. The data do not allow the rationalization of the relationship between conformation and sunscreen efficiency.
η5‐Cyclopentadienyl derivatives of tin(II) studied by two‐dimensional multinuclear magnetic resonance in solution and by 13C and 119Sn CP/MAS NMR in the solid state
Authors: Wrackmeyer Bernd , Kupče Ēriks , Kehr Gerald , Sebald Angelika
Published: May 2005

Absolute coupling signs of 1J(119Sn, 13C) (<O) and 2J(119Sn, 1H) (<O) in (n5‐C5H5)2Sn (1) and 1J(119Sn, 13C) (<O)2J(119Sn, 13C) (O) in (n5‐C5Me5)2Sn (2) were determined using advanced direct and indirect two‐dimensional methods. These are based on Ψ‐BIRD techniques and z‐filtering, leading to pseudotriple‐resonance experiments of the type 1H{119Sn(13C)} and 13C{1H(119Sn)}, respectively. A mixed n5‐cyclopentadienyltin(II) amide was prepared and characterized by 1H, 13C, 29Si and 119Sn NMR in solution in the presence of its symmetrical redistribution products 1 and [(Me3Si)2N]2Sn. Solid‐state 119Sn CP/MAS NMR spectra of 1 shows the presence of two tin sites (in accord with the x‐ray analysis) with a 62.2 ppm difference in 119Sn chemical shifts, the mean value being in close agreement with the solution‐state δ119Sn value. The symmetries of the shielding tensor for the two tin sites are different and there appears to be a correlation between this property and the ring centroid—Sn—ring centroid angle α. 13C CP/MAS NMR proved insensitive to the structural differences between the two types of molecules of 1 in the unit cell.
Structure establishment by two‐dimensional NMR spectroscopy of the product obtained in the reaction of MCPBA and himachalol and revised 1H NMR assignments for himachalol
Authors: Agrawal Pawan K. , Frahm August W. , Schneider M.
Published: May 2005

The reaction of himachalol with m‐chloroperoxybenzoic acid afforded a rearrangement product, the structure of which was deduced by 2D NMR analysis to be 3α,4α‐epoxyhimachalane‐2α,7α‐diol. The recently proposed 1H NMR assignments for himachalol have been revised, based on the analysis of 2D COSY, DEPT, HETCOR and NOE experiments.
Solution behaviour and redistribution reactions of tetraorganodistannoxane dimers
Authors: Jain Vimal K. , Mokal V. B. , Sandor P.
Published: May 2005

The solution behaviour and redistribution reactions of tetraorganodistannoxane dimers were investigated by 19F and 119Sn NMR spectroscopy. The variable‐temperature NMR data suggest that both the ‘ladder’ and ‘staircase’ structures exist in solution. Redistribution between two different tetrabutylstannoxanes is rapid on the NMR time scale. The 119Sn 2D EXSY NMR data for [Bu2Sn(F)OSnBu2(Cl)]2 indicate that there is no exchange between exo‐ and endocyclic tin centres.
NMR studies of hindered rotation and thermal decomposition of novel 1‐aryl‐3,3‐dialkyltriazenes
Authors: Lippert Th. , Wokaun A. , Dauth J. , Nuyken O.
Published: May 2005

1‐Aryl‐3,3‐dialkyltriazenes have been synthesized by coupling the corresponding diazonium salts of substituted aniline derivatives with dialkylamines. The thermostability of these compounds was investigated by differential scanning calorimetry; activation energies of 240–280 kJ mol−1 were determined for the thermal decomposition. The hindered rotation of the dialkylamino group was studied by 1H NMR exchange measurements. Both experiments are interpreted in terms of an involvement of a 1,3‐dipolar structure of the NNN functional group. The influence of substituents, both on the aromatic ring and at the amino group, on the kinetic and activation parameters is investigated; results are analysed on the basis of mesomeric and steric effects on the dipolar charge distribution in the molecule.
1H and 13C NMR study of 2,3‐di‐ carboxymethyl‐7‐oxabicyclo[2.2.1]hepta‐2,5‐diene derivatives
Authors: Bighelli Ange , Tomi Félix , Casanova Joseph
Published: May 2005

13C and 1H NMR spectral assignments have been obtained for 2,3‐di‐carboxymethyl‐ 7 ‐oxabicyclo[2.2.1]hepta‐ 2,5‐diene and 19 of its derivatives. The use of a combination of one‐dimensional and two‐dimensional NMR techniques allowed the unambiguous assignments of all 13C resonances of the bicyclic framework.
Coherent and incoherent magnetization transfer in the rotating frame
Authors: Hwang Tsang‐Lin , Kadkhodaei Mehran , Mohebbi Afsaneh , Shaka A. J.
Published: May 2005

Two‐dimensional (2D) NMR spectroscopy has become a routine part of molecular structure determination in liquids. In most modern experiments there is some correlation of transition frequencies between the two dimensions, and the mechanism responsible for the correlation dictates the information obtainable from the 2D spectrum. Two distinct mechanisms for magnetization transfer are considered: scalar coupling and cross‐relaxation. The former gives rise to information about the proximity of spins through the electronic framework of the molecule and the latter provides information on spatial proximity and molecular motion. Two‐dimensional experiments of both types are described, concentrating in particular on TOCSY and ROESY. It is shown how polarization transfer can be tailored and controlled, and how the unwanted coherent transfer due to J coupling can be eliminated in the ROESY experiment. Throughout the discussion, the multiple‐pulse sequence used for each experiment is the central focal point, and its design and analysis are the main considerations.
Comparative evaluation of conventional 5 mm inverse and micro inverse detection probes at 500 MHz
Authors: Crouch Ronald C. , Martin Gary E.
Published: May 2005

Performance and sensitivity characteristics of a standard 5 mm inverse detection probe and a new micro inverse detection probe design were compared on identical amounts of material at 500 MHz. The latter consistently afforded approximately twice the signal‐to‐noise performance of the former in two‐dimensional experiments, corresponding to a factor of four improvement in performance times to obtain comparable signal‐to‐noise ratio projections of HMQC data. The latter also facilitated the acquisition of HMQC spectra on much smaller amounts of material than was possible in the conventional 5 mm inverse detection probe.
Structure elucidation by NMR spectroscopy of saccharolidin A, a novel antiparasitic macrolide from Saccharothrix aerocolonigenes
Authors: Swanson Alistair G. , Monday Robert A. , Perry David A.
Published: May 2005

The structure of saccharolidin A, C38H60O9, a macrolide with antiparasitic properties isolated from Saccharothrix aerocolonigenes, was determined by two‐dimensional NMR using a fragment‐directed approach. Complete elucidation of the structure required concerted application of a range of homo‐ and heteronuclear experiments (TOCSY, ROESY, HMQC, HMBC, HMQC‐TOCSY). Saccharolidin A is related to the hygrolides but contains a number of unique features which distinguish it from previously reported members of this family. It is unsubstituted on C‐2 and contains both a 1,3‐dioxepane ring and an unsubstituted n‐pentyl side‐chain. The relative stereochemistry within each of the three groups of contiguous chiral centres has been determined.
Long‐range deuterium isotope effects on 13C chemical shifts of intramolecularly hydrogen‐bonded compounds. Purpurogallins
Authors: Hansen Poul Erik
Published: May 2005

Long‐range deuterium isotope effects on 13C chemical shifts, nΔC(OD), were studied in the intramolecularly hydrogen‐bonded purpurogallins (benzotropolones). A very large long‐range isotope effect from the hydrogenbonded 4‐OH(D) is observed over six bonds at C‐7. Further, long‐range isotope effects are transmitted over as many as eight bonds. The transmission pathway including the carbonyl carbon is favoured, and some of the long‐range effects are transmitted via the carbonyl group. Large long‐range isotope effects are thus observed in hydrogen‐bonded systems with effective conjugation to the carbonyl group via alternating double bonds. This study indirectly supports recent theoretical predictions. The 13C and 1H NMR spectra of purpurogallin and its 2,3‐dimethyl, 2,3,6‐trimethyl and 2,3,4,6‐tetramethyl derivatives are assigned, and the hydrogen bond patterns are established based on the OH chemical shifts and 2ΔC(OD) isotope effects.
Determination and assignment of heteronuclear 119Sn1H coupling constants
Authors: Ratier Max , Jousseaume Bernard , Noiret Nicolas , Petit Nathalie , Lartigue Jean‐Claude , Pétraud Michel
Published: May 2005

nJ(119Sn, 1H) coupling constants were determined by 2D 13C1H and 119Sn1H non‐refocused COLOC (TPPI) correlation methods. As the 2D 13C1H method only gives access to coupling constants directly measured from the spectra, the proposed non‐refocused COLOC technique is more general since it allows measurements in the case of satellites which are non‐observable in 13C NMR spectra. An optimization method for the τ value in COLOC experiments is also proposed.
13C and 17O NMR spectra of ketenes: A new and unusual type of heavy‐atom effect
Authors: Duddeck H. , Praas H.‐W.
Published: May 2005

The 13C and 17O chemical shifts of a number of ketenes are reported and discussed in terms of electronic and mesomeric substituent influences. New deshielding α‐ and shielding γ‐heavy‐atom effects are reported. The corresponding data for carboxylic acid bromides and chlorides are given.
Improved 2D inverse proton detected C,H correlation NMR techniques for the total assignment of carbon resonances of a highly delta opioid receptor agonist peptide
Authors: Kövér Katalin E. , Prakash Om , Hruby Victor J.
Published: May 2005

Assignment of the 13C resonances of the highly delta opioid receptor selective cyclic peptide magnified image enkephalin (DPDPE) was accomplished by using single‐quantum inverse proton detected 2D heteronuclear correlation spectroscopy. The pulse sequences described provided better sensitivity and resolution than the corresponding, commonly used, multiple‐quantum evolution experiments, since during the SQ‐evolution period there is no line broadening due to scalar and dipolar 1H‐1H interactions. The proton detected C,H correlation spectrum, in combination with the H‐TOCSY relay C,H correlation, gave the assignment of all protonated carbons. The C,H correlation optimized for long‐range coupling gave the assignments of all non‐protonated carbons, such as the carbonyl carbons of the peptide bonds. These spectra also allowed the sequential assignment of this molecule.
Carbon‐13 NMR spectra of tetracyclododecanes: Evidence for upfield δ and ε steric effects
Authors: Seidl Peter Rudolf , Leal Kátia Zaccur , Costa Valentim Emilio Uberti , Möllmann Maria Elisabeti Stapoelbroek
Published: May 2005

13C NMR spectra of 36 endo–endo, exo–endo and exo–exo tetracyclic fused norbornyl compounds are interpreted. Stereochemical influences on 1H and 13C chemical shifts are compared and discussed. Only upfield δ and ε effects are observed.
Multifrequency ESR and NMR analysis of the metal–ATP interaction
Authors: Marchettini Nadia , Pogni Rebecca , Basosi Riccardo , Tiezzi Enzo
Published: May 2005

Multifrequency ESR analysis allows a new interpretation of the correlation times involved in nuclear relaxation. In this study the metal‐ATP interaction, so important in ecosystem energy mechanisms, was interpreted in the light of new multifrequency ESR and NMR experimental data. ESR spectra of the Mn(II)‐ATP complex were recorded at 2–4 GHz (S‐band), 9 GHz (X‐band) and 35 GHz (Q‐band). A loop‐gap resonator was used to enhance the ηQ0 product at low frequencies. The ESR line shapes at different temperatures and frequencies led to the interpretation of the predominant relaxation mechanism involved. The NMR relaxation rates, also recorded at different temperatures and frequencies, are discussed in terms of a motional model taking into account a distribution of correlation times. Structural and dynamic features were analysed in order to determine the effective correlation time contributing to nuclear paramagnetic relaxation. A comprehensive analysis of the multifrequency ESR spectra is crucial for the correct interpretation of the NMR spectra and of the metal–ATP interaction.
Method for the quantification of silicon‐29 NMR spectra, developed for viscous silicate solutions
Authors: Bahlmann Elke K. F. , Harris Robin K. , Say Barry J.
Published: May 2005

A method is described for obtaining quantitative intensity data from solution‐state spectra by a combination of coaxial tubes and sample replacement to take account of spectrometer electronic effects. The protocol was applied to two sodium silicate solutions of high silica content, and it is shown that there is no ‘invisible’ silica at the concentrations studied.
Gradient selection in inverse heteronuclear correlation spectroscopy
Authors: Willker Wieland , Leibfritz Dieter , Kerssebaum Rainer , Bermel Wolfgang
Published: May 2005

After a brief theoretical description, new gradient‐selected, proton‐detected heteronuclear correlation sequences are introduced. The gs‐HMBC and gs‐Relayed‐HMQC are closely related to the original gs‐HMQC proposed by Hurd and John. A new approach to obtain pure absorption line shapes in gradient selected spectroscopy is used to measure phase‐sensitive gs‐HMQC spectra, to carry out multiplicity editing in HSQC spectra and to distinguish direct and long‐range correlations in HMQC/HSQC–TOCSY spectra.
17O NMR studies on oximes
Authors: Cerioni Giovanni , Plumitallo Antonio
Published: May 2005

17O NMR spectra of some oximes were measured at natural isotopic abudance in pyridine and acetonitrile solutions; a clear δ effect was observed. No correlation with the SCS treatment was found for para substitution.
‘Through‐space’ hydrogen–fluorine, carbon‐fluorine and fluorine–fluorine spin–spin coupling in 2‐phenyl‐3‐alkyl‐4,5,6,7‐tetrahydroindazoles
Authors: Lyga John W. , Henrie Robert N. , Meier Gary A. , Creekmore R. William , Patera Russell M.
Published: May 2005

1H, 13C and 19F NMR experiments for a series of 3‐alkyl‐2‐phenyl‐4,5,6,7‐tetrahydroindazoles revealed a six‐bond through‐space coupling between the ortho‐fluorine and the hydrogen or fluorine atom of the position 3‐alkyl group. This was further supported by NOE experiments. Molecular mechanics calculations on a representative structure indicated that several low energy conformers met the fluorine‐carbon distance constraint suggested by the NMR data, and dynamic annealing experiments produced a conformer which was in complete agreement with the NMR data. This through‐space interaction is speculated to be a result of repulsion between N‐1 of the tetrahydroindazole and the ortho‐fluorine lone pair electrons.
Carbon‐13 NMR investigation of some substituted 1,3‐thiazolidin‐4‐ones
Authors: Woolston Christopher Richard Joseph , Lee John Barry , Swinbourne Frederick John
Published: May 2005

The 13C NMR spectra of a series of 2,3‐diaryl‐1,3‐thiazolidin‐4‐ones were measured and the resonance signals produced by the methylene, methine and carbonyl groups of the heterocyclic ring assigned. The variations in their chemical shifts were examined and the influence of S‐oxidation was investigated. 3‐Benzyl‐2‐phenyl‐1,3‐thiazolidin‐4‐one, 3‐butyl‐2‐phenyl‐1,3‐thiazolidin‐4‐one and 2,3‐diphenyl‐5‐methyl‐1,3‐thiazolidin‐4‐one were also examined, the last compound being shown to exist as a mixture of isomers. T1 relaxation times were determined for three thiazolidinones and related to structural effects.
E–Z isomerism of anilinomethylenemalonic acid derivatives
Authors: Bünz C. , Heber D. , Holzgrabe U. , Sürig U.
Published: May 2005

The temperature and concentration dependence of the 1H NMR spectra of four anilinomethylenemalonic acid derivatives were determined in CDCl3 and DMSO‐d6 to assign the E–Z isomers and to investigate the formation of intra‐ and intermolecular hydrogen bonds. Chemical shifts and coupling constants in the 13C NMR spectra correspond with the results of the 1H NMR investigations in the case of the cyanoacetate ester derivative. Contradictory results for the acetoacetate derivative were found by semi‐empirical calculations.
Eburnane‐14‐spiro heterocycles. Synthesis and stereostructure determination by NMR spectroscopy
Authors: Nemes András , Sohár Pál , Kövesdi István , Czibula László , Csehi Attila , Kreidl János
Published: May 2005

New spiroheterocyclic systems, eburnane‐14‐spiro‐5′‐oxazolidinedione, eburnane‐14‐spiro‐4′‐imidazolidinedione and related compounds were prepared by reacting vincamine stereoisomers or 14‐desoxy‐14‐aminovincamines with alkyl isocyanates. Stereostructures of the new compounds were proved by 1H and 13C NMR spectroscopy, including DR, DNOE, DEPT and 2D HSC measurements.
Structure determination of a new saponin from the plant Alphitonia zizyphoides by NMR spectroscopy
Authors: Perera Premila , Andersson Rolf , Bohlin Lars , Andersson Cristina , Li Du , Owen Noel L. , Dunkel Reinhard , Mayne Charles L. , Pugmire Ronald J. , Grant David M. , Cox Paul A.
Published: May 2005

High‐field NMR experiments, including the 2D INADEQUATE technique coupled with a computerized spectral analysis, were used to determine the full structure of a new saponin extracted from a plant (Alphitonia zizyphoides) found in the Samoan rain forests. The saponin, which shows significant pharmacological activity, consists of an aglycone framework of six rings (three saturated six‐membered rings, two oxygen‐containing five‐membered rings and a five‐membered carbon ring) to which are attached four sugar units and a six‐carbon side‐chain. The INADEQUATE experiment, which was carried out on 60 mg of sample, provided absolute confirmation of the assignments for 35 of the possible 53 CC bonds from the 13C–13C connectivities.
17O NMR spectroscopy: Study of intramolecular hydrogen bonding in phenols and salicylaldehydes
Authors: Boykin David W. , Chandrasekaran S. , Baumstark A. L.
Published: May 2005

Natural abundance 17O NMR data for fifteen 2‐ and 4‐substituted phenols, ten 3‐and 5‐substituted 2‐hydroxybenzaldehydes and eight 3‐substituted benzaldehydes, recorded at 75°C in acetonitrile are reported. The chemical shift change due to intramolecular hydrogen bonding for the phenolic oxygen was found to be 10–14 ppm shielding. In acetonitrile, the 17O NMR chemical shift for phenol signals was insensitive to added water up to water concentrations of 0.5 mole fraction. The 17O NMR chemical shifts of the 4‐substituted phenols gave an excellent correlation (r = 0.990) with anisole 17O NMR data; the data also correlated moderately well with σ− (r = 0.974). The chemical shifts of the 3‐substituted benzaldehydes were correlated with σ+ values (r = 0.991). A plot of the carbonyl chemical shift data for the substituted 2‐hydroxybenzaldehydes versus the carbonyl data for 3‐substituted benzaldehydes gave a slope of 0.87 and with r = 0.960. The plot of the 4‐substituted phenol data with that for OH of the corresponding 2‐hydroxybenzaldehydes gave a slope of 1.04 with r = 0.996. Proton to oxygen coupling for the phenolic group of several of the intramolecular hydrogen bonded systems was observed directly [J(OH) = 58–92 Hz]. MM2 and MOPAC calculations predict that the hydrogen bond distances and angles for the substituted 2‐hydroxybenzaldehydes and the partial atomic charges for the carbonyl groups (AMI) were essentially constant. After corrections for electronic effects the chemical shift changes due to hydrogen bonding for the donor (ΔδHBD) and acceptor (ΔδHBA) of the carbonyl–phenol intramolecular bonding system were 5–12 and 30 ± 2 ppm, respectively. The ΔδHBA value was between those for keto and ester acceptors consistent with the relative basicity of the aldehyde group. The ΔδHBD value was substantially larger than those for phenolic donors to keto and ester groups.
1H and 13C NMR assignments with coordination‐induced shift calculations of carbon σ‐bonded ortho‐metalated rhodium(III) and iridium(III) complexes
Authors: Garces Fred O. , Watts Richard J.
Published: May 2005

Complete 1H and 13C NMR assignments and coordination‐induced shift [CIS, δ(complex) – δ(free ligand)] calculations for carbon σ‐bonded ortho‐metalated rhodium(III) and iridium(III) complexes are described. NMR parameters are used as probes of van der Waals interactions and ring current anisotropy in the ligand's environmental framework and to monitor σ‐donation and π‐back‐bonding within the ligand in this family of ortho‐metalated complexes. CIS measurements indicate large charge redistribution within the ligands as a result of ortho‐metalation to the rhodium(III) or iridium(III) cationic metal centers. The pulse sequences, attached proton test (APT), 1H1H homonuclear correlation spectroscopy (COSY), single‐frequency off‐resonance decoupling (SFORD) and 1H13C heteronuclear correlation spectroscopy (HETCOR), were utilized to assign all proton and carbon resonances of [Rh(ppy)2Cl]2, [Ir(ppy)2Cl]2, [Ir(ptpy)2Cl]2, [Ir(mppy)2Cl]2, [Rh(ppy)2bpy]+, [Ir(ppy)2bpy]+, [Ir(ptpy)2bpy]+ and [Ir(mppy)2bpy]+, where ppy is 2‐phenylpyridine, ptpy is 2‐(p‐tolyl)pyridine, mppy is 3‐methyl‐2‐phenylpyridine and bpy is 2,2′‐bipyridine.
Conformation of ethane‐1,2‐diol from analysis of its NMR spectrum obtained using gradient‐enhanced inverse detection
Authors: Salman S. R. , Farrant R. D. , Sanderson P. N. , Lindon J. C.
Published: May 2005

The 1H NMR spectrum of [13C]ethane‐1,2‐diol was measured at natural abundance using the 1H13C inverse‐detected HMQC method with magnetic field gradients. A limited solvent and temperature dependence study was undertaken and the vicinal 1H1H coupling constants were related to those in model compounds. It is shown that the trans rotamer is significantly populated, in contradiction to some recent theoretical and experimental studies.
Substituent effects on ESR parameters of α‐phenyl‐N‐tert‐butylnitrone spin adducts. Resolution enhancement and mass spectrometry
Authors: Pan Kai , Lin Chiou‐Rong , Ho Tong‐Ing
Published: May 2005

The combination of high‐performance liquid chromatography (HPLC) and ESR spectrometry was used to isolate the free radicals produced by the reaction of a Grignard reagent with 15 substituted α‐Phenyl‐N‐tert‐butylnitrone. Long‐range hyperfine splitting constants (hfsc) were obtained by the resolution enhancement method. Linear correlation studies between hfsc and Hammett σp constants are reported. Dual‐parameter correlations using σR and σI were also studied. The mass spectra for the HPLC‐isolated spin adducts and their fragmentation patterns are reported.
1H and 13C NMR studies of proton transfer in intramolecular hydrogen bonds in substituted 2‐diethylaminomethylphenol N‐oxides
Authors: Brzezinski Bogumił , Brycki Bogumił , Maciejewska‐Urjasz Hanna , Zundel Georg
Published: May 2005

Eleven substituted 2‐diethylaminomethylphenol N‐oxides were studied in CDCl3 solutions by 1H and 13C NMR spectroscopy. The 1H chemical shifts of the intramolecular hydrogen‐bonded proton and the Δ14 values obtained from the 13C signals were considered as a function of the pKa values of the parent phenols. The 1H chemical shift of the hydrogen‐bonded proton shows a maximum at pKa ≈ 7. This result agrees well with the turning point of the curve if Δ14 is plotted as a function of the pKa of the parent phenols. All these results agree well with recently obtained Fourier transform IR results. With the system with the strongest hydrogen bond (pKa ≈ 7) a broad, flat, single‐minimum proton potential or a double‐minimum proton potential with a small barrier is present. With this system the deshielding of the proton in the intramolecular hydrogen bond is strongest.
Solution structures of [IrH2(1,5‐cyclooctadiene) (bisphosphine)](CF3SO3) complexes. Homo‐ and heteronuclear long‐range couplings from hydride and phosphorus spins to cyclooctadiene protons
Authors: Hälg Werner J. , Öhrström Lars R. , Rüegger Heinz , Venanzi Luigi M.
Published: May 2005

The solution structures of the two all‐cis stereoisomers of [IrH2(COD)((−)‐chiraphos)](CF3SO3) and the four all‐cis stereoisomers of [IrH2(COD)((−)‐norphos)](CF3SO3) [COD = cycloocta‐1,5‐diene, (−)‐chiraphos = 2S,3S‐bis(diphenyl‐ phosphino)butane, (−)‐norphos = 2R,3R‐bis(diphenylphosphino)norbornene] were assigned on the basis of various one‐ and two‐dimensional correlation methods. The rationalization of a specifically observed scalar coupling interaction between one of the hydrides and a methylene proton of the cyclooctadiene moiety required an assignment of all the relevant protons including their stereochemical relationship. Analogous long‐range coupling pathways were also found for the heteronuclear interactions nJ(P,H) and an interpretation of the origin of these scalar couplings is provided in the form of an expansion of the known geometric dependence of allylic and homoallylic couplings.
13C NMR spectra of trimethylsilylated secondary steroid alcohols
Authors: Schraml Jan , Čermák Jan , Kasal Alexander
Published: May 2005

The 13C NMR chemical shifts of 39 trimethylsilylated secondary steroid alcohols are presented. The compounds include both 5α‐ and 5β‐steroid skeletons and the trimethylsiloxy groups are attached at various positions both in α‐ and β‐configurations.
Analysis of long‐range through‐space couplings via an intramolecular hydrogen bond
Authors: Rae Ian D. , Weigold Josephine A. , Contreras Rubén H. , Biekofsky Rodolfo R.
Published: May 2005

2‐Fluorobenzamide and its N‐methyl derivative show spin‐spin couplings between the aromatic fluorine and the nitrogen and carbon of the amide group, which are absent in the corresponding N,N‐dimethylamide. The N‐methyl compound, in which there is a hydrogen bond between the fluorine and the amide hydrogen, also shows fluorine couplings to the nuclei of the methyl group, and these are diminished for solutions of the amide in polar solvents. Such couplings are absent in the N,N‐dimethylamide, which does, however, show fluorine couplings to the proximate methyl group. Calculations at the INDO level employing the IPPP method give reasonable agreement with the magnitudes of the observed 4J(F,N) values in the N‐methylamide and show that the Fermi contact contributions are dominant and that the spin information is transmitted mainly through the hydrogen bond.
Conformations and conformational interconversions of enantholactam
Authors: Borgen Gerd , Dale Johannes , Rise Frode
Published: May 2005

The conformational properties of enantholactam (1‐azacyclooctane‐2‐one) in solution were studied by 1H and 13C NMR at various temperatures. Only the cis‐isomer is present and it occurs in two different conformations in the ratio 3:2, as observed by 13C NMR at − 133°C. In the temperature range − 50 to − 140°C, two conformational processes were observed. A low energy process was visible in both the 1H and the 13C NMR spectra with coalescence temperature ca. − 110°C and a free energy of activation of 30 kJ mol−1, identified as interconversion between the two conformations. A higher energy process was visible in the 1H but not in the 13C NMR spectrum with coalescence temperature ca. − 96°C and free energy of activation 35 kJ mol−1. This process was identified as geminal 1H exchange. A conformational interconversion scheme for partial and full site exchange of protons and carbon atoms, explaining the variable‐temperature NMR results, is proposed.
High‐resolution solid‐state 13C CP/MAS NMR study of scleroglucan hydration
Authors: Bardet M. , Rousseau A. , Vincendon M.
Published: May 2005

Scleroglucan is a branched poiysaccharide, soluble in water. Solid‐state and solution 13C NMR were used to follow the fixation of water molecules on anhydrous scleroglucan and the evolution of the scleroglucan—water complex from the solid state to the gel and solution state. Determination of both chemical shift values and relaxation times (T, T1pH and T1C) for anhydrous and hydrated scleroglucans permit the observation of a transition between the two forms. The fixation of water leads to an increase in the solid‐state order, in the form of a triple‐helix association, and at the same time an increase in the interchain distance and in the molecular motion. The gel state obtained for a water‐scleroglucan composition of 90:10 is characterized by an important macromolecular rigidity which implies the use of the solid‐state NMR techniques. Solution 13C NMR can be utilized to characterize the primary structure and the triple‐helix random‐coil conformational transition.
Variable‐temperature NMR studies of 2,6‐dihydroxy acylaromatic compounds. Deuterium isotope effects on chemical shifts, isotopic perturbation of equilibrium and barriers to rotation
Authors: Hansen Poul Erik , Christoffersen Morten , Bolvig Simon
Published: May 2005

A series of 2,6‐dihydroxy acylaromatic compounds were investigated to characterize the rotational and hydrogen bonding properties of the carbonyl group. Deuterium isotope effects on 1H and 13C chemical shifts due to deuteriation of OH groups were determined at both ambient and low temperature. In the latter case isotope effects on chemical shifts of the individual rotamers can be determined. Deuteriation of one of the OH groups may lead to isotopic perturbation of the tautomeric equilibrium of the carbonyl group and the two hydroxyl groups. The perturbation was found to be larger in ketones than in esters. Complete band shape analysis of the OH resonances of the esters and ketones in a temperature interval above and below the coalescence temperature led to ΔG≠, AH≠ and ΔS≠ values for various concentrations of added THF‐d8. ΔS≠ was found to be strongly negative. Temperature coefficients for the shift of the OH resonances showed large variations for esters and ketones owing to the different hydrogen bond patterns. The esters have two intramolecular hydrogen bonds, one strong and an additional weaker one between the OH and OR groups. The second OH group of the ketones was shown to point primarily towards C‐5. Increasing amounts of THF‐d8 increased the amount of this rotamer. The anisotropy of the XCO group at C‐2, C‐6 was shown to lead to a low‐field shift of C‐2, very different from that found for CO groups without hydrogen bonds. The anisotropy caused by OH groups can also be estimated. On the basis of the thermodynamic parameters, a model for the rotation of the ester group is suggested. The rate‐determining step involves both intramolcular hydrogen bonds, which are twisted out of the ring plane to form hydrogen bonds to the solvent or other hydrogen bond acceptors.
Solvent versus substituent effects on the nitrogen NMR shielding of the nitro‐group in substituted benzenes
Authors: Witanowski Michal , Sicinska Wanda , Biedrzycka Zenobia , Webb Graham A.
Published: May 2005

Intermolecular effects are shown to induce a variation of about 5 ppm in the nitrogen NMR shieldings of aromatic nitro groups. The latter turn out to be comparable to those exerted by substituents in nitrobenzene derivatives in solutions in a given solvent. Substituent effects on the NO2 nitrogen shielding in nitro benzenes, in a given solvent, seem to reflect contributions from the so‐called field‐inductive effects on the electron charge distribution in such systems, and are insensitive to the resonance effects concerned with the delocalized pπ‐electron systems involved.
One‐dimensional multiple quantum filtration 1H NMR spectra of a 15‐mer DNA Duplex modified by the carcinogen 4‐aminobiphenyl
Authors: Cho Bongsup P. , Beland Frederick A. , Marques M. Matilde
Published: May 2005

The selective detection of the arylamine aromatic protons in a 15‐mer DNA duplex modified by the carcinogen 4‐aminobiphenyl was accomplished using one‐dimensional multiple quantum filtration experiments.
Electron spin resonance spectroscopy of free radicals
Authors: Fairhurst Shirley A. , Sutcliffe Leslie H. , Preston Keith F. , Banister Arthur J. , Partington Andrew S. , Rawson Jeremy M. , Passmore Jack , Schriver Melbourne J.
Published: May 2005

Solution and powder ESR spectra of the 4‐trifluoromethyl‐1,2,3,5‐dithiadiazolyl and 4‐pentafluorophenyl‐1,2,3,5‐dithiadiazolyl free radicals were analysed. Comparison of the ESR parameters with those obtained for the protonated equivalents shows that fluorination produces a drift of unpaired electron spin density away from the nitrogen 2px orbitals towards sulphur 3px orbitals (x is the direction perpendicular to the heterocyclic ring), consistent with an increase in electronegativity of the substituent. The fluorinated radicals dimerize more readily than their protonated counterparts.
Complete 1H (600 MHz) and 13C NMR spectral assignments of 3,4‐bis [(3,4‐dimethoxyphenyl)‐methyl]dihydro‐(3R‐trans)‐2(3H)‐furanone (matairesinol dimethyl ether), a naturally occurring dibenzylbutyrolactone lignan
Authors: Chimichi Stefano , Cosimelli Barbara , Bambagiotti‐Alberti Massimo , Coran Silvia A. , Vincieri Franco F.
Published: May 2005

The concerted applications of a variety of one‐ and two‐dimensional NMR techniques (COSY, NOESY, HETCOR, COLOC, etc.) to the structural elucidation of the natural 3,4‐bis[(3,4‐dimethoxyphenyl)methyl]dihydro‐(3R‐trans)‐2(3H)‐furanone, isolated from Oenanthe aquatica fruits, in CDCl3 solution are reported. The magnitude of the 1H,1H coupling constants obtained from the simulated spectrum together with a series of homonuclear NOE difference spectra were used to determine the full stereochemistry of the system.
Two‐dimensional 1H NMR studies on Desulfovibrio gigas ferredoxins. Assignment of the iron‐sulfur cluster cysteinyl ligand protons
Authors: Macedo Anjos L. , Palma P. Nuno , Moura Isabel , Legall Jean , Wray Victor , Moura José J. G.
Published: May 2005

1D and 2D 1H NMR studies are reported on the oxidized and reduced [4Fe‐4S] cluster of Desulfovibrio gigas ferredoxin I (Fdl). Several low‐field contact shifted resonances (fast relaxing) are assigned to β‐CH2 and α‐CH coordinated cysteinyl residues. NOESY patterns (supported by 1D NOE experiments) resolves four pairs of geminal β‐CH2 protons at low‐field. The cluster ligands are assigned non‐specifically to Cys8, Cys11, Cys14 and Cys50, based on the X‐ray structural analysis available for the oligomeric form, FdII, that contains a single [3Fe‐4S] cluster. It was indicated in this case that Cys11 is not bound to the trinuclear cluster but is tilted towards the solvent. The presence of four pairs of geminal β‐CH2 protons for FdI unambiguously proves the occupancy of the fourth site of the [3Fe‐4S] complex and implies the coordination of the Cys11 at the cluster. Analysis of the oxidized form of FdII, using the same methodology as described for FdI, supports the presence of three cysteinyl ligands in the [3Fe‐4S] core. Further, the combined use of the X‐ray coordinates enables the specific assignment of the three cysteinyl ligands of the cluster, extending a previous assignment of Cys50. In addition, very broad resonances were detected for the reduced form of FdII in the low‐field region around 200 ppm and in the high field region around −80 ppm.
Two‐dimensional 1H NMR studies of Ca(II)‐binding site in proteins using paramagnetic lanthanides(III) as probes and Yb(III)‐substituted bovine α‐lactalbumin as an example
Authors: Ming Li‐june
Published: May 2005

Substitution of Yb3+ for the Ca2+ in bovine α‐lactalbumin affords a derivative that gives rise to several isotropically shifted 1H NMR signals in the range 80 to − 35 ppm in D2O. Despite the broadness of the isotropically shifted features, cross signals in both NOESY and COSY spectra have been detected. Several Asp residues in the metal‐binding loop can be recognized in the 2D 1H NMR spectra of this derivative, showing cross signals among the protons of a CβH2CαH moiety. This paper reports 2D 1H NMR studies of a paramagnetic lanthanide(III)‐substituted Ca2+−containing protein that may serve as a model for future NMR studies of other biochemically significant Ca2+ proteins.
Spin—spin couplings between 13C nuclei in five‐membered heteroaromatic ring systems
Authors: Witanowski Michal , Biedrzycka Zenobia
Published: May 2005

A set of 14 1J(CC) spin—spin coupling constants are reported for 11 five‐membered heteroaromatic molecules, including all relevant diazole, triazole, oxazole, oxadiazole, thiazole and thiadiazole systems. The couplings show a clear distinction between carbon—carbon bonds which are formally double or single, respectively. There seems to be no correlation of the couplings with the bond lengths concerned, in spite of some apparent trends. Potential applications of the couplings are discussed in assessing the aromaticity of five‐membered heterocycles.
Long‐range carbon–proton couplings in strychnine
Authors: Blechta Vratislav , del Río‐Portilla Federico , Freeman Ray
Published: May 2005

Long‐range 13C,H NMR coupling constants were measured in strychnine at 400 MHz by a method that employs selective excitation of individual 13C sites under decoupled conditions followed by polarization transfer to protons. The sensitivity was improved by performing eight simultaneous soft‐pulse experiments coded (±) according to a Hadamard matrix and later separated by reference to the same matrix. The antiphase 13C,H splittings were measured by J‐doubling performed in the frequency domain.
Binding modes of the distamycin analogue FCE‐24517 to d(CGTATACG)2. 1H and 13C sequence‐specific assignments
Authors: Mazzini Stefania , Musco Giovanna , Ragg Enzio , Penco Sergio
Published: May 2005

The interaction of an analogue of distamycin, FCE‐24517, with the ‘AT‐rich’ DNA fragment d(CGTATACG)2, was studied in solution by the combined usage of 2D techniques, TOCSY, NOESY, ROESY and 13C/1H shift correlation experiments. The formation of the complex destroys the C2 symmetry of the double helix, leading to a doubling of the nucleotide resonances. Proton and carbon atoms were assigned in the complex in terms of specific strand and residue. The imino protons of the base pairs, involved in hydrogen bonding and the H‐2 protons of adenine moieties, were determinant for defining the binding sites of the drug. The presence of multiple equilibrium reactions was proved by means of NOESY and ROESY spectra, where all the chemical‐exchange cross peaks were analysed. The FCE‐24517 signals in the complex were attributed and some stereospecific assignments performed. Two sets of resonances for FCE were identified, showing that the drug exists in two different chemical environments, corresponding to two different modes of binding in slow chemical exchange. Significant intermolecular NOE interactions between the drug and the nucleotide have allowed the binding sites in the minor groove of the DNA fragment to be located.
1H, 13C, 17O NMR and IR spectroscopic study of all methyl chloropropanoates
Authors: Kolehmainen Erkki , Korhonen Ilpo O. O. , Kauppinen Reijo
Published: May 2005

1H, 13C and 17O NMR chemical shifts, nJ(H,H) and nJ(C,H) spin‐spin coupling constants and IR absorption maxima and intensities for the most characteristic bands of methyl propanoate and all eleven chloropropanoic acid methyl esters are reported.
Conformation of tricyclo [4.3.1.12,5]undec‐3‐en‐10‐one
Authors: Camps Pelayo , Vázquez Santiago , Jaime Carlos , Virgili Albert
Published: May 2005

A high preference for the boat conformation of tricyclo[4.3.1.12,5]undec‐3‐en‐10‐one was established on the basis of 1H NMR spectroscopy with the aid of molecular mechanics calculations (MM3 program).
Secondary isotope effect on the 19F shielding in xenon and krypton difluorides in solution
Authors: Jokisaari Jukka P. , Ingman L. Petri , Schrobilgen Gary J. , Sanders Jeremy C. P.
Published: May 2005

The effects of the various xenon and krypton isotopes on the nuclear shielding of 19F in xenon and krypton difluoride in solution were studied by 19F NMR spectroscopy. For both molecules, linear relationships were observed between the one‐bond secondary isotope shift of the 19F nucleus, 1Δ; 19F(m′/128Xe) and 1Δ 19F(m′/78Kr), and the relative mass factor, (m′ − m)/m′, and also between the shifts and the quadratic mean bond displacement, 〈(Δr)2〉. On the basis of the latter correlation and the linear relationship between 〈Δr〉 and 〈(Δr)2〉 for the linear combination of the first and second derivatives of the 19F shielding, the values −1742 and −5804 ppm Å−2, respectively, were determined. Further, the temperature dependence of the 129Xe and 19F chemical shifts and the 129Xe, 19F indirect spin‐spin coupling of XeF2 were determined. The 129Xe chemical shift is extremely sensitive to temperature with Δδ/ΔT = −0.4718 ppm K−1, whereas for 19F Δδ/ΔT = +0.0042 ppm K−1. In contrast, the 129Xe, 19F indirect spin–spin coupling is independent of temperature over the range 243–303 K, the mean value being 5644.2 ± 0.6 Hz.
77Se, 13C and 1H NMR spectra of phenylselenenyl azide and chloride addition products of methylenecyclohexane and cyclohexene
Authors: Boyko Walter J. , Duarte Franco J. , Giuliano Robert M.
Published: May 2005

The 77Se, 13C and 1H NMR spectra of the products of phenylselenenyl azide and chloride addition to methylenecyclohexane and cyclohexene are presented. Scalar couplings between 77Se and 1H/13C allowed the absolute assignment of the regioisomers in the 1H and 13C spectra. Low‐temperature 77Se NMR was used to determine the conformer ratios for 1‐azidomethyl‐ and 1‐chloromethyl‐1‐phenylselenenylcyclohexane anti‐Markovnikov addition products.