bluuebunny/crossref_metadata_2025_split huggingface dataset:
The structural dependence of 13C, 13C coupling constants in cyclopropanes
Authors: Stöcker Michael 
Published: May 2005

AbstractThe smallest one‐bond carbon—carbon coupling constants of cyclopropane derivatives have been measured for [1‐13C]cyclopropane‐1,1‐dicarboxylic acid and cyclopropanecarboxylic acid. The 13C, 13C coupling constants of cyclopropylcarbinol have also been determined. The dependence of 1J(CC) of the three‐membered ring on different substituents and hybridization effects is evaluated. The carbon—carbon coupling constant of the unsubstituted cyclopropane is discussed on the basis of self‐consistent perturbation theory (SCPT) and s character calculations (localized bond orbitals), and the results are compared with the experimental finding. It is shown that the 1J (CC) can be interpreted by assuming a dual‐pathway coupling mechanism.
Conformations and 13C NMR shifts in tetralins
Authors: Schneider Hans‐jörg , Agrawal Pawan Kumar 
Published: May 2005

AbstractForce field (MM2) calculations, 13C NMR substituent‐induced shifts (SIS) and epimeric shift differences (ESD) indicate a preference for equatorial substituents in the 2‐position, but equal eq/ax populations in the 1‐position of tetralines. Similar conclusions are reached from Yb(fod)3‐induced shifts, which are also used for signal assignments, e.g. in 1‐tetralone. Configurational assignments are possible for 1,2‐ and 1,3‐epimers (ESD up to 4 ppm) but, in line with the non‐discriminating eq/ax conformations at C‐I, not for 1,4‐epimers (ESD<0.5 ppm). More than 50 compounds were measured, including functional derivatives which show regular SIS for substituents in the aromatic moiety only for m‐ and p‐carbon atoms. OMe, but not OH or OAc substituents, induce o‐carbon SIS varying from −11 to −19 ppm. Conversion of 1‐hydroxytetralin to esters induces shielding variations at the aromatic carbon atoms which indicate the electrostatic origin of derivatization shifts.
14N NQR study of some local anesthetics
Authors: Buess M. L. , Bray P. J. 
Published: May 2005

AbstractNitrogen‐14 nuclear quadrupole resonance (NQR) spectra for eleven local anesthetics in the solid state are reported and analyzed using the Townes and Dailey approach. The changes in the electron distributions at various nitrogen sites, produced by protonating the tertiary amino nitrogen, are discussed and shown to be in general agreement with expectations based on the increased electrophilic character of the protonated amino group.
Conformational analogies of morphine agonists and antagonists as revealed by carbon‐13 NMR spectroscopy
Authors: Eliel Ernest L. , Morris‐Natschke Susan , Kolb Vera M. 
Published: May 2005

AbstractThe extreme similarity (except in the vicinity of the nitrogen atom) of the 13C spectra of the agonist‐antagonist pairs oxymorphone‐naloxone and morphine‐nalorphine and their respective hydrochlorides suggests that the N‐methyl and N‐allyl compounds have analogous conformations. This makes unlikely an interpretation of the agonist‐antagonist dichotomy in terms of confonnational differences. Both morphine hydrochloride and nalorphine hydrochloride exist as mixtures of two diastereomers: ca 83% of the isomer with equatorial N‐alkyl and 17% of the isomer with axial N‐alkyl (ΔG°=O.95 kcalmol−1).
13C, 77Se and 125Te NMR in ortho‐halogenated seleno‐ and telluro‐phenetoles
Authors: Baiwir Marcel , Llabrès Gabriel , Luxen André , Christiaens Léon , Piette Jean‐Louis 
Published: May 2005

Abstract77Se and 125Te chemical shifts have been measured for o‐halogenated seleno‐ and telluro‐phenetoles. Correlations exist between these parameters and the halogen electronegativities or the 13C chemical shifts, except for the fluorine derivatives. The chalcogen shifts are related to the shifts of various nuclei in halobenzene derivatives, namely 1H in benzenes, 13C in toluenes, 15N in anilines and 19F in fluorobenzenes. 77Se and 125Te chemical shifts are correlated in the o‐halogenated seleno‐ and telluro‐phenetoles and in chalcogen analogues of o‐methoxy‐selenoanisole and ‐tellurophenetole: Δδ(Te) = 1.60Δδ(Se). The observed gradient is close to values previously reported for other selenides and tellurides, but differs from the value observed in heterocycles. This observation is discussed.
Substituent effects on nuclear spin–spin carbon–carbon coupling constants in derivatives of acetylene
Authors: Kamienska‐Trela K. , Biedrzycka Z. , Machinek R. , Knieriem B. , Lüttke W. 
Published: May 2005

Abstract1J(13C13C) nuclear spin–spin coupling constants in derivatives of acetylene have been measured from natural abundance 13C NMR spectra and in one case (triethylsilyllithiumacetylene) from the 13C NMR spectrum of a 13C‐enriched sample. It has been found that the magnitude of J(CC) depends on the electronegativity of the substituents at the triple bond. The equation 1J(13C13C) = 43.38 Ex + 17.33 has been derived for one particular series of the compounds Alk3SiCCX, where X denotes Li, R3Sn, R3Si, R3C, I, Br or Cl. The 1J(CC) values found in this work cover a range from 56.8 Hz (in Et3SiCLi) to 216.0 Hz (in PhCCCI). However, the 1J(CC) vs Ex equation combined with the Egli–von Philipsborn relationship allows the calculation of the coupling constants in Li2C2 (32 Hz) and in F2C2 (356 Hz). These are probably the lowest and the highest values, respectively, which can be attained for 1J(CC) across a triple bond. The unusually large changes of the 1J(CC) values are explained in terms of substituent effects followed by a re‐hybridization of the carbons involved in the triple bond. INDO FPT calculations performed for two series of acetylene derivatives, with substituents varied along the first row of the Periodic Table, corroborate the conclusions drawn from the experimental data.
13C NMR spectra of 1,4,5,8‐tetraazaphenanthrene derivatives
Authors: Defay N. , Maetens D. , Nasielski‐Hinkens R. 
Published: May 2005

AbstractThe13C NMR spectra of 1,4,5,8‐tetraazaphenanthrene (pyrazino[2,3‐f] quinoxaline), eleven of its derivatives [2‐ and 3‐chloro, ‐methoxy and ‐(1′‐piperidino), 2,3‐dichloro, ‐dimethoxy, ‐dimethyl and ‐di(1′‐piperidino) and 9‐methoxy] and of 1,4,5,8,9,12‐hexaazatriphenylene (dipyrazino[2,3‐f: 2′,3′‐h]quinoxaline) have been assigned by {1H} selective decoupling experiments, correlations and additivities of substituent‐induced chemical shifts and proton–carbon coupling patterns. Assignments of proton spectra are extended.
Proton–proton and carbon–proton spin interactions in butatriene
Authors: Kunz R. W. , Bilinski V. , von Philipsborn W. , Dreiding A. S. 
Published: May 2005

AbstractThe proton–proton and proton–carbon coupling constants in butatriene, measured at −50°C, are reported. Signs and relative magnitudes are in agreement with the Fermi contact interaction derived from an Extended Hückel MO calculation.
1H NMR conformational analysis of disubstituted arene tricarbonyl chromium complexes
Authors: Brocard J. , Laconi A. , Couturier D. 
Published: May 2005

AbstractThe positions of conformational equilibrium in disubstituted arene chromium tricarbonyl complexes, i.e. alkylanisole chromium tricarbonyl complexes and alkylbenzoate chromium tricarbonyl complexes, have been determined by1H NMR spectroscopy. It has been found that the donor effect is the dominant factor in determining the preferred conformation.
Application of the attached proton test technique in 31P NMR spectroscopy
Authors: Jancke H. , Radeglia R. , Neels J. , Porzel A. 
Published: May 2005

AbstractIntensity modulated 31P NMR spectra were obtained using the pulse sequence published by Patt and Shoolery. This attached proton test (APT) technique for signal assignment could be applied to systems with long‐range heteronuclear couplings in POCH fragments. In a model system derived from the alcoholysis of P4S10 the six reaction products were assigned to the six signals in the 31P NMR spectrum.
13C NMR spectra of tricyclo[4.2.1.02,5]nonanes and tetracyclo[5.4.1.02,6.08,11]dodecanes
Authors: Ishii Yasutaka , Noda Toshimitsu , Kawahara Masakazu , Ogawa Masaya 
Published: May 2005

AbstractThe 13C NMR spectra of tricyclo[4.2.1.02,5]nonanes and tetracyclo[5.4.1.02,6.08,11]dodecanes and their dimethyl derivatives were measured to demonstrate the four‐membered ring annelation effects on the bicyclo[2.2.1]heptane skeleton, and the steric δ‐syn effects of the methyl groups attached to the four‐membered ring on the bridge carbons in these systems.
13C NMR spectra of p‐ and m‐substituted phenyl N‐methyl‐ and phenyl N,N‐dimethyl‐carbamates
Authors: Yamagami Chisako , Takao Narao , Nishioka Takaaki , Fujita Toshio , Takeuchi Yoshito 
Published: May 2005

Abstract13C NMR spectra of p‐ and m‐substituted phenyl N‐methylcarbamates, phenyl N,N‐dimethylcarbamates and p‐ and m‐substituted phenyl propionates were recorded, and their para 13C SCS (substituent chemical shifts) were analysed by DSP (dual substituent parameters) and DSP‐NLR (non‐linear resonance) equations. It was found that the fixed substituent Y, OCONHCH3, OCON(CH3)2 and OCOC2H5, were all mild in the sense that DSP analysis gave a good correlation, leaving little room for improvement by the DSP‐NLR treatment. Further, the three series of compounds gave similar ρI and ρR values (para derivatives, 3.2–3.3 and 17.7–18.0; meta derivatives, 5.1–5.2 and 21.8–22.0). Examination of the corresponding analyses of similar compounds indicated that the ρI and ρR values and, hence, their ratio ρR/ρR = λ, depended primarily on the nature of the atom through which the fixed substituent Y (e.g. α‐C, α‐N and α‐O) was bonded to the aromatic ring when the Y substituents are mild. The extent of this tendency for compounds with active fixed substituents is also discussed.
Conformational preferences of 2‐methoxypyridine from 1H and 13C NMR and from STO‐3G molecular orbital calculations
Authors: Blonski Wayne J. P. , Hruska Frank E. , Wildman Timothy A. 
Published: May 2005

AbstractObservable coupling over five formal bonds between the methoxy group protons and the ortho ring proton in 2‐methoxypyridine, coupliugs between the methoxy group carbon and ring protons, and methoxy carbon spin‐lattice relaxation times are all consistent with a preference for the planar cis conformer, in which conjugation is favoured and repulsions between the methyl group and the ortho hydrogen are reduced. Small‐amplitude torsioas about the C‐2–O bond may carry the methoxy group away from this orientation, but more distant conformations can probably be excluded. Methyl group rotation is less hindered in the cis than in the trans conformer. Molecular orbital calculations at the STO‐3G level, with complete geometry optimization, support the conduskus drawn from experimental evidence.
Deuterium isotope effects on 13C and 15N nuclear shielding in o‐hydroxyazo dyes
Authors: Lyčka Antonín , Hansen Poul Erik 
Published: May 2005

AbstractDeuterium isotope effects on the 13C and 15N nuclear shieldings of o‐hydroxyazo compounds are described. Both the direct and the equilibrium contributions were determined. Large direct deuterium isotope effects on 15N nuclear shieldings for 1Δ, 2Δ and 4Δ and negative Δ1J(15NH) [D] values were observed. Isotope effects on 15N nuclear shieldings, because of their magnitudes, are shown to be very useful in determining changes in the azo–hydrazone equilibrium. Isotope effects on 13C nuclear shieldings are smaller, but the effects observed at the carbon resonances of the N‐phenyl ring are likewise very useful in determining the shift in the equilibrium. Deuterium substitution leads in all cases to a shift in the equilibrium so that the content of the predominant form of the protio compound is increased.
13C NMR studies of 2,3‐dihydrofurans. Restricted rotation of bulky aryl rings in cis‐2‐aryl‐3‐methyl‐2,3‐dihydrofurans
Authors: Convert Odile , Touboul Estera , Dana Gilbert 
Published: May 2005

Abstract13C NMR spectra of some 2,3‐dihydrofurans were measured. Restricted rotation of the bulky aromatic groups of cis‐2‐aryl‐3‐methyl‐2,3‐dihydrofurans is observed when these groups have substituents in both ortho positions. Barriers to rotation were deduced from the variations in line widths of the 13C NMR signals. Exchange rates are highly affected by the buttressing effect of meta‐methyl groups.
Effects of substitution on nitrogen on barriers to rotation of amides. 2—Evaluation of the importance of resonance effects
Authors: Pinto B. Mario , Szarek Walter A. , Grindley T. Bruce 
Published: May 2005

AbstractAnalogs of N‐acetyl‐ and N‐benzoyl‐azacyclohex‐2‐enes having an oxygen atom, a methylene‐d2 group or a carbonyl group in place of the C‐4 methylene group have been synthesized. The amide rotational barriers in these compounds have been measured by the total line‐shape analysis of variable‐temperature 1H NMR spectra. The free energies of activation for both the N‐acetyl and N‐benzoyl series decrease in the sequence O≃CD2 > CO. The barriers for the first two compounds in each series are similar to those of the corresponding saturated analogs, a result which confirms recent reports that the long accepted barrier‐decreasing effect of an α‐olefinic substituent on nitrogen is counteracted. Evidence is presented that resonance stabilization of the rotational transition state in the unsaturated compounds still obtains. It is suggested that the introduction of an α‐olefinic substituent on nitrogen has a negligible effect on the amide rotational barriers in the cases of the oxygen and methylene‐d2 analogs, since any increase in the stabilization of the transition state by resonance is offset by the accompanying decrease in the sp3 character of the nitrogen atom. In cases in which a substituent on the olefinic group can interact directly with the lone pair on nitrogen, for example in the carbonyl analogs, then the resonance stabilization of the transition state is dominant.
A 17O NMR study of the protonation of urea
Authors: Valentine B. , Amour T. E. St. , Fiat D. 
Published: May 2005

Abstract17O NMR has been applied to the study of urea over a wide pH range, in fluorosulfonic acid and in magic acid (HFSO3SbF5). A 96 ppm diamagnetic chemical shift was observed on modifying the medium from an aqueous solution at pH 3 to a fluorosulfonic acid solvent. We attributed this shift to a protonation reaction at the urea oxygen having a pKa of 0.1. A 36 ppm paramagnetic shift was observed in magic acid relative to the resonance position in fluorosulfonic acid, which is consistent with the formation of a diprotonated form of urea. Values of transverse and longitudinal relaxation rates were found to be equal as a function of pH and to double on lowering the pH from 2 to −1.
Differential effects of nerve, muscle, and fat tissue on regenerating nerve fibers in vivo
Authors: Weis Joachim , Schröder J. Michael 
Published: May 2005

AbstractAxonal regeneration through silicone tubes was studied using distal nerve stumps, denervated, preatrophied muscle tissue, as well as fat tissue as a target. During the first stage of regeneration, i.e., within 2–3 weeks after surgery, a thin, filamentous structure consisting of fibrin and connective tissue‐was seen bridging the gap in all systems. Thereafter, this cord obviously served as a guideline for the outgrowth of increasing numbers of axons into distal nerve stumps as well as into muscle tissue, but not into fat tissue. These findings confirm that preatrophied muscle tissue has a similar “neurotrophic” effect on regenerating nerve fibers as distal nerve stumps. The ineffectivity of fat tissue in promoting nerve fiber regeneration could be attributed either to the absence of “neurotrophic factors” or even to an inhibitory effect.
Carbon‐13 nuclear magnetic resonance study of a new ring‐chain tautomerism of some pyridazine derivatives
Authors: Nesi Rodolfo , Chimichi Stefano , De Sio Francesco , Scotton Mirella 
Published: May 2005

AbstractThe 13C NMR spectra of a number of pyridazine derivatives have been recorded in DMSO‐d6 solution and analysed. Examination of the most diagnostic resonances, with particular emphasis on those arising from the pyridazine ring system, enabled the ready establishment of the presence of a ring‐chain tautomerism in 5‐(o‐aminophenylcarbamoyl)pyridazine‐4‐carboxylic acid, methyl 5‐(o‐aminophenylcarbamoyl)pyridazine‐4‐carboxylate, 5‐(o‐aminophenylcarbamoyl)‐3,6,‐dimethylpyridazine‐4‐carboxylic acid and 5‐(2‐amino‐1,2‐dicyanovinylenecarbamoyl)pyridazine‐4‐carboxylic acid. This gave rise to 3′,4′‐dihydro‐3′‐oxospiro[pyridazine‐5(2H),2′(1H)‐quinoxaline]‐4‐carboxylic acid, methyl 3′,4′‐dihydro‐3′oxospiro[pyridazine‐5(2H),2′(1′H)‐quinoxaline]‐4‐carboxylate, 3′,4′‐dihydro‐3′‐oxo‐3,6‐dimethylspiro[pyridazine‐5(2H), 2′(1′H)‐quinoxaline]‐4‐carboxylic acid and 5‐oxo‐2,3‐dicyano‐1,4,8,9‐tetraazaspiro[5.5]undeca‐2,7,10‐triene‐11‐carboxylic acid, respectively.
Intramolecular interactions and spin–lattice relaxation times of methyl groups
Authors: Ng Soon 
Published: May 2005

AbstractThe carbon T1 values of the alkyl substituents of various compounds have been measured. The salient observation is that the terminal methyl carbon of the n‐propyl or a three‐carbon chain bonded to an electronegative atom X(or an electron‐donating group) has a reduced T1 value. A net attractive interaction between the methyl hydrogen atoms and X in the gauche conformation is invoked to account for the observed result. In chains longer than three carbons that are not firmly anchored at one end, the γ steric interaction is suggested to be the main steric interaction that causes the reduced T1 value observed for the terminal methyl carbon.
Hindered rotation in five‐membered cyclic nitrosamines: A 13C NMR study
Authors: Haky Jerome E. , Saavedra Joseph E. , Hilton Bruce D. 
Published: May 2005

AbstractThe equilibrium rotamer populations and NN rotational barriers of N‐nitrosopyrrolidine (1), N‐nitrosothiazolidine (2), N‐nitrosooxazolidine (3) and their 2‐methyl derivatives, 4, 5 and 6, were determined by 13C NMR spectroscopy. While equal rotamer populations occur in 1 and 2, the E rotamers predominate in the other four compounds, with the highest percentage (92%) of E rotamer occurring in N‐nitroso‐2‐methyloxazolidine (6). The average barrier to NN bond rotation varies over a range of 4.1 kcal mol−1in these compounds, decreasing in the order N‐nitrosopyrrolidine > N‐nitrosothiazolidine > N‐nitrosooxazolidine. The compounds which contain an exocyclic 2‐methyl group have average rotational barriers which are 0.1–0.9 kcal mol−1 higher than those of the corresponding unmethylated derivatives. The results are interpreted in terms of the relative effects of steric hindrance by the 2‐methyl substituents and electron induction by the heterocyclic sulfur and oxygen atoms on both the rotamer populations and the NN rotational barriers.
Carbon‐13 NMR spectra of saturated heterocycles: XI—Tetrahydropyrans (oxanes)
Authors: Eliel Ernest L. , Manoharan Muthiah , Pietrusiewicz K. Michal , Hargrave Karl D. 
Published: May 2005

AbstractThe 13C NMR spectra of 62 oxanes (tetrahydropyrans) with and without methyl substituents at various ring positions, some of them bearing in addition (or instead) ethyl, vinyl, ethynyl, carbomethoxy and methylol substituents at C‐2, have been recorded, and the 294 resulting chemical shifts have been correlated by multiple linear regression analysis. Axial and equatorial α‐, β‐, γ‐, δ‐, gem‐ and vic‐parameters for shifts caused by methyl groups at all ring positions, and similar parameters for Et,—CHCH2,—CCH, CO2Me and CH2OH groups at C‐2, are reported. Standard deviations of the parameters are, in most cases, within 0.3 ppm and the agreement of calculated and experimental shifts is excellent. This is probably the largest parameter set of this type extant. 13C NMR spectra of a number of additional substituted tetrahydropyrans, and of 3,6‐dihydro‐2H‐pyrans and 3,4‐dihydro‐2H‐pyrans, are tabulated and discussed.
A revised assignment of the 13C NMR spectra of α‐ and β‐pinenes
Authors: Hall M. C. , Kinns M. , Wells E. J. 
Published: May 2005

Abstractα‐Pinene and β‐pinene 13C enriched at the C‐10 position were prepared by an unambiguous synthesis. 13C NMR spectral analysis provided evidence for a revised assignment for α‐pinene at the C‐9 and C‐10 carbon atoms.
Multinuclear two‐dimensional NMR: Assignments of natural abundance polypeptide 13C, 1H and 15N chemical shifts and demonstration of isomer interconversion
Authors: Gray George A. 
Published: May 2005

AbstractThe polypeptide carbobenzoxy‐glycyl‐L‐prolyl‐L‐leucyl‐L‐alanyl‐L‐proline (0.2 M in DMSO‐d6) was investigated using 13C, 1H and 15N NMR in natural abundance at 4.7 tesla. The existence of cis–trans‐Gly‐Pro and ‐Ala‐Pro bonds permits up to four isomers, and all four were observed (in a 60:30:7:3 ratio). 13C shifts of the proline β‐CH2 resonances are consistent only with the 60% form being trans–trans. The 30% form is either trans–cis or cis–trans (order as above) and was tentatively assigned as cis‐trans on the basis of relaxation behavior. Refocused INEPT studies aided the 13C assignments. The 15N data were obtained using both NOE and INEPT excitation, with signals evident for the three major isomers. The spectra were analysed by starting from the 13C data, which were assigned based on known regularities in peptide spectra. A 13C1H heteronuclear two‐dimensional chemical shift correlation experiment allowed direct assignment of proton shifts for major and minor isomers. The NH proton shifts were assigned by running a homonuclear two‐dimensional chemical shift correlation experiment and noting the correlation with the previously assigned α‐CH protons. The 15N resonances were then assigned from a 15N1H heteronuclear two‐dimensional chemical shift correlation experiment, relating the 15N signals directly to the NH proton resonances. Isomer interconversion between the two major isomers was demonstrated by performing a magnetization transfer homonuclear 2D experiment. Off‐diagonal intensity was noted relating the major and minor isomer alanine NH proton, as well as for the major and minor isomer leucine NH protons.
Some INDO calculations of 1J(PC) and 1J(PF) values
Authors: Duangthai S. , Webb G. A. 
Published: May 2005

AbstractINDO parameterized calculations, employing phosphorus s, p and d valence orbitals, are reported for values of 1J(PC) and 1J(PF) relating to phosphorus in formal tri‐ and pentavalent states. The 1J(PC), interactions are mainly controlled by the contact term. Thus, trivalent phosphorus compounds have negative values for 1J(PC), whereas those for pentavalent phosphorus are positive due to the s lone‐pair effect. The inclusion of phosphorus 3d orbitals is shown to be important for an understanding of the processes contributing to 1J(PF) interactions. 1J(PF) values are shown to be negative for both tri‐ and pentavalent phosphorus compounds. The contact and orbital interactions are significant for the trivalent phosphorus molecules, whereas in the pentavalent phosphorus case 1J(PF) is dominated by the orbital term.
2H and 13C NMR spectra of deuterated adamantan‐2‐ols
Authors: Duddeck Helmut , Islam Md. Rabiul 
Published: May 2005

AbstractThe composition of a mixture of adamantan‐2‐ol and its two epimeric 4‐deuterio derivatives was determined by 2H NMR spectroscopy with the aid of Eu(fod)3. In addition, unambiguous assignments of the two H‐4 signals and the two δ carbon signals were possible; these assignments had previously been speculative.