bluuebunny/crossref_metadata_2025_split huggingface dataset:
Further ESR studies of the cyclic sulphur nitride radical S3N2+ with a Q‐band spectrometer
Authors: Johnson K. M. , Preston K. F. , Sutcliffe L. H. 
Published: May 2005

AbstractFrom measurements made with both Q‐band and X‐band ESR spectrometers on powder samples enriched in 33S, it has proved possible to establish with improved precision the 33S hyperfine interaction tensors of the cyclic inorganic free radical 1,2,4,3,5,‐trithiadiazolyl,
equation image
. The best set of spectral parameters consistent with all of the data presently available is g = (2.0013, 2.0060, 2.0252), a(215N) = (36.4, <0.5, <0.5) MHz, a(233S) = (108.0, −15, −17.0) MHz and a(133S) = (−37.0, 10, 2) MHz, where tensor components are in the order x, y, z and x is the direction perpendicular to the molecular plane. The anisotropic parts of the hyperfine tensors lead to estimates for the unparied spin population in the atomic px orbitals perpendicular to the atomic plane of 42% (2S), 15% (2N) and (−) 16% (1S). A quadrupolar tensor e2Qq = (±32, ∓28, ∓4) MHz determined for the two equivalent 33S nuclei is consistent with the proposed electronic structure of the free radical.
77Se NMR studies of bis(alkylthio)selenides of biological thiols
Authors: Rabenstein Dallas L. , Tan Khoon‐Sin 
Published: May 2005

AbstractTo determine the feasibility of using 77Se NMR spectroscopy to characterize bis(alkylthio)selenides formed by reaction of selenite with thiol groups of biological molecules, 77Se NMR spectra have been measured for bis(alkylthio)selenides formed by reaction of selenite with cysteine, homocysteine, penicillamine, N‐acetylpenicillamine, 2‐mercaptopropanoic acid, mercaptosuccinic acid, cysteamine and glutathione. The 77Se chemical shift is extremely sensitive to the nature of the alkylthiol group, covering a range greater than 150 ppm for this series of thiols. The chemical shift is also sensitive to the stereochemistry of the alkylthiol group, and resolved resonances are observed for meso and D,L‐stereoisomers, e.g. the meso and D,L‐stereoisomers of bis(cysteine)selenide. 77Se NMR spectra were also measured for mixed bis(alkylthio)selenides (RSSeSŔ) formed by reaction of selenite with two‐component mixtures of the various thiols. The effect of the two alkylthiol groups on the 77Se chemical shift is additive, with 77Se chemical shifts of the mixed bis(alkylthio)selenides located mid‐way between those of the two symmetric compounds. The 77Se chemical shift is also sensitive to the protonation state of carboxylic acid and ammonium groups of the alkylthiol, and pKA values were determined from 77Se chemical shift vs pH titration curves for selected symmetrical and mixed bis(alkylthio)selenides. The results demonstrate that 77Se NMR is a sensitive method for the characterization and study of bis(alkylthio)selenides.
17O NMR study of chlorinated anisoles
Authors: Kolehmainen E. , Knuutinen J. 
Published: May 2005

AbstractThe 17O NMR chemical shifts of anisole and all 19 chlorinated anisoles measured in CDCI3 at ambient temperature show a dispersion of approximately 40 ppm. The substituent chemical shifts (SCS) of di‐ or more highly chlorinated compounds cannot be reproduced by addition of single substituent effects. Theoretical calculations of the 17O NMR chemical shifts have been attempted by molecular mechanical and semi‐empirical molecular orbital methods at the INDO level, but the results are not satisfactory.
Improved 13C1H shift correlation spectra for indirectly bonded carbons and hydrogens: The FLOCK sequence
Authors: Reynolds William F. , McLean Stewart , Perpick‐Dumont Marion , Enríquez Raül G. 
Published: May 2005

AbstractSeveral modifications of the basic 13C1H shift correlation sequence as optimized for polarization transfer via long‐range 13C1H coupling constants are described and evaluated. Modifications involve incorporation of BIRD pulse(s) at the mid‐point of the evolution period and/or at the mid‐point of the fixed delay prior to polarization transfer, in addition to the previously discussed incorporation of a BIRD pulse during the final fixed delay. These modifications give significantly improved sensitivity for many cross‐peaks, excellent suppression of one‐bond peaks and, in the case of the sequence incorporating two additional BIRD pulses, some ability to distinguish two‐bond and three‐bond connectivity peaks. The latter sequence is, overall, comparable in sensitivity to the fixed time sequences XCORFE and COLOC. It is also easier to parameterize and gives better suppression of one‐bond peaks and other artifacts.
NMR spectra and stereochemistry of 1,5‐ and 1,6‐disubstituted perhydrooxazolo[3,4‐a] pyridines
Authors: Crabb Trevor A. , Trethewey Andrew N. 
Published: May 2005

Abstract13C and 1H NMR spectroscopy showed that with the exception of r‐1,t‐6,t‐8a‐1‐alkyl‐6‐ethylperhydrooxazolo[3,4‐a] pyridines (alkyl = ethyl, isopropyl) which adopt the O‐inside cis‐fused conformation, all the other 1 ‐alkyl‐6‐ethyl‐ and 1‐alkyl‐cis(H‐5, H ‐ 8a) ‐5‐ methyl ‐ perhydrooxazolo [3,4‐a] pyridines adopt trans‐fused conformations (CDCI3, 298 K).
Complexes of aluminium with aminopolycarboxylic acids: 27Al NMR and potentiometric studies
Authors: Iyer R. K. , Karweer S. B. , Jain V. K. 
Published: May 2005

AbstractThe reactions of Al3+ ion with a series of aminopolycarboxylic acids containing coordinating sites (denticity, n) ranging from 3 to 8 were studied by potentiometric and 27AI NMR methods. Hydrolysis constants of the complexes were determined by potentiometry. The 27Al {1H} NMR data indicate a nearly linear relationship between the 27Al chemical shift of the normal complex and denticity of the ligand up to n = 6. Hydroxo complexes form in all systems, and at high pH (ca. 10) aluminate forms. Protonated complexes were formed in some cases. Diprotonated complexes of EDTA and PDTA have been identified by 27Al NMR spectroscopy. Maximum deshielding of the 27Al resonance was observed for the octahedral [Al(EDTA)]− complex. The Al‐NTA complex appears to be the most symmetric of the complexes.
13C NMR spectroscopy of aristolochic acids and aristololactams
Authors: Priestap Horacio A. 
Published: May 2005

AbstractThe 13C NMR spectra of more than 30 phenanthrene derivatives were recorded and their carbon shifts assigned. The compounds consisted of representative aristolochic acids and aristololactams, the phenanthrene alkaloid argen‐tinine and some derivatives. Assignments of the carbon resonances were carried out from chemical shifts, one‐bond and long‐range carbon‐hydrogen couplings and selective comparison of the phenanthrene derivatives with each other and with model compounds. The chemical shifts of the aromatic carbons were correlated with substituent effects. It was found that the shift changes on introduction of oxy functions in phenanthrenes parallel those reported for monosubstituted naphthalenes. Steric compression shifts observed in 3,4‐disubstituted and ring A polysubstituted phenanthrenes are discussed. Further evidence about the structures of the aristololactams CII, CIII, DII, DIII, enterocarpam‐I and enterocarpam‐II is provided, based on 13C NMR data. The substituent parameters found for phenanthrene derivatives proved to be additive and their use in signal assignments is described.
Molecular conformation trapping as an aid to chemical shift assignments for multi‐conformation systems: A platinum(II) complex
Authors: Luck Linda A. , Elesser Wendy L. , Hubbard John L. , Bushweller C. Hackett 
Published: May 2005

AbstractRecent work in our laboratory has shown that 31P{1H} dynamic NMR (DNMR) spectroscopy is useful in studying restricted rotation about the metal‐phosphorus bonds in bulky bis‐phosphine‐di‐halo complexes of platinum(II). Decoalescence is observed and the 31P{1H} NMR chemical shift is clearly sensitive to changes in molecular conformation. However, in most instances, the spectrum of a given conformation is a simple singlet which inherently contains no information regarding molecular geometry. Assignment of a given singlet to a specific conformation is problematic. A method is described for obtaining unequivocal assignment of NMR signals to specific molecular conformations by using DNMR spectroscopy. x‐ray crystallography and dissolution of the conformationally homogeneous crystals at very low temperatures (‘molecular conformation trapping’). This methodology should be useful for the analysis of any multi‐conformation system which has a sufficiently high energy barrier to conformational equilibration.
13C NMR of coumarins. II—Khellactones: Spectroscopic criteria to establish the relative configuration of the dihydropyran ring
Authors: Macías F. A. , Massanet G. M. , Rodríguez‐Luis F. , Salvá J. , Fronczek F. R. 
Published: May 2005

AbstractThe 13C NMR data of several khellactone derivatives are reported. 1H NMR‐based stereochemical criteria are evaluated, and a new criterion based on 13C NMR is proposed to establish the relative configuration at C‐3′ and C‐4′ using ΔδC‐3′ between trans and cis isomers and Δδgem(Me)2 values. The structure of trans‐4′‐methylkhellactone was determined by x‐ray analysis.
Two‐dimensional NMR studies of arsenical‐sulfhydryl adducts
Authors: O'Connor Richard J. , McGown Evelyn L. , Dill Kilian , Hallowell Susan F. 
Published: May 2005

AbstractBritish anti‐lewisite (2,3‐dimercaptopropanol) (BAL) has long been used as an arsenic antidote, but its therapeutic efficacy is limited by its inherent toxicity. Two less toxic potential replacements for BAL are dimercaptosuccinic acid and dimercaptopropanesulfonic acid. These two disulfhydryl compounds were compared with BAL by studying the structures of their adducts with two organic arsenicals, phenyldichloroarsine and trans‐2‐chlorovinylarsine oxide. The 1:1 adducts were synthesized and characterized by one‐ and two‐dimensional NMR spectroscopy. 1H and 13C spectral data and resonance assignments, verified by spin simulation, are presented for the adducts. All were five‐membered heteroatomic ring systems, with different solubility properties. When stereoisomers were detectable, the ratio of anti to syn isomers varied, indicating that the functional group of the antidote influenced stereochemical aspects of adduct formation.
2‐(4′‐Substituted) phenylisatogens: Analysis of 13C substituent chemical shifts
Authors: Stoddart B. , Hooper M. 
Published: May 2005

AbstractThe 13C NMR spectra for eight 2‐(4′‐substituted)phenylisatogens were determined at 30°C in CDCl3. Analysis of the ipso‐carbon SCS values was carried out using the well known DSP and DSP‐NLR models. Changes in the 13C SCS values for the carbon atoms in the isatogen moiety suggest that a small degree of inter‐ring mesomeric resonance is possible between the ring systems. A three‐parameter model, which give better overall agreement than either the DSP or DSP‐NLR models, is proposed for the ipso‐carbon SCS. The question of whether or not the isatogen moiety exhibits amphielectronic behaviour is still unresolved.
Carbon‐13 chemical shielding tensors in alkanedicarboxylic acids. Influence of molecular geometry on the carboxyl carbon tensors in alkanedicarboxylic acids and related compounds
Authors: Jagannathan N. R. 
Published: May 2005

AbstractThe principal elements of 13C chemical shift tensors in some dicarboxylic acids were determined from powder samples by two methods: (i) from the theoretical fit of the experimental data and (ii) from the side‐band intensities of the CP‐MAS spectra using the graphical procedure of Herzfeld and Berger. Neither the methylene nor the carboxyl carbons are axially symmetrical. The methylene tensors corresponding to higher dicarboxylic acids were not analysed owing to severe overlap of the different carbon tensors. The influence of local molecular geometry on the carbon 13C chemical shielding tensors in dicarboxylic acids and other related organic molecules are also reported. The σ22 component of the tensor shows a linear correlation as a function of the structural parameter, the OCO bond angle, around this carboxyl carbon atom. The significance of the symmetry factor calculated for the carboxyl carbons is also presented.
Probing the mechanism of ligand exchange by two‐dimensional NMR spectroscopy
Authors: Hampden‐Smith Mark J. , Ruegger Heinz 
Published: May 2005

AbstractThe application of two‐dimensional chemical exchange NMR spectroscopy to the elucidation of ligand‐exchange mechanisms in inorganic complexes is addressed. Specific examples involving inter‐ and intra‐molecular phosphine exchange in platinum and mercury complexes are given, and the generality of the technique is discussed.
Steric and electronic effects on 195Pt NMR chemical shifts of platinum (II) phosphine complexes
Authors: Clark Howard C. , de P. Nicholas A. Martin 
Published: May 2005

AbstractPlatinum‐195 chemical shift measurements for cis‐PtCl2(PCy3)2 and trans‐PtXCl(PCy3)2 (X = H, Cl, SnCl2Ph and SnCl3) in methylene chloride solution are reported. A comparison of these shifts with those from analogous complexes containing less bulky phosphine ligands indicates significant steric effects on the 195Pt shift of the PCy3 complexes. For cis‐PtCl2(PCy3)2 a downfleld shift of over 200 ppm is obtained. For the cis‐PtCl2(PCy3)2 complexes the deshielding of 195Pt is found to increase in the order X = H < Cl < SnCl3, SnCl2Ph, which corresponds to the change in the bulk of X. The observed downfield shifts in the bulky 2Ph complexes are rationalized in terms of steric crowding, lengthening of the PPt bond and deshielding of the Pt nucleus.
Transfer of substituent influence into the remote aromatic ring in 4′‐R‐dibenzo‐crown ethers
Authors: Loktev V. F. , Mudrakovsky I. L. , Tashmukhamedova A. K. , Stempnevskaya I. A. , Morozova I. J. 
Published: May 2005

Abstract13C NMR studies of 4′‐R‐dibenzo‐18‐crown‐6 and 4′‐R‐dibenzo‐24‐crown‐8 showed that the substituent influence is transferred through the macrocycle to a remote aromatic ring. The transfer is due to steric effects and depends on crown ether complex formation.
13C and 17O NMR study of methoxy groups in chlorinated Di‐ and trimethoxybenzenes
Authors: Knuutinen J. , Kolehmainen E. 
Published: May 2005

Abstract13C and 17O NMR data [chemical shifts and 1J(CH) values] for the methoxy groups in isomeric 1,2‐, 1,3‐ and 1,4‐dimethoxybenzenes, 1,2,3‐trimethoxybenzenes and most of their chlorinated derivatives and some related brominated compounds were measured for CDCl3 solutions. The 17O NMR chemical shifts show up to 60 ppm dispersion. Comparison between the compounds with and without adjacent chlorine atoms (2,6‐di‐ and 2,4,6‐tri‐substitution) also showed a clear methoxy carbon chemical shift change. The number and position of the chlorine atoms in the aromatic ring give small but observable effects on the 17O NMR chemical shifts of the methoxy group if it is coplanar with the aromatic plane. Similarly, the degree and nature of the substitution have a minor effect (about 1 Hz) on the 1J(CH) direct coupling values.
13C NMR study of aromatic ring‐substituted (E)‐3‐phenylpropenals and (2E,4E)‐5‐phenylpenta‐2,4‐dienals
Authors: Laihia K. , Pitkänen M. , Nevalainen Tapio 
Published: May 2005

Abstract13C and 1H chemical shifts together with C,H and H,H coupling constants are presented for (E)‐3‐phenylpropenal, (2E,4E)‐5‐phenylpenta‐2,4‐dienal and their o‐OCH3‐ and o‐, m‐ and p‐NO2‐substituted derivatives. The SCSs calculated for the aldehyde chains show similar effects on the ring carbons, except in the para position where the shorter chain causes a 3.3 ppm deshielding and the longer chain a 1.0 ppm shielding effect. This shift difference is reflected in all the ring‐substituted derivatives of the two series of aldehydes, but not in the one‐bond C,H coupling constants.The effect of aromatic ring substitution on 2J(C,CHO) seems to be mainly inductive in origin. The importance of the structural unit in the study of C,H coupling constants was observed on comparing the 3J(C,H) values in C(sp2)CCH and CCC(2)H pentadienal fragments. In the first type the vicinal coupling varies from 6.5 to 8.8 Hz and in the second from 2.7 to 3.6 Hz. In the latter fragment an s‐cis conformation changes the mutual position of the coupled nuclei, whereas in the former it remains the same as in the s‐trans conformation.
Exceptionally large 13C–13C coupling constants of compounds containing a CF3 group
Authors: Gombler Willy 
Published: May 2005

AbstractCoupling constants, 1J(13C,13C), of compounds containing a CF3 group are reported. The values for the coupling of the CF3 carbon with the neighbouring carbon are exceptionally large. In a series of compounds in which the CF3 group is bonded to an sp3, sp2 or sp carbon the 1J(C,C) values show a good linear correlation with the product of the s characters of the two orbitals forming the CC bond. Furthermore, compounds containing a CCl3 group have been measured. A correlation of the 1J(CC) values with the sum of the group electronegativities in compounds of the CX3‐CY3 type is found. The results for compounds containing highly electronegative substituents suggest a contribution to the CC coupling from a relatively large variation of the valence‐shell s‐orbital density at the carbon nucleus, Sc2(0). Additional 13C and 19F NMR data of the compounds are presented.
Multinuclear magnetic resonance study of tautomerism in fluorinated β‐diketones
Authors: Salman S. R. , Farrant R. D. , Lindon J. C. 
Published: May 2005

AbstractMultinuclear NMR experiments on fluorinated β‐diketones have furnished information on the various tautomers present in solution and their proportions. 2‐Trifluoroacetyl‐1‐indalone in CDCI3 solution exists in the enol form, as a mixture of exocyclic and endocyclic cis‐enols with the exocyclic form favoured, but in DMF‐d7 solution the equilibrium shifts to 40% enol, 60% hydrate with the enol and hydrate being in slow exchange on the NMR time scale. 2‐Trifluoroacetyl‐1‐tetralone in CDCI3 solution exists only as the enol forms, approximately equally populated, but in DMF‐d7, unlike the indalone, no hydrate is formed although there is now 6% of the keto form present in slow exchange. The experimental results were compared with calculated data produced using molecular orbital simulations. These agree with the NMR results and predict that the tetralone enol tautomers are both significantly populated at room temperature but that the indalone exists primarily as the exocyclic enol. The oxygen‐oxygen internuclear distance in the hydrogen bond was estimated from the OH proton chemical shift based on a calibration from solid‐state data from model compounds, and agrees well with the predictions using the molecular mechanics approach.
Conformation of zearalenone in solution: A vicinal coupling constant and molecular mechanics study
Authors: Muñoz Luis , Riguera Ricardo 
Published: May 2005

AbstractVicinal coupling constants of stereochemical significance were obtained in four solvents for zearalenone and specifically deuteriated zearalenone. Comparison with values calculated for several conformations using molecular mechanics calculations indicates that zearalenone exists in a single conformation in solution. The solvent dependence observed for the H‐9′ and H‐10′ signals cannot be attributed to a conformational equilibrium.
Carbon‐13 and related NMR chemical shifts in alkylammonium and alkylphosphonium salts
Authors: Evans David J. , Leigh G. Jeffery , Macdonald Colin J. 
Published: May 2005

AbstractThe 13C NMR chemical shifts of the α‐carbon atoms in cations [NR4]+, [NR3CH2Ph]+ and [PR4]+ [R = Me, Et, Prn, Bun or Pen (n‐pentyl)] are found at anomalously high field in comparison with the corresponding shifts in RCl or RNH2. This is ascribed in part to the effect of the positive charge. The effect is detectable but less pronounced with β‐carbon atoms, but is not detectable in subsequent carbon atoms in longer alkyl chains.
Applications of INEPT experiments for 119Sn NMR spectroscopy
Authors: Gouron Véronique , Jousseaume Bernard , Ratier Max , Lartigue Jean‐Claude , Petraud Michel 
Published: May 2005

AbstractThe application of a non‐refocusing INEPT pulse sequence in 119Sn NMR spectroscopy allows the determination of nJ(119Sn, 1H) values by comparison of the observed patterns with calculated spectra. It gives an easy access to nJ(119Sn, 1H) values in butyltin derivatives.
ESR study of the reaction of trithiazyl trichloride with primary aromatic amines
Authors: Domschke G. , Mayer R. , Bleisch S. , Bartl A. , Staško A. 
Published: May 2005

AbstractBenzenamines (1) react with 1,3,5‐trichloro‐1λ4,3λ4,5λ4‐1,3,5,2,4,6‐trithiatriazine (2) to form the novel radicals 2‐(2λ4‐2,4,‐dithia‐1,3‐diaza‐2‐chloro‐1,3‐butadien‐1‐yl)‐2λ4‐2,1,3‐benzothiadiazol‐1‐yls (4) or 2‐(5‐chlora‐2λ4‐2,4‐dithia‐1,3‐diaza‐1,2‐pentadien‐1‐yl)‐2λ4‐2,1,3‐benzothiadiazol‐1‐yls (4′). ESR hyperfine splitting constants of 20 different radicals of type 4 are presented, and the mechanism of their formation and the suggested structure of 4 are discussed.
17O and 31P NMR of aroylphosphanes, aroylsilanes and aroylphosphonates: Absence of resonance in —COPR2 groups (NMR of terminal oxygen, part 5)
Authors: Dahn Hans , Péchy Peter , Van Toan Vien 
Published: May 2005

AbstractThe 17O NMR spectra for aryl‐substituted P,P‐diphenylbenzoylphosphanes (p‐YC6H4COPPh2, 1), trimethylbenzoylsilanes (p‐YC6H4COSiMe3, 2) and dialkyl benzoylphosphonates (p‐YC6H4COPO(OR)2, 3) were recorded. Compounds 1, 2 and 3 show a similar high substituent sensitivity (p+), indicating a strong electron demand of the carbonyl group; as resonance stabilization is not possible in 2 and 3 it is concluded that electron donation from P to carbonyl is equally negligible in 1. The carbonyl oxygen signals of 1, 3 and, in particular, 2 appear at low field. The 31P NMR shifts of 1 were also measured; they are less sensitive to the ring substituents.
Compounds with bridgehead nitrogen. Part 64—conformational equilibria in the 6‐p‐nitrophenylperhydrodipyrido[1,2‐c: 2′,1′‐e]imidazoles
Authors: Banting Lee , Crabb Trevor A. 
Published: May 2005

AbstractThe effect of 6‐substitution on the conformational equilibria of the perhydrodipyrido[1,2‐c:2′,1′‐e]imidazoles has been investigated. r‐6H,t‐11a,t‐11b‐6‐p‐Nitrophenylperhydrodipyrido[1,2‐c:2′,1′‐e]imidazole was found to exist as a pair of enantiomeric non‐interconverting N‐outside‐cis‐syn‐trans conformers, whereas the r‐6H,c‐11a,c‐11b and r‐6H,c‐11a,t‐11b isomers adopted the trans‐syn‐trans conformations. Both syn isomers exhibit restricted rotation of the 6‐p‐nitrophenyl substituent at room temperature and below.
Compounds with bridgehead nitrogen. 65—NMR spectra and stereochemistry of perhydrodiquino[1,2‐c: 2′,1′‐e]imidazoles
Authors: Banting Lee , Crabb Trevor A. 
Published: May 2005

AbstractThe configurations and preferred conformations of six diastereoisomeric perhydrodiquino[1,2‐c:2′,1′‐e]imidazoles have been assigned by 1H and 13C NMR spectroscopy.