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Notes: The effect of lithium chloride on the relaxation mechanisms of simple acid and alcohols has been examined. Dipolar relaxation is predominant for acetic acid and ethanol. Lithium chloride (approximately 10%) significantly increases the rate of dipolar relaxation for all carbons and protons of acetic acid, probably through an increase in aggregate size or viscosity. Lithium chloride (approximately 1.5%) has a similar but smaller effect on the protons of ethanol. The methyl carbons and fluorines of trifluoroacetic acid and 2,2,2-trifluoroethanol relax primarily by spin-rotation. With about 10% lithium chloride, dipolar relaxation becomes more important for trifluoroacetic acid. With about 1.5% lithium chloride, trifluoroethanol possibly shows an enhancement of spin-rotation relaxation for the CF3 nuclei.
Newmark, Richard A. ; Siedle, Allen R.
Notes: Proton and 13C NMR spectra are reported for cis-(amine)Rh(CO)2Cl and trans-(amine)PtCl2(C2H4), where amine = tetramethylpyrazine, phenazine, phenazine N-oxide and quinoxaline. Relative labilities of the amine and ethylene ligands were determined.
Gate, E. N. ; Hooper, D. L. ; Stevens, M. F. G. ; [et al.] Threadgill, M. D. ; Vaughan, K.
Notes: A series of N-hydroxymethylamides, RCONR′CH2OH, and their O-methyl and O-acetyl derivatives, have been studied by 13C and 1H magnetic resonance spectroscopy. Signals have been assigned to the E- and Z-isomers on the basis of the analysis of the fully coupled spectra, and by comparison of the chemical shifts with those of model compounds. The introduction of the hydroxy, alkoxy or acetoxy groups at the α-position of the N-alkyl moiety causes a significant shift in the equilibrium towards the E-rotamer compared with the unsubstituted N-alkylamide. The predominant effect in determining the E: Z ratio appears to be the steric interaction between the carbonyl oxygen and the α-oxygen in the alkyl moiety; intramolecular hydrogen bonding does not play a significant role in determining the rotamer populations of these molecules.
Davies, David B. ; Rajani, Pramila ; MacCoss, Malcolm ; [et al.] Danyluk, Steven S.
Notes: A number of uracil cyclo-nucleosides with known glycosidic bond conformations have been synthesized as model compounds for evaluating the Karplus parameters of vicinal carbon-proton coupling across the glycosidic bond. The magnitudes of 3J(C-2, H-1′) and 3J(C-6, H-1′) were determined from proton-coupled 13C NMR measurements, and both coupling constants showed an approximate Karplus dependence with dihedral angle. Careful analysis of the results on model compounds reveals that the C-2, H-1′ and C-6, H-1′ coupling paths are not equivalent, and so the magnitudes of Karplus parameters have been determined for each coupling path for the Karplus relationship in the form 3J=A cos2 θ + B cos θ + C, i.e. A6 = 6.2, B6 = -2.4 and C6 = 0.1 Hz and A2 = 5.0, B2 = 2.1 and C2 = 0.1 Hz. Comparison is made between proton-carbon coupling magnitudes in nucleoside and peptide coupling paths.
Foster, N. ; Pestel, B.
Notes: The temperature-dependent 13C NMR spectra of a series of para-substituted 1-phenyl-3,3-tetramethylenetriazenes have been analyzed by the band width method. Electron-donating substituents clearly accelerate the rate of rotation about the N-2—N-3 bond in the triazenes; electron withdrawers retard that motion. The exchange averaging process observed in the carbon spectra obeys a linear free energy relationship when Hammett σ* parameters are used in the correlation. These results corroborate those already obtained by analysis of 1H NMR spectra of similar triazenes, regarding the likely contribution of a 1,3-dipolar resonance form to the ground state of the molecule.
Notes: CC coupling constants of ten bicyclic hydrocarbons and ten cyclic ethers or carbonyl compounds were determined from the satellites of broad band decoupled spectra or from INADEQUATE measurements. The influences of valence angles, dihedral angles, hybridization and heterosubstitution on geminal and vicinal CC coupling constants are discussed in terms of the algebraic additivity of the contributions from individual coupling paths within the framework of a multiple path mechanism.
Balicheva, T. G. ; Grechishkin, V. S. ; Petrova, G. A. ; [et al.] Shishkin, V. A.
Notes: 127I NQR frequencies have been measured in 20 compounds including iodates, chromate-iodates and tri-iodates. Quadrupole coupling constants and asymmetry parameters have been calculated at 77°K. Lines have been assigned by the two-frequency method. NQR data show the presence of covalent bonds in iodates and tri-iodates. In chromate-iodates the large value of the asymmetry parameter is due to the non-equivalence of an oxygen atom in the IO3- ion.
Abraham, R. J. ; Cooper, M. A. ; Whittaker, D.
Notes: The 220 MHz PMR spectrum of car-3-ene (3,7,7-trimethylbicyclo[4,1,0]hept-3-ene) is interpreted and a conformation deduced. In contrast to previous work, which has discussed a highly buckled structure for the 6 membered ring, the present work finds this ring to be essentially planar.
Description / Table of Contents: The PMR spectra of the title 1,3,2-oxazaphospholane derivatives present an ABKLX pattern. The subspectral analysis of such a system shows that there are eight solutions. INDOR experiments permit the establishment of the energy diagram and the selection of the correct solution.
Notes: Les dérivés de l'oxazaphospholane-1,3,3 du titre donnent des spectres de RMP du type ABKLX. L'analyse sous-spectrale d'un tel système montre qu'on a le choix entre huit solutions. Des expériences d'INDOR permettent d'établir le diagramme d'énergie et de choisir la bonne soultion.
Description / Table of Contents: In order to calculate empirically proton chemical shifts in methyl 1,3-dioxans, the basic values for each proton of 1,3-dioxan itself are estimated. Then, using methyl derivatives in the chair conformation, the Δδ primary effects of methyl groups in any position are given. Modifications take place in molecules with butane gauche interactions and these secondary effects are evaluated. Analogous Δδ in both the cyclohexane and dioxane series are related to similar cyclic geometry. The presence of oxygen atoms however, introduces important discrepancies.
Notes: Afin de calculer empiriquement les déplacements chimiques des protons de dioxannes-1,3 méthylés, nous avons tout d'abord dégagé les valeurs de base du déplacement chimique de chaque proton du dioxanne-1,3. ensuite, en utilisant des dérivés méthylés en conformation chaise, nous avons établi une systématique effets Δδ des groupes méthyles en position quelconque.Pour certaines molécules, présentant notamment des interaction gauches, ces divers effts peuvent être modifiés, et nous avons é ces perturbations. L'analogie de Δδ entre les deux séries dioxannique et cyclohexanique a été rapprochée d'une similitude de gémétrie des cycles. Cependant la présence des atomes d'oxygène introduit des différnces parfois importantes.
Maroni, P. ; Cazaux, L. ; Gorrichon, J. P. ; [et al.] Tisnes, P. ; Wolf, J. G.
Description / Table of Contents: The empirical calculation of chemical shifts of methyl-1,3-dioxans leads to consistent results. Deviations from the experimental value are correlated with ring deformation. This method is applied to 4 or 6-ethyl, -isopropyl and tertiary butyl-1,3-dioxans. With no substituent at C5, the 4-tertiary butyl group causes no more deformation than at the 2 or 5 position. Interactions of this group with one or two methyl groups at C5 are examined.
Notes: Le calcul empirique des déplacements chimiques de méthyl dioxannes-1,3 conduit à des résultats cohérents. L'écart avec la valeur expérimentale a pu être corrélé à la déformation du cycle dioxannique. La méthode a été étendue aux substituants éthyle, isopropyle et tertibutyle en position 4 ou 6 sur ce cycle.En l'bsence de substituant en 5, le groupe tertiobutyle n'induit pas plus de déformation du cycle en position 4 qu'en 2 ou 5. Les interactions particulières de ce groupement avec un ou deux méthyles en 5 sont mises en relief.
Notes: A PMR study of solvent effects on some p-substituted phenyltin chlorides (substituents = CH3, (CH3)3C, CH3O) is reported. Co-ordination of solvent molecules to the tin atom leads to an unusual low field shift of the o-ring protons. The results for p-tolytin trichloride have been compared with those for p-tolylsilyl trichloride and discussed. In o-, m- and p-tolyltin trichlorides long range spin-spin couplings between the ring methyl protons and the tin atom have been observed. The order of magnitude is o- > p- > m-methyl protons.
Notes: 13C NMR spectroscopy is an excellent tool for studying the influence of N-protecting groups on the cis/trans isomerism of proline residues in proline peptides. This communication demonstrates the usefulness of 13C NMR spectroscopy in investigating conformational problems in protein and peptide chemistry.
Kessenikh, A. V. ; Ignatenko, A. V. ; Rykov, S. V. ; [et al.] Shteinshneider, A. Ya.
Notes: A study of the CIDNP effects on methyl protons was carried out for the cage recombination products formed during the thermal decomposition reactions of peracetyls and peracetylcarbonates. The increase of both the cage recombination product yield and the enhancement of CIDNP on the CH3 protons is shown to be connected with the RCO2 radical lifetime, where R is an alkyl or alkoxy radical. A general theory of CIDNP is presented and the calculated data prove to be in satisfactory agreement with the experimental results.
Kessenikh, A. V. ; Ignatenko, A. V. ; Rykov, S. V.
Notes: The out-of-cage CIDNP effects, and kinetics of the out-of-cage reactions between the methyl radicals and the other radicals produced from the donor admixtures have been studied during the thermal decomposition of di-t-butylperoxalate (DTBPO). The DTBPO decomposition proves to be a good source of methyl radicals.The CIDNP effects on the methyl protons and on the nuclei of the other alkyl radicals are determined both by the out-of-cage radical collisions and the kinetics of out-of-cage recombination.
Vida, M. ; Cvengroš, J. ; Kello, V.
Sidorkin, V. F. ; Pestunovich, V. A. ; Voronkov, M. G.
Notes: The diamagnetic and paramagnetic terms of the 29Si nuclear shielding constant of silatranes, XSi(OCH2CH2)3N, and the related four-coordinated silicon compounds, triethoxysilanes, XSi(OC2H5)3, have been estimated to explain the experimental peculiarities of their 29Si NMR spectra. High-field shifts of the 29Si NMR signals of silatranes relative to triethoxysilanes are of diamagnetic origin, arising mainly from the existence of the Si←N bond and pentacoordination of the silicon atom in silatranes. At the same time, the decrease in the positive charge on the silicon atom upon Si←N interaction increases the absolute value of the negative paramagnetic term. When the Si←N bond in silatrane molecules becomes stronger through introduction of a more electronegative substituent X, the absolute value of the difference in the paramagnetic terms between silatranes and the related triethoxysilanes increases to a greater extent than that in the diamagnetic terms. This reduces the difference in 29Si chemical shifts of the corresponding four- and five-coordinated silicon compounds with increasing electronegativity of the substituent X.
Sohár, P. ; Pelczer, I. ; Váczi, I. ; [et al.] Tombor, A. ; Matolcsy, G.
Notes: N-Acyl derivatives of 1,3,3-trimethyl-6-azabicyclo[3.2.1]octane were synthesized as compounds with potential pesticidal activity. The conformation of the starting compound and the substituent dependence of the amide rotamers of the acyl derivatives were studied by 1 and 13C NMR spectroscopy, making use of solvent effects (ASIS) and DR, DNOE and DEPT measurements.
Kamounah, Fadhil S. ; Al-Sheibani, Ikbal. S. ; Shibaldain, Nazar L. ; [et al.] Salman, Salman R.
Notes: Proton NMR data for a number of 1-X-4-Y-3,5-dimethylbenzenes and 1-X-2-Y-4-Z-3,5-dimethylbenzenes are presented. The proton chemical shifts of the methyl groups at positions 3 and 5 are mainly affected by the ring current effect of the substituents. This conclusion was strongly supported by the proton chemical shifts calculated using additivity rules.
Spraul, M. ; Keul, H. ; Pfeffer, B. ; [et al.] Hähnle, J. ; Griesbaum, K.
Notes: The 13C NMR data of 42 ring-halogenated oxiranes containing fluorine, chlorine, bromine and, in one case, iodine as substituents are reported and discussed with respect to the influence of the halogen and of other substituents on the chemical shifts of the ring carbon atoms. For monocyclic mono- and dichlorooxiranes increments have been determined which allow the calculation of the chemical shifts of the ring carbon atoms. Comparison of the 13C NMR data of substituted 1,2-dihaloethylenes with those of the corresponding epoxides showed that the signals of the ring carbon atoms of the halogenated oxiranes always appeared at considerably higher field than those of the sp2 hybridized vinylic carbons in the respective precursors.
Notes: The conformations of the isopropyl groups and the barriers to conformational interconversion in N,N-diiso-propylbenzamide (1), and its thio (2) and seleno (3) analogues have been studied by dynamic 1H NMR spectroscopy. In 1 only one conformation is observed, whereas 2 and 3 exist as mixtures of three conformations. The use of the strongly deshielding C=X (X = O, S, Se) group and comparison with earlier results on similar systems allows total assignment, in the case of 2, rectifying an earlier proposal. The temperature dependence of the NMR spectra of 2 and 3 clearly shows that the E- and Z-isopropyl groups rotate with very different rates, thus providing experimental evidence for the stepwise nature of the conformational interchange.
Notes: The 13C NMR chemical shifts of 37 N-substituted 2,4,6-trimethylpyridinium (TMP) salts with alkyl, aralkyl, aryl and heteroaryl N-substituents are reported and discussed in comparison with those of the corresponding primary amines RNH2.
Notes: The 195Pt NMR parameters of several phosphorus-platinum(O) complexes [LnPt(O), L = phosphine or phospite, n = 2, 3, 4] have been investigated to illustrate the particular NMR properties of a spin-1/2 heavy metal nucleus, and for elucidation of their dependence on the geometry of the complexes. In these compounds the T1 values vary as a function of the coordination number, n, over several orders of magnitude and, therefore, can be used as structure-dependent parameters. In L2Pt complexes the relaxation rate varies with Bo2, and chemical shift anisotropy (CSA) is the dominant relaxation mechanism. In the L3Pt and L4Pt complexes spin-rotation increasingly contributes to the relaxation. For the tirethylphosphine-platinum complex (L3) the contribution of CSA is reduced by 45% at 7 T and 240 K, whereas the tetrahedral trimethylphosphine-platinum (L4) and triethyl phosphite-platinum (L4) complexes relax mainly by spin-rotation even at 9.4 T.
Christofides, John C. ; Davies, David B.
Notes: Application of the SIMPLE NMR method (secondary isotope multiplet NMR of partially labelled entities) to O-3′-sucrose derivatives in DMSO-d6 solution reveals the presence not only of the 1-OH Fru…-2-OH Glu intramolecular hydrogen bond in 3,3′,4′,6′-tetra-O-acety Isucrose, but also of an extensive hydrogen bond network in the glucose residue of 3′,6′-di-O-benzoylsucrose, i.e. 2-OH…3-OH…4-OH…6-OH.
Spassov, S. L. ; Markova, L. ; Mondeshka, D. M. ; [et al.] Tancheva, Ch. N. ; Angelov, Ch. M.
Notes: The vicinal 13C—31P couplings in the C—C=C—P fragment of alkenephosphonates (∼8 Hz for a cis- and ∼22 Hz for a trans-orientation of the respective nuclei) are a reliable and convenient parameter for the determination of the EZ configuration of these and analogous compounds.
Chazin, Walter J. ; Colebrook, Lawrence D.
Notes: Proton spin-lattice relaxation rates (R1 values) have been measured at 400 MHz for a series of substituted aromatic compounds to determine the steric effects of ortho substituents on the R1 values of the methyl groups. These values have been interpreted on the basis of differences in the barriers to methyl group rotation caused by the substituent, resulting in changes in the contributions from the dipolar and the spin-rotation relaxation mechanisms. A significant dynamic range of methyl R1 values has been observed, showing that these measurements are sensitive to the steric environment.
Häkkinen, A.-M. ; Ruostesuo, P. ; Kurkisuo, S.
Notes: The 17O, 15N and 13C NMR chemical shifts have been determined for N,N-dimethylmethanesulphinamide (1), both as the neat liquid and in dimethyl sulphoxide, acetone, chloroform and various alcohols. The 17O and 15N nuclei of 1 resonate at a lower frequency than those of the corresponding sulphonamide, and depend on the solvent and concentration of the components in binary solution mixtures. Hydrogen bond-forming solvents shift the signals to lower frequency than those of the neat amide. On changing the solvent, the change in the 17O NMR chemical shift of the sulphinamide is smaller than that of carboxamides, but the difference in the 15N NMR chemical shifts between these two systems with a solvent change is much lower and opposite in direction, reflecting the differences in the resonance structures of carboxamides and sulphinamides.
Lopyrev, V. A. ; Larina, L. I. ; Vakul'skaya, T. I. ; [et al.] Shibanova, E. F. ; Titova, I. A. ; Voronkov, M. G.
Notes: The substituent effects in dianion radicals of fourteen 2-substituted 5(6)-nitrobenzimidazoles, electrochemically generated in acetonitrile, were studied by ESR. It was found that the substituent influence on the nitro group is transmitted with approximately equal contributions from the inductive and resonance components, independently of the pairs of the σIσR, σIσRo,σIσR+ and FR substituent constants used. The radical stabilization constant σ contributes much to the correlation of the hyperfine splitting constants of H-6 and the heterocyclic nitrogen atoms. The transmission through the benzimidazole ring in dianion radicals of nitrobenzimidazoles is half that of the benzene ring in anion radicals of para-substituted nitrobenzenes.
Aversa, M. C. ; Giannetto, P. ; Saija, A.
Notes: By observing the shifts of the 1H NMR signals of 1,4-benzoquinones induced by Eu(fod)3, and simulating them with the aid of a novel computer program TWOCEN, it has been shown that the two carbonyl groups of 1,4-toluquinone and 2,6-dimethyl-1,4-benzoquinone compete in the Eu coordination. The metal binds at two sites on both the carbonyl groups, with 4-CO having a greater complexing ability with respect to 1-CO, in line with steric and electronic considerations.
Notes: A survey of recent high-resolution solid-state 13C NMR studies is given to illustrate how and to what extent 13C chemical shifts of a variety of molecular systems are displaced upon conformational changes. Examples are taken from studies of alkanes, polysaccharides, polypeptides, and naturally occurring and synthetic ionophores, in which more than single conformations are available owing to either crystalline polymorphs or a variety of metal-ligand interactions. The magnitude of the conformation-dependent 13C chemical shifts are in many instances as large as 8 ppm and are well related to a set of torsion angles of nearby single bonds. The application of this concept to conformational characterization is also discussed.
García-Granados, A. ; Martínez, A. ; Onorato, M. E. ; [et al.] Santoro, J.
Notes: A detailed analysis of the 13C NMR spectra of 39 isomeric ent-beyer-15-enes and ent-beyeranes functionalized at C-7, C-14, C-15 and C-16 has been performed. This diterpenic skeleton is a good example of a semirigid bicyclo[3.2.1]octane system. The sensitivity of 13C shielding to the stereochemical environment, particularly in polyfunctional compounds, has been confirmed. In some cases the ent-beyer-15-enes and ent-beyeranes show similar behaviour to that of similarly functionalized bicyclo[3.2.1]octane derivatives, but in other cases the shielding effects are very different. The compounds studied are a good model for the evaluation of shielding effects in exo/endo isomers of strained and rigid carbocyclic compounds.
Notes: Aromatic 13C chemical shifts are reported for an extensive set (15 common substituents) of 1,3-disubstituted benzenes measured at low concentration in deuteriochloroform. The substituent chemical shift data show systematic non-additivity. Data for the para- and two meta-positions to the variable substituent were analysed using the recently developed non-linear resonance (DSP-NLR) and standard (DSP) dual substituent parameter equations. It is shown for these positions that mutual substituent interaction is responsible for the non-additive shifts and that (a) this interaction has both an inductive (polar) and a resonance component, even for meta-oriented substituents, and (b) the shift-charge ratio term extends past the ipso-position. These results are discussed in terms of local paramagnetic shielding contributions to 13C shifts.
Knight, Christopher T. G. ; Harris, Robin K.
Notes: The 29Si spin-lattice relaxation times, T1(29Si), of the various silicate anions present in high-purity alkaline silicate solutions are reported. Regular silicate cages display the longest T1(29Si) values and, in the case of the cubic octameric cage, an unexpectedly large nuclear Overhauser enhancement, indicating that, unlike the smaller silicate oligomers, the cubic octamer relaxes primarily via the (29Si, 1H) dipole-dipole interaction. This phenomenon provides, inter alia, a simple diagnostic test for such cages.
Notes: The 13C NMR spectra of three naphtho-γ-pyrones produced by Aspergillus fonsecaeus (NRRL 67, 0 16-1), viz. 5-hydroxy-6,8-dimethoxy-2-methyl-4H-naphtho[2,3-b]pyran-4-one (rubrofusarin B), 2,3-dihydro-2,5-dihydroxy-6,8-dimethoxy-2-mehtyl-4H-naphtho[2,3-b]pyran-4-one (fonsecin B) and 2,3-dihydro-2,5,8-trihydroxy-6-methoxy-2methyl-4H-naptho[2,3-b]pyran-4-one (fonsecin), have been determined. Assignments of the carbon resonances were carried out from chemical shifts, long-range carbon-hydrogen couplings and hydrogen-deuterium exchange information. Carbon shift assignments previously reported for fonsecin have been revised. The C-4 and C-5 signals show that the angle of twist of the carbonyl group with the aryl ring system is larger in fonsecin than in fonsecin B, indicating the occurrence of different preferred conformations in the dihydropyrone ring of these compounds.
Notes: The assignment of some 1H and 13C NMR chemical shifts of apigenin have been uncertain and even contradictory. A reinvestigation with recent NMR techniques has led to a new set of 13C NMR parameters and confirmed the accepted 1H NMR data.
Faure, R. ; Vincent, E. J. ; Gaydou, E. M. ; [et al.] Rakotonirainy, O.
Notes: Total assignment of the 13C nuclear magnetic resonance spectrum of α-longipinene was achieved from DEPT and double quantum coherence measurements, while concerted application of 1H—1H homonuclear and 1H—13C heteronuclear two-dimensional chemical shift correlations provided all proton chemical shifts.
Jones, D. W. ; Pakdel, H. ; Hallas, G. ; [et al.] Hepworth, J. D.
Notes: Four new dimethylaminated pyridoylpyridine intermediates, bis(3-dimethylamino-2-pyridyl) ketone (1), 6-dimethylamino-3-pyridyl 4-pyridyl ketone (2), 6-dimethylamino-3-pyridyl 3-pyridyl ketone (3) and 6-dimethylamino-3-pyridyl 2-pyridyl ketone (4), have been synthesized and their 100 MHz 1H NMR spectra analysed iteratively as ABC, ABCX and ABXY spin systems. In 2-4 the H-5 shift ortho to the dimethylamino substituent is unaffected by the orientation of the pyridyl substituent, but H-4 and H-2 are increasingly deshielded in the sequence 2-4. In 3, when benzene-d6 replaces chloroform-d1 as solvent, H-5′ and H-4′ in the unsubstituted pyridyl ring suffer appreciable upfield shifts.
Szalontai, G. ; Bakos, J. ; Tóth, I. ; [et al.] Heil, B. ; Pelczer, I. ; Sohár, P.
Notes: 13C, 1H and 31P NMR investigations have been carried out to determine the ring stereochemistry and phosphorus configuration for four chiral (4R, 6R)-2-substituted-1,3,2-dioxaphosphorinane derivatives 1-4 (2-substituent = Cl, Ph, OMe and O-t-Bu, respectively). 1H NMR spectra, double resonance, 2D-J experiments and spin simulation proved the chair character of the ring. Depending on the position of R, two diastereomers may exist, but in most cases only one predominating form was detected. Dynamic processes were observed for 1 and 2. Saturation transfer experiments proved the existence of ring and/or phosphorus inversions.
Notes: A large number of intramolecularly hydrogen-bonded molecules were investigated by means of deuterium isotope effects on 13C nuclear shielding. The compounds illustrate three different types of molecules: compounds with a localized hydrogen bond (strongly asymmetric double minimum potential), and tautomeric molecules of symmetrical or unsymmetrical nature (symmetrical or almost symmetrical double minimum potential). In the localized case the strength of the hydrogen bond reflects itself in the magnitude of 2Δ COD. The presence of a hydrogen bond is, furthemore, demonstrated in an orientational dependence of 3Δ COD, and usually also in the presence of an 3Δ COD. The tautomeric systems can also be characterized by means of deuterium isotope effects. Investigations of β diketones showed the presence of an equilibrium isotope effect. Large long-range isotope effects of naphthazarin are explained in a similar manner. Tautomerism was established in usnic acid and the type of tautomerism was determined. 2,6-Dihydroacetophenone shows an interesting type of perturbation of the equilibrium on unsymmetric deuteriation.
Notes: The interaction of caffeine and theophylline with sodium benzoate and sodium salicylate has been studied in deuterium oxide at 35 °C by measuring the aromatic salt-induced changes in the chemical shifts of the N-methyl protons. Taking into account the self-association of the N-methylxanthines, on the basis of a 1:1 complexation model the association constants for caffeine-sodium benzoate, theophylline-sodium benzoate, caffeine-sodium salicylate and theophylline-sodium salicylate were found to be 2.1 ± 0.1, 1.5 ± 0.2, 7.8 ± 0.2 and 5.0 ± 0.21 mol-1, respectively.
Notes: The 13C NMR data for 3-aminoindazole and 14 aminopyrazoles were obtained in neutral and acidic media (trifluoroacetic acid) and compared with those for a series of pyrazoles, aminothiophenes and anilines as models for protonation. From the chemical shifts and coupling constants it is possible to conclude that all 3-aminopyrazoles, 3-aminoindazole and 5-aminopyrazoles protonate on the heterocyclic ring nitrogen atom. This first protonation strongly deactivates the exocyclic nitrogen atom, so that no double protonation is observed, even in sulphuric acid. On the other hand, 4-aminopyrazoles are stronger bases, which are protonated first at the amino group and then on both nitrogen atoms.
Notes: Some biologically relevant derivatives of catechol, phenol and benzene were studied by 13C NMR spectroscopy. The 13C chemical shifts of the aromatic ring are discussed in terms of the polarizing ability of the substituents.
Maat, L. ; Peters, J. A. ; Linders, J. T. M. ; [et al.] Hussein Ayoub, S. M.
Notes: Tetrahydro-2-(3,4 -dimethoxyphenyl)-4-[(3,4-dimethoxyphenyl)methyl]-3-furanmethanol has been isolated from Monechrna ciliaturn. Its structure was deduced from the 200 MHz 1H NMR spectrum.
Notes: A full analysis of the 1H NMR spectra of angelicin (2H-furo[2,3-h]-l-benzopyran-2-one) and of 25 of its mono-, di- and tri-methyl analogues, allows the assignments of all the peaks in the spectra to be made with reasonable certainty. Coupling constants have also been utilized in order to provide a better fit of the data.
Notes: The 15N chemical shifts and the one-, two- and three-bond 15N-1H spin-spin coupling constants for ten unenriched barbituric acid derivatives have been measured at 10.14 MHz in dimethyl sulphoxide-d6. The measured 15N chemical shifts are in three distinct ranges: -270 to -280 ppm for urea-type nitrogens, approximately -264 ppm for amide-type nitrogens and between -226 and -236 ppm for imide-type nitrogens, in accord with the gradually increasing possibility for delocalization of the nitrogen lone-pair electrons. The 2 ppm shielding effect of the side-chain hydroxy group, together with the 5 ppm shielding effect of the N-methylation on the ring nitrogens, allows the identification of the diastereoisomers of 5-allyl-5-(2-hydroxypropyl)-1-methyl-2,4,6(1H,3H,5H)-pyrimidinetrione. The three-bond coupling constant of 1.5 ± 0.2 Hz found in five compounds is a unique example of pure trans-type spin-spin coupling over an N—CO—N—H path. This study shows that particular attention must be paid to sample preparation and measuring conditions in order to achieve structurally significant nitrogen chemical shift and coupling information.
Häkkinen, A.-M ; Ruostesuo, P.
Notes: 15N, 17O and 33S NMR chemical shifts were determined for some aliphatic and aromatic sulphonamides, sulphinamides, sulphenamides and related sulphones and sulphoxides. The 17O and 33S NMR chemical shifts change only slightly for the sulphonyl compounds. In the sulphinyl compounds, on the other hand, the presence of nitrogen causes a noticeable shift to higher frequencies in the 17O resonance. The differences between the 17O chemical shifts of sulphinyl and sulphonyl compounds are more noticeable than those between sulphinamides and sulphoxides. The 15N NMR chemical shifts of sulphon-, sulphin- and sulphen-amides reflect well the effect of the environments of both nitrogen and the adjacent sulphur atom. The correlations between 15N, 17O and 33S NMR chemical shifts and the structures of sulphur amides and related sulphones and sulphoxides are discussed. The chemical shifts of the 13C nuclei are also presented.
Agrawal, P. K. ; Thakur, R. S.
Notes: 13C NMR shielding data for about 300 compounds are tabulated, and critical spectral features are discussed as a guide to the use of the technique in structure elucidation and stereochemical allocations of lignan, neolignan and their derivatives. Unanalysed reported data have been analysed and, wherever necessary, 13C signal assignments have been revised on the basis of more recent evidence and, to obtain consistency throughout the series.
Paz-Sandoval, M. A. ; Santiesteban, F. ; Contreras, R.
Notes: Carbon-13 NMR chemical shifts in various oxazolidines derived from pseudoephedrine and their corresponding N-borane adducts and oxazolidinium salts are examined. The observed shifts can be rationalized on the basis of steric factors, owing to the similarity between the borane adducts and the oxazolidinium salts, i.e., BH3 and CH3 appear to have the same substituent effects.
Notes: The aromatic solvent-induced shifts (ASIS) of various polar solutes induced by polar and non-polar aromatic solvents were determined. The protons that produce a large ASIS in non-polar solvents show a remarkable depression of the ASIS in highly polar aromatic solvents. The observed ASIS in polar aromatic solvents are in good agreement with the calculated ASIS based on the electrostatic interaction between solute and solvent molecules.
Chupakhin, O. N. ; Charushin, V. N. ; Chernyshev, A. I. ; [et al.] Esipov, S. E.
Notes: The structure of N-methylpyrido[2,3-b]pyrazinium salts has been examined by 1H and 13C NMR. 6-Dimethylamino- and 6-morpholino-pyrido[2,3-b]pyrazines were shown to undergo quaternization by methyl iodide at N-4 of the pyrazine ring, whereas the pyridine ring N-5 was the N-alkylation site in the reaction of unsubstituted pyrido[2,3-b]pyrazine with methyl iodide under the same conditions. The effects of quaternization on the 1H and 13C chemical shifts and the nJ(CH) values are discussed.
Guilleme, Joaquin ; Diez, Ernesto ; Bermejo, Francisco J.
Notes: The aryl carbon chemical shifts of methylbenzoic acids in CDCl3 and methylbenzoate anions in aqueous NaOH solutions have been assigned. The shifts have been interpreted by means of a model based on the additivity of substituents which is similar to that previously developed for the analysis of the methyl chemical shifts. Corrective parameters included to take into account the interactions of adjacent substituents are found to be related to both the twist angle, θ, of the carboxyl or carboxylate substituents and the conformation of the methyl groups. The derived values of the twist angle are in closer agreement with x-ray data than those estimated from UV spectra or from Cl-PPP computations.
Notes: The 1H NMR chemical shifts and spin-spin coupling constants of phenylalanylphenylalanine (Phe-Phe) dipeptide diastereomers have been completely analysed at 100 MHz. Assignment of the observed signals to individual residue protons is proposed, based on characteristic shifts and standard double resonance experiments. The rotamer populations have also been determined. The spectra of the aromatic regions of the dipeptidyl diastereomers, L-Phe-L-Phe and L-Phe-D-Phe, are very different at pH 1.95 in D2O but similar at pH 9.15 in CD3CN—D2O (34:66). These results are correlated with the retention behaviour on a C18 reversed-phase HPLC column.
Notes: The NMR spectra of eighteen 7α- and 7β-substituted 6,14-bridged thebaine derivatives are reported and the steric and other effects of the 7-substituent on the C-5-H atoms examined. Although the H-5 proton shift enabled compounds epimeric at C-7 to be distinguished in the examples studied (values falling between δ 4.75-4.40 ppm in the 7α series and δ 5.21-4.97 ppm in the 7β series), the C-5 shift values proved less useful owing to overlapping ranges.
Notes: The dynamics of the molecular rotation of 2(1H)-pyridone and 1-methyl-2(1H)-pyridone in toluene, carbon tetrachloride, methanol and water have been investigated at 305 K by 13C and 2H NMR. Both chemical shifts and relaxation times show that 2-pyridonc forms stable hydrogen-bonded complexes in methanol and in water, reorienting as a complete unit and taking with it two solvent molecules. These solvated species are stable within the liquid-state temperature range, and reorient according to the hydrodynamic law as indicated by the 14N line width measurements. It follows that the lifetimes of these complexes are always greater by at least an order of magnitude than the rotational correlation time scale. Analysis of the 14N quadrupole coupling constants and the rotational anisotropy support the structure and stability of these complexes.
Notes: Proton NMR spectroscopic studies on the conversion of 2,3-erythro-aldoses to 2,3-threo-aldoses in methanolic K2CO3 solution revealed the formation of the hemiacetals of the corresponding aldehydes, which probably provided the driving force of the easy epimerization.
Mayor, S. ; Hosur, R. V.
Notes: Long-range four- and five-bond 1H-1H coupling correlations have been observed in the dipeptide L-Lys-L-Phe by using the two-dimensional SUPERCOSY technique. Complete resonance assignments of all the non-exchangeable protons in the dipeptide have been obtained.
Mikhova, Bozhana P. ; Simeonov, Mario F. ; Spassov, Stefan L.
Notes: The vicinal 13C—1H, 15N—1H and 13C—15N spin coupling constants were obtained from the 1H and 13C NMR spectra of various ionic forms of the amino acids phenylalanine, α-aminobutyric acid and β-alanine, and also from their 15N isotopomers. It is concluded that the 13C—1H and 15N—1H coupling constants are reliable parameters for conformational studies of amino acids, whereas the practical applicability of the 13C—15N constants for the same purpose is doubtful.
Notes: The 13C resonances of the hydrate, keto and enol forms of oxaloacetic acid in aqueous solutions at low pH, at pH 4.3 and at pH 7.3 were assigned on the basis of the J(CH) values and the chemical shifts of reference compounds. At low pH the hydrate form predominated, while only small amounts of the keto and enol forms were detected. At pH 4.3 and 7.3 the keto form was the major form. In anhydrous dimethyl sulphoxide solution only the keto and enol forms were detected, whereas on addition of water the hydrate form became predominant. On prolonged recording of the spectra at the probe temperature (30°C) citroylformic acid was formed either at low pH or at pH 7-12, whereas only traces of pyruvic acid were detected. The aldol condensation product of oxalacetic acid was detected when the spectra were recorded at 7°C before its decarboxylation to citroylformic acid. In the spectra recorded at pH 3-7 pyruvic acid and its aldol condensation product, 4-hydroxy-4-methyl-2-ketoglutaric acid, were detected together with citroylformic acid. A complete assignment of the 13C resonances of these derivatives was made.
Yu. Denisov, A. ; Mamatyuk, V. I. ; Shkurko, O. P.
Notes: The proton-coupled 13C NMR spectra of 2-, 3- and 4-fluoropyridines were completely analysed and the signs and magnitudes of the 13C-1H coupling constants determined. The root mean square deviations of the observed J(CH) values from those calculated using empirical correlations between the coupling constants in monosubstituted pyridines and benzenes were found to be 0.90 Hz for 1J(CH) and less than 0.26 Hz for the other nJ(CH) couplings.
Liepinš, E. ; Birǧele, I. ; Tomsons, P. ; [et al.] Lukevics, E.
Notes: 29Si—1H coupling constants across two and three bonds in silatranes and model triethoxysilanes were measured from 1H spectra by multiple quantum NMR. There was an increase in the 29Si—O—C—H coupling in the equatorial position and a decrease in that in the axial position of the silicon trigonal bipyramid compared with the tetracoordinated silicon.
Arriaga, F. J. ; Borges-Delcastillo, J.
Notes: 13C NMR data are presented for plucheinol and its ester derivatives obtained from Pluchea odorata (L) Cass. A comparison with the data reported for cuauhtemone derivatives was carried out. An unexpected deshielding for C-4 in diester derivatives was observed.
Díaz, E. ; Domínguez, G. G. ; Mannino, A. ; [et al.] Negrón, G. ; Jankowski, K.
Notes: The assignment of the proton and carbon spectra of some cyclopropane sesquiterpene lactone derivatives of helenalin and anhydroparthenin is presented. The interpretation of the spectra was achieved using 1H-13C two-dimensional heteronuclear chemical shift correlation, proton two-dimensional homonuclear correlated 2D and 2D-J, and some classical techniques. In particular, the spectra of halocyclopropane derivatives are discussed and compared with the spectra of the parent sesquiterpenes.
Chalchat, J. C. ; Garry, R. Ph. ; Lacroix, B. ; [et al.] Michet, A.
Notes: The 13C NMR spectra of ninety-eight functionalised alkenyl and cycloalkenylcyclopropanes are described. The chemical shifts of specific carbon atoms, and the evaluation of certain pairwise contribution parameters between the substituents, provide information on the structure of the considered compounds.
Clennan, Edward L. ; Mehrsheikh-Mohammadi, M. E.

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