bluuebunny/crossref_metadata_2025_split huggingface dataset:
13C and 1H NMR investigation of the structure of N″‐sulphonyl‐N‐alkylideneformamidrazones
Authors: Jakobsen P. , Treppendahl S. 
Published: May 2005

AbstractThe 13C and 1H NMR spectra of N″‐sulphonyl‐N‐alkylideneformamidrazones have been recorded and the chemical shifts assigned. The tautomeric structure proved to be an N2‐ alkylidenehydrazide sulphonylimide. The barrier to rotation around the CN1 bond was estimated from variable from temperature 1H NMR measurements, and the Z/E ratio and its solvent dependence was investigated.
Investigation of substituent effects on the 1H NMR spectra of chalcones
Authors: Solčániová E. , Toma S. 
Published: May 2005

Abstract1H NMR spectra of 26 substituted chalcones (3‐aryl‐1 phenyl‐2‐propene‐1‐ones and 1‐aryl‐3‐phenyl‐2‐propene‐1‐ones) have been studied. The chemical shifts of the α and β protons to the carbonyl group were correlated with Hammett s̀ parameters. To gain information on the effect of the transmission of the resonance and inductive contributions of the substituents on the chemical shifts of H‐α and H‐β, two parameter correlations with 𝒻 and 𝓇 parameters were also perfomed. The chemical shifts of the aromatic protons of the para‐disubstituted benzene ring correlated with the ai substituent increments.
Carbon‐13 nuclear magnetic resonance spectra of ceveratrum alkaloids
Authors: Carey Francis A. , Hutton William C. , Schmidt James C. 
Published: May 2005

AbstractThe 13C NMR spectra were determined and signals assigned to the various carbons of the alkamines veracevine, germine and zygacine derived from steroidal alkaloids of the ceveratrum class. Assignment of signals was aided by analysis of the partially relaxed spectrum of cervagenine 9,12,14‐orthoacetate‐3, 16‐diacetate.
Configurational assignment by 13C NMR of stereoisomeric epoxyspirocyclohexanes derived from 4‐tert‐butylcyclohexanone
Authors: Bottin‐Strzalko T. , Roux‐Schmitt M. C. 
Published: May 2005

AbstractThe equatorial or axial configurational assignment of stereisomeric epoxyspirocyclohexanes, derived from the reaction of 4‐tert‐butylcyclohexanone with the anion of 2‐chloropropionitrile, has been determined by comparing the 13C chemical shifts of these compounds with those of the parent compounds, of known configuration, and resulting from the condensation of the anion of chloracetonitrile with 4‐tert‐butylcyclohexanone. A high field shift is observed for the cyclohexane ring carbons on going from the equatorial to the axial epoxide.
The effect of solvents on the 13C NMR chemical shifts of the carbonyl carbon and the rotational barriers of N,N‐dimethylbenzamide
Authors: Fong C. W. , Grant H. G. 
Published: May 2005

AbstractThe 13C solvent induced chemical shifts (SICS) of the carbonyl carbon and the thermodynamic barriers to rotation about the CN bond of N,N‐dimethylbenzamide are linearly related to the solvent parameter, ET(30). A multi‐parametric solvent parameter approach indicates that the SICS are influenced equally by polar effects and hydrogen‐bond donor effects. Rotational barriers for N,N‐dimethylbenzamide may, in principle, be determined by measurement of the 13C chemical shift of the carbonyl carbon in a particular solvent.
1H and 13C NMR studies of 7‐azaindole and related compounds
Authors: Cox R. H. , Sankar S. 
Published: May 2005

AbstractThe 1H and 13C chemical shifts, proton‐proton coupling constants, and one‐bond carbon‐hydrogen coupling constants have been obtained for 7‐azaindole, 1‐methyl‐7‐azaindole, their corresponding methyl iodide salts, and the related compound 7‐methyl‐7H‐pyrrolo [2,3‐b]pyridine. are different from those of either 7‐azaindole or 1‐methyl‐7‐azaindole.
Unusual carbonyl carbon chemical shifts in the 13C nuclear magnetic resonance spectra of cyclic ketones
Authors: Yates Peter , Auksi Hillar , Gosbee J. A. , Langford G. E. , Maclachlan F. N. 
Published: May 2005

AbstractThe Ketonic 13C NMR signals of a series of 6‐hydroxy‐5‐oxobicyclo[2.2.2]oct‐7‐ene‐2‐carboxylic acid lactones and of haplophytine and related N‐substituted 3‐piperidinones occur at exceptionally high field; the structural factors which are responsible have been elucidated by comparisons with related compounds.
60, 90 and 250 MHz 1H NMR spectra of sultams and sultones
Authors: Albert K.‐H. , Dürr H. , Doss S. H. , Zahra J. P. 
Published: May 2005

AbstractThe high‐field 1H NMR spectra of 1,3‐propanesultams (2), 2,4‐butanesultams (3) and 2,4‐dimethyl‐1,3‐butadienesultams (6) are reported. Comparison of 2,3 and 6 with 1,3‐propanesultone (1) and 2,4‐dimethyl‐1,3‐butadienesultone (5) reveals that the paramagnetic shift induced by the NH group is smaller than that induced by oxygen. NMR spectra at lower temperature show coupling effects with the NH proton. A half‐chair conformation was deduced for 2,4‐butanesultam from coupling constants and from a conformational analysis based on the R values, but a chair‐chair interconversion could not be detected in the temperature range between 210 and 330 K. An unambiguous assignment was carried out for the methyl signals in the spectrum of 5 by homodecoupling experiments.
A carbon‐13 NMR study of sterically hindered organotin derivatives
Authors: Axelson D. E. , Holloway C. E. , Vuik C. P. J. 
Published: May 2005

AbstractProton and 13C NMR has been used to examine a series of organotin derivatives. Anisochronous shifts are reported for chiral derivatives of tin, and 1H and 13C spin coupling constants to 117Sn and 119Sn are discussed. Spin lattice relaxation of 13C in these derivatives has been measured, and is used to indicate the effects of steric crowding on the ligands in terms of their freedom to undergo conformational rerrangements.
A novel assignment method in the 13C NMR spectroscopy of coumarins and furocoumarins
Authors: Duddeck Helmut , Elgamal M. Hanni A. , Elhady Faten K. Abd , Shalaby Nagwa M. M. 
Published: May 2005

AbstractThe signal shifts caused by replacing the carbonyl oxygen by sulphur represent a valuable method of assignment of the 13C NMR signals in coumarins and furocoumarins substituted at the benzoic and furanoic rings.
Modelling of the alkyl environment effects on the 13C chemical shift
Authors: Dubois Jacques‐Emile , Carabedian Michel 
Published: May 2005

AbstractUsing a topological parameter, λR, to characterize the effects of a variable mono or polyalkyl environment, R, on widely varied types of 13C sites gives rise to a homogeneous description of their chemical shifts over the entire range of δ13C variation (220 ppm/TMS). The proposed model, δ13C=ωcλR+ηc expresses the chemical shift in terms of this parameter together with the sensitivity, ωc, of the perturbed 13C site, bonded to a constant environment in a given family, and with ηc as the reference shift. In the case of polyalkyl environments, R=∑ Ri (n ⩽ 4); since the use of λR presupposes that groups Ri coexist in R without interacting, it is expressed as the sum of the intrinsic effects of each of these groups. Thus, this model demonstrates the general character of most of the common alkyl environment effects and the specific behaviour of the various types of 13C atoms. The homogeneity of this description relies on an assessment of the Ri contribution by the DARC/PELCO topological analysis of alkyl sites in a series of reference alkynes. The δ13C values calculated for 138 compounds, belonging to the alkane, alkene, allene, alcohol, amine, epoxide, ester and ketone families, are highly satisfactory (r̄=0.979, s̄=0.98).
High‐resolution NMR spectra of fluorene and its derivatives: VI—1‐methylfluorene, truxene and decacyclene
Authors: Drake J. A. G. , Jones D. W. 
Published: May 2005

AbstractThe overlapping spin systems in the 220 MHz 1H spectra of 1‐methylfluorene (1) in carbon disulphide and deuteriated chloroform solutions have been analysed separately and refined by LAOCOON with the aid of methyl‐ and methylene‐decoupled spectra. Ortho‐coupling constants in the 6‐membered rings are similar to each other and to those in fluorene (4). Solvent and concentration shifts suggest loose pairing of solute molecules. 220 MHz 1H spectra of α‐truxene (2) in carbon tetrachloride and deuteriated nitrobenzene, 220 MHz 1H spectra of decacyclene (3) in carbon tetrachloride, and 90 MHz FT 1H spectra of 3 in deuteriated chloroform show steric deshielding; the solvent dependence of shifts also suggests solute pairing in 2. Shifts in 1H decoupled 22.6 MHz 13C spectra of 2 in deuteriated chloroform were assigned with the aid of Cr(acac)3 relaxation agent.
Substituent chemical shift (SCS) correlations for the hydroxyl proton of substituted benzyl alcohols
Authors: Abraham Raymond J. , Bakke Jan M. 
Published: May 2005

AbstractThe hydroxyl proton chemical shift in substituted benzyl alcohols may be used, either at infinite dilution in CCl4, or in dilute solutions in DMSO, as a reliable indicator of substituent effects. The sensitivity of the hydroxyl proton to substituents is much greater than that of the methylene protons, and this is shown to be due to an increased dependence of the hydroxyl proton on the field effect of the substituent. The percent resonance contribution to the OH chemical shifts is identical in benzyl alcohols and phenols.
Application of semi‐empirical calculations of 13C chemical shifts and 1J(CH) coupling constants to the analysis of carbonium ion structures
Authors: Cheremisin A. A. , Schastnev P. V. 
Published: May 2005

Abstract13C chemical shifts and 13CH coupling constants for classical and non‐classical structures of some typical carbonium ions have been calculated by the method of summation over excited states in the INDO approximation using a special parameterization. Comparison of the data obtained with the experimental values shows that the calculation of the chemical shifts and spin‐spin coupling constants is superior to energy calculations, and provides a useful means for the study of the structure of carbonium ions.
Application of paramagnetic shift reagents to the conformational analysis of isomeric dienones
Authors: Filippova T. M. , Bekker A. R. , Lavrukhin B. D. 
Published: May 2005

AbstractParamagnetic NMR shift reagents, Eu(fod)3 and Pr(fod)3, have been applied to study the one‐ene conformations of isomeric dienones. The results obtained using various complex formation models are analysed. The preferred model suggests participation of both carbonyl oxygen Ione pairs in binding with the shift reagents. Criteria for the estimation of errors in the determination of the structure parameters of the substrate‐paramagnetic reagent complexes are suggested. The data obtained using NMR shift reagents are consistent with the existence of dienone α,β‐cis‐isomers as s‐cis‐conformers only, with the carbonyl group lying out of the plane of all the other atoms of the molecule. Both s‐cis and s‐trans conformers occur in dienone α,β‐trans‐isomers.
Nitrogen and carbon NMR of some benzofuroxans
Authors: Witanowski M. , Stefaniak L. , Biernat S. , Webb G. A. 
Published: May 2005

Abstract15N and 14N NMR spectra show that there is no valence tautomerism involving the nitro group in nitro derivatives of benzofuroxan systems and that the N‐oxide function has a fixed position in the furoxan ring. Carbon chemical shifts of molecules with one, two or three furoxan rings attached to a benzene ring reveal additivity of effects which makes possible a complete and unambiguous assignment of the shifts.
A statistical study of the additivities of substituent effects in the 13C NMR chemical shifts of hydroxy‐ and chloro‐substituted benzenes
Authors: Knuutinen Juha , Laatikainen Reino , Paasivirta Jaakko 
Published: May 2005

AbstractThe 13C NMR spectra of six hydroxybenzenes, all chlorobenzenes, all chlorophenols and eight chlorocatechols are measured and assigned. The additivity of the substituent effects and the usefulness of some corrective parameters are studied with regression analysis. The order of the chemical shifts is most efficiently predicted by the simplest substituent effect model, containing only the direct effects of the substituents, although the 95% confidence limits of the calculated shifts are as high as 5.6 ppm. If the chemical shifts need to be predicted within the measuring errors (approximately 0.05–0.10 ppm, in the present data), the number of necessary corrections is very impractical. The correction parameters are found to be independent of the solvent if no conformational effects are operative. These corrections, or the non‐additivity parameters, are thus theoretically interesting. Approximate 1J(CH) couplings are also reported and the additivity of substitution effects on these parameters are discussed.
Assignment of the 13C chemical shifts of ethidium bromide and analogs in D2O solution
Authors: Griggs Billy G. , Davidson Michael W. , Wilson W. David , Boykin David Withers 
Published: May 2005

AbstractThe 13C resonances of ethidum bromide (1), dimidium bromide (2) and 3,8‐diamino‐5‐methylphenanthridinium chloride (3) in D2O solution have been assigned. Assignments were made using fully coupled spectra, spectra obtained from a selected 180°‐τ‐90° pulse sequence in conjunction with gated irradiation to obtain NOE intensification, selective proton decoupling, chemical shift arguments and by noting the effect of pD on the 13C chemical shifts of 1 and 3.
Rotational barriers in bisadducts of 1‐cyano‐1‐methylethyl radicals with nitrones and nitroso compounds
Authors: Iwamura Michiko , Katoh Morimatsu , Iwamura Hiizu 
Published: May 2005

AbstractThe temperature‐dependent 1H NMR spectra have been measured for the bisadducts 2a and 3 of 1‐cyano‐1‐methylethyl radicals with α‐phenyl‐N‐benzylnitrone [N‐(benzylidene)benzylamine N‐oxide] and nitrosobenzene, respectively. A free energy of activation of ΔG≠ = 62.8 ∼ 64.4 kJ mol−1 (15.0 ∼ 15.4 kcal/mol) at 24 ∼ 45 °C has been obtained for 2a by applying the Eyring equation to the rate constants at the coalescence points of the methyl signals. The line shapes due to four methyl signals exchanging between two sites of equal population have been simulated by the theoretical calculation to give an activation enthalpy of 52.3 kJ mol−1 (12.5 kcal/mol) and the corresponding entropy of −39.3 J K−1 mol−1 for 3. As the inversion barriers at pyramidal nitrogens of hydroxylamine derivatives should be lowered in N‐phenyl derivatives because of conjugation, the rate process which is responsible for the observed temperature dependent NMR spectra can be assigned to restricted rotation around one of the skeletal CNOC bonds. The relevance of the results to the conformations of nitroxides derived from the spin trapping method using α‐phenyl‐N‐t‐butylnitrone [N‐(benzylidene)‐t‐butylamine N‐oxide] and nitroso spin traps is discussed.
Interproton coupling over dual vicinal and homoallylic paths in 4‐membered rings
Authors: Barfield Michael , Abia Augustine A. 
Published: May 2005

AbstractA study is presented of cis and trans HH coupling over dual vicinal (HCCH) and homoallylic/interbenzylic/interbenzylic (HCCCCH) paths in the series of molecules cyclobutene and benzocyclobutanes, and a series of dihydrocyclobutacenaphthylenes. Both the experimental and calculated molecular orbital results for these molecules increase in magnitude as the π‐bond order of the homoallylic (interbenzylic) path decreases. These trends appear to be consistent only with homoallylic (interbenzylic) coupling contributions of negative sign. At least qualitatively, these trends can be rationalized in terms of the increase in positive contributions associated with the π→π* transitions as the energy denominators decrease in the series.
13C nuclear magnetic resonance spectra of some naturally occurring friedelanones
Authors: Gunatilaka A. A. Leslie , Nanayakkara N. P. Dhammika , Sultanbawa M. Uvais S. , Wazeer Mohammed I. M. 
Published: May 2005

Abstract13C NMR spectra of friedelan, friedelan‐21‐one, friedelan‐6‐one, friedelane‐321‐dione, friedelane‐3,6‐dione and friedelane‐3,6,21‐trione have been recorded and signals assigned using off‐resonance decoupling, inversion recovery and lanthanide induced shift techniques.
The use of chiral shift reagents in an NMR study of 2,2′,6,6′‐tetrasubstituted biphenyls
Authors: Diaz E. , Rojas‐Dávila E. , Guzmán A. , Joseph‐Nathan P. 
Published: May 2005

AbstractThe determination of the enantiomeric composition of 2,2′,6′6′‐tetrasubstituted biphenyls using 1H NMR spectroscopy, in combination with chiral lanthanide shift reagents, has been studied. In general, the S compounds give largeer induced shifts than the correspondind R isomers when d‐camphor derived shift reagents are used.
13C NMR spectra of some amides and imides. Effect of inductive and mesomeric interactions, cyclization and hydrogen bonding on 13C NMR chemical shifts
Authors: Hasan Misbah Ul 
Published: May 2005

AbstractCarbon‐13 NMR chemical shifts in various amides and imides are examined. The compounds include mono‐ and diamides, acyclic imides and cyclic 5‐ and 6‐membered ring imides. The observed shifts can be satisfactorily rationalized on the basis of various electronic and steric factors which contribute to the chemical shifts in these systems. The 13C shifts in amides and imides are further compared with the shifts in corresponding oxygen analogues, i.e. esters and anhydrides. The saturated and α, β‐unsaturated amide carbonyls absorb in the range of 173–178 ppm and 167–170 ppm, respectively. These shifts are downfield by 2–3 ppm in comparison with the corresponding esters. The carbonyl shifts in cyclic imides appear in the range 170–180 ppm. In comparison with the corresponding anhydrides and amides, these shifts are downfield by 5–7 ppm and 3–4 ppm, respectively. These differences are discussed in terms of electronic interactions and steric effects.
13C NMR studies of some lupane and taraxerane triterpenes
Authors: Carpenter Roshan C. , Sotheeswaran Subramaniam , Sultanbawa M. Uvais S. , Ternai B. 
Published: May 2005

AbstractThe 13C NMR spectra of eight triterpenes are recorded and all carbon shifts have been assigned. The data are in agreement with the structures assigned to the rare lupanediol, lup‐20(29)‐ene‐3α,23‐diol, and other lupane triterpenes isolated from the Sri Lankan Glochidion species (Euphorbiaceae). The 13C NMR data of some triterpenes, aleuritolic acid derivatives and taraxerane derivatives are compared.
Linear electric field (LEF) effects in 13C NMR. Some model calculations on 5‐chloro‐1‐pentene
Authors: Van Dommelen Marianne E. , De Haan Jan W. , Buck Henk M. 
Published: May 2005

AbstractThe usefulness and some of the limitations of the linear electric field (LEF) effect in 13C NMR are illustrated by means of model calculations on the 13C NMR chemical shifts of C‐1 and C‐2 in 5‐chloro‐1‐pentene in nine different conformations. Two different concepts are used in order to calculate the electric fields near C‐1 and C‐2 caused by the C‐5Cl dipole. It is also demonstrated that, when using charges calculated by CNDO/2, the influences of the hydrogen atoms at C‐5 cannot be neglected. The use of the dipole–dipole interaction formula is advocated. The consequences of taking into account the additional contributions of the vinylic bonds to the accumulated charges at C‐1 and C‐2 are described. The results with the dipole–dipole formula show that the same signs and similar magnitudes of the LEF effects are calculated in seven out of nine conformations of 5‐chloro‐1‐pentene. This reduces the LEF to a means of confirming, rather than deducing, conformational equilibria in acylic flexible compounds. The usefulness of some recently published applications of the LEF concept to explain some short range substituent effects is critically discussed, mainly in view of the inhomogeneities of the calculated electric fields.
Low temperature 13C NMR study of 1‐(3‐pentyloxyphenylcarbamoyloxy)‐2‐dialkyl‐ aminocyclohexanes
Authors: Mlynárik V. , Beneš L. 
Published: May 2005

AbstractCyclohexane and piperidine ring reversal in 1‐(3‐pentyloxyphenylcarbamoyloxy)‐2‐dialkylaminocyclohexanes was investigated by 13C NMR. An unusually low conformational energy ΔG = 0.59 kJ mol−1 and activation parameters ΔG≠218 = 43.8 ± 0.4 kJ mol−1, ΔH≠ = 48.9 ± 2.5 kJ mol−1 and ΔS≠ = 23 ± 9 J mol−1 K−1 were found for the diequatorial to diaxial transition of the cyclohexane ring in the trans‐pyrrolidinyl derivative. In the trans‐piperidinyl derivative, ΔG222 = 44.7 ± 0.5 KJ mol−1, ΔH≠ = 55.7 ± 6.3 kJ mol−1 and ΔS≠ = 51 ± 21 J mol−1 K−1 was found for the piperidine ring reversal from the non‐equivalence of the α‐carbons.
Nitrogen‐15 nuclear magnetic resonance spectroscopy. Natural abundance nitrogen‐15 spectra of the cis and trans isomers of secondary alkylformamides
Authors: Nakanishi Hiroshi , Roberts John D. 
Published: May 2005

AbstractThe 15NMR chemical shifts were measured of a number of N‐substituted formamides and acetamides at the natural abundance level. The ratios of the cis and trans isomers for several N‐alkylformamides were also determined. Substituent effects on the 15N chemical shifts of formamides are compared with those of some other nitrogen‐containing compounds. There is a consistent pattern of behavior of the one bond spin–spin coupling constants [1J(15NH)] wherein the trans isomers of N‐alkylformamides are larger than those of the cis isomers.
(15N) acetamide in polar solvents: Hindered internal rotation and intermolecular interactions
Authors: Umemoto Kimiko , Ouchi Kenichi 
Published: May 2005

AbstractThe 1H spectrum of (15N)acetamide has been measured in dimethyl sulphoxide (DMSO), methyl propyl ketone (MPK), 1,3‐dioxane, 1,4‐dioxane, D2O, acetonitrile and pyridine‐d5 at various temperature intervals within the range of 278–343 K. From the temperature dependence of the NMR spectra of the amide protons, the free energy of activation, ΔG≠, for hindered rotation about the central CN bond was determined by means of total line shape analysis in the four solvents DMSO, MPK and the two dioxanes. Observed values of ΔG≠ (298 K) (72.7 in DMSO, 70.1 in MPK, 70.0 in 1,3‐dioxane and 70.1 kJ mol1 in 1,4‐dioxane) were not very sensitive to the choice of solvent or concentration. The concentration dependence of the internal chemical shift between the amide protons was studied in MPK, D2O, acetonitrile and pyridine‐d5. The free energy of activation and the internal chemical shift are discussed on the basis of solvent‐amide and amide–amide specific hydrogen bonding interactions, and in comparison to the results of molecular orbital calculations.
Substituent effects on 13C NMR. 2—chemical shifts in the saturated framework of secondary aliphatic derivatives
Authors: Ejchart Andrzej 
Published: May 2005

Abstract13C chemical shifts obtained under uniform conditions for selected compounds containing secondary aliphatic fragments were employed in a linear regression analysis. Two‐parameter relationships describing the substituent effects in the saturated framework were calculated, and the usefulness of such calculations is discussed. Finally, coefficients for linear relationships in primary and secondary alkyl derivatives are compared.
Structure elucidation with lanthanide induced shifts. 7—development of a reliable method for structure evaluation and the application to organic nitriles
Authors: Raber Douglas J. , Janks Christopher M. , Johnston Milton D. , Raber Nancy K. 
Published: May 2005

AbstractA useful and reliable procedure has been developed for the evaluation of the structures of organic nitriles using lanthanide shift reagents. The procedure is based on a statistical comparison of the experimental lanthanide induced shifts (LIS) with values which are predicted with the pseudocontact equation for a proposed structure. The experimental LIS are obtained by nonlinear regression analysis of the chemical shifts observed in the presence of varying amounts of the shift reagent, Eu(fod)3. The precise geometry for a proposed structure is obtained from molecular mechanics calculations. The LIS are then predicted with the pseudocontact equation using k=976.6 and a europium‐nitrogen bond length of 2.50 Å. (Detailed arguments are presented in support of these values.) The carbon‐nitrogen‐europium array is approximately linear, although small distortions from linearity are both expected and observed.