bluuebunny/crossref_metadata_2025_split huggingface dataset:
Conformational studies on 2‐fluoro‐1,2‐disubstituted ethanes by NMR spectroscopy. Influence of electronegativity on vicinal proton–proton and fluorine–proton coupling constants
Authors: Hamman Sylvain , Béguin Claude , Charlon Claude , Luu‐Duc Cuong 
Published: May 2005

AbstractThe analysis of the ABKX spectra of thirteen compounds of the series RC(H‐K)(F‐X)C(H‐A)(H‐B)X gave the four vicinal proton‐proton and fluorine‐proton coupling constants. These coupling constants of conformationally mobile structures were used (i) to calculate the populations of the rotational states of the CHFCH2 bond, (ii) to calculate the vicinal trans proton‐proton J(HH)t and gauche and trans fluorine‐proton coupling constants J(FH)g and J(FH)t and (iii) to give the unambiguous assignment of protons H‐A and H‐B. The dependence of the gauche and trans coupling constants with substituent electronegativity is explored. The results extend known correlations towards smaller electronegativity values. More quantitatively, the results and those in the literature, excluding those where deformations of torsional or bond angles occur, give a good fit of the data: a linear fit for J(HH)t = 15.0‐0.77 Σ(ΔE), an exponential fit for J(FH)g = 15.35 exp [‐0.266 Σ (ΔE)] and a linear fit for J(FH)t = 65.75 ‐ 7.52 Σ (ΔE), where Σ (ΔE) is the sum of the electronegativity difference between hydrogen and the six atoms or groups on the CHCF fragment.
Use of shift reagent with MTPA derivatives in 19F NMR spectrocopy: IV—Determination of enantiomeric composition for a variety of secondary cycloalkanols. A survey
Authors: Merckx E. M. , Lepoivre J. A. , Lemière G. L. , Alderweireldt F. C. 
Published: May 2005

AbstractChiral secondary cycloalkanols (monocyclic alcohols) are derivatized to the corresponding (R)‐α‐methoxy‐α‐trifluoromethyl‐α‐phenylacetic acid [(R)‐MTPA] esters and analysed by 19F NMR in the presence of tris(6,6,7,7,8,8,8‐heptafluoro‐2,2‐dimethyl‐3,5‐octanedionato) europium(III) [Eu(fod)3]. Using this method the enantiomeric composition can be measured for several cyclopentanols, cyclohexanols and cycloheptanols, with a variety of substitution patterns. It is shown that a mixture of four stereoisomeric cycloalkanols, such as cis and trans disubstituted alcohols, can be analysed simultaneously.
High precision NMR study of 1,1‐disubstituted silacyclobutanes
Authors: Dabbitt O. , Sutcliffe L. H. 
Published: May 2005

AbstractThe hydrogen NMR spectra of 1,1‐dimethyl‐, 1,1‐dichloro‐, 1,1‐dimethoxy‐ and 1,1‐difluoro‐silacyclobutane have been analysed. A new correlation NMR instrumental technique has been used to obtain spectral parameters with very high precision.
13C nuclear magnetic resonance and conformational analysis of 5‐chloro‐2‐oxo‐1,3,2‐dioxathianes
Authors: Gorrichon Jean‐Pierre , Chassaing Gérard , Cazaux Louis 
Published: May 2005

AbstractThe 13C NMR chemical shifts in CDCI3 for eight cyclic sulphites, chlorinated at C‐5, are reported. The α‐and β‐deshielding effects and the γ‐shielding effects for the chlorine substituent are compared with similar effects in the 1,3‐dioxane series and with the effects arising from methyl groups in the sulphite series. The study of two conformational equilibria shows that it is difficult to use 13C NMR spectroscopy for the conformational analysis of cyclic sulphites because of the frequent participation of twist forms, with 1,4‐ and 2,5‐axes, to these equilibria.
Spectral editing for 13C NMR signals of deuterated compounds
Authors: Wesener Joachim R. , Günther Harald 
Published: May 2005

AbstractJ‐modulation of 13C spin echo signals is used to develop a strategy for the analysis of deuterated compounds. On the basis of 1 J(13C2H) and an experimental set‐up that allows both 2H and 1H decoupling, 13C subspectra for various groups can be produced. The application of difference methods facilitates the analysis and, finally, leads to the identification of CD, CD2, CD3, CHD, CHD2 and CH2D groups.
Empirical additive parameter and automatic assignment of 13C NMR signals of some aryl and heteroaryl groups. A new criterion for a linear relationship between 13C chemical shifts and charge densities
Authors: Bangov Ivan P. , Radeglia Reiner 
Published: May 2005

AbstractThe 13C NMR signals of some mono‐ and disubstituted aryl compounds were assigned by means of empirical additive substituent parameters and information taken from fully coupled spectra. This assignment was compared with that obtained with the help of the method of automatic assignment of the signals based on the linear relationship between 13C chemical shift and charge density. The results show that in the cases of XR substituents (X = O, NH and R = H, CH3, CH2CH2OH) a good correlation is observed and the automatic assignment is correct. In contrast, in the cases of CH2CH2Y substituents (Y = OH, NH2, Cl) a worsening of the correlation is observed and the automatic assignment is not correct.It is suggested that for compounds with a preliminarily known assignment, the automatic assignment can serve as an additional criterion for the reliability of the linear relationship between 13C chemical shift and charge density.
Application of the selective 13C{1H} nuclear Overhauser effect to structure elucidation of photoadducts derived from maleic anhydrides and thiophene
Authors: Leon V. , Bolívar R. A. , Tasayco M. L. , Gonzalez R. , Rivas C. 
Published: May 2005

AbstractThe 13C NMR spectra of a representative series of photoadducts derived from methylmaleic anhydrides and thiophene, containing the same basic carbon skeleton, were studied in order to establish a model for future structure elucidation of similar compounds. Selective heteronuclear 13C{1H} NOE was applied to stereochemical studies on the same compounds with the dual purpose of confirming previous assignments and to gain experience in the use of this technique, rarely applied in organic chemistry. The technique was employed in two different ways, by irradiating the selected proton resonance with and without modulation [νm=½J(CH)].
Carbon‐13 magnetic resonance spectra and the stereochemistry of some substituted bicyclo[2.1.1]hexanes
Authors: Gibson Thomas 
Published: May 2005

AbstractUsing selective deuteriation and broad‐band and off‐resonance proton decoupling techniques, complete signal assignments are made for the 13C NMR spectra of a number of ketones and unsaturated esters with the bicyclo[2.1.1]hexane ring systems.
13C NMR spectra of 2,3‐dihydro‐1H‐benzo[b]azepines: Differentiation of diastereomers
Authors: Uriac Ph. , Huet J. 
Published: May 2005

AbstractThe 13C NMR spectra of 23 2,3‐dihydro‐1H‐benzo[b]azepines, including nine pairs of diastereomers separated by chromatography, [(2R*, 3R*) and (2R*), 3S*)] are hereby assigned and discussed. The relative configurations of the diastereomers were assigned by two methods. The first, based on the chemical shifts of the asymmetric carbons C‐2 and C‐3 (with regression analysis), shows that the values for (R*, R*) are approximately 1 ppm lower than those for (R*, S*) diastereomers. The second method uses the chemical shifts, δ3, of the R3(CH3) substituents. When these δ3 values are compared by means of the δ3‐δm difference (δm is the mean value obtained from compounds where R2=H), the difference is always negative for (R*, R*) and positive for (R*, S*). This is attributed to a γ‐gauche effect between R2 and R3 in the case of (R*, R*) diastereomers (R2 and R3 are cis). The results corroborate those already obtained by 1H NMR [J(23)(R*, R*)<J(23)(R*, S*)] and are a confirmation of the results of a radiocrystallographic examination carried out on two nitrogen acetylated diastereomers.
Assignment of relative configurations to acyclic diastereomeric carbinols with the lanthanide shift reagent Eu (fod)3 by 1H and 13C NMR
Authors: Ibarra C. Alvarez , Feijoo M. L. Quiroga , Perez M. S. Arias , de la Orden Parra J. 
Published: May 2005

AbstractAn assignment of relative configurations has been achieved for the diastereomeric racemates (1R2R,1S2S) and (1R2S,1S2R) of 3,3‐dimethyl‐1,2‐diphenylbutan‐1‐ol through the comparative analysis of the respective chemical shifts induced by Eu(fod)3 in the 1H and 13C NMR spectra, and the corresponding conformational distribution.
Barriers to internal rotation in 1,3,5‐trineopentylbenzenes: 10—13C and 19F NMR band shape studies and force field calculations
Authors: Andersson Sven , Drakenberg Torbjörn 
Published: May 2005

Abstract1,3,5‐Trineopentylbenzenes (TNB) with one or two benzylic substituents in each neopentyl group were synthesized. The substituents were F, Cl, Br, J, OCH3, OCOCH3, OSi(CH3)3 and CH3 and, in cases of disubstitution, F, Cl, Br, CH3 and Cl, CH3 and Br and SCH2CH2S. Barriers to internal Csp3Csp2 (aryl) and Csp3Csp3 rotation were estimated by 13C and 19F NMR band shape methods. Estimated barriers in the TNB series were found to be very close to those found for the corresponding mononeopentylbenzenes. For some of the compounds studied, molecular mechanics (MM) calculations were performed with the Allinger MMP1 program. Differences between calculated and experimental estimated barriers were found, and possible sources of these discrepancies in terms of parameters used in the MMP1 program are discussed.
Ab initio MO calculations and 17O NMR at natural abundance of para‐substituted acetophenones
Authors: Brownlee Robert T. C. , Sadek Maruse , Craik David J. 
Published: May 2005

Abstract17O NMR chemical shifts and calculated (ab initio MO theory) electron densities are reported for a series of para‐substituted acetophenones, XC4H6COCH3, where X = NH2, OCH3, F, Cl, CH3, H, COCH3, CN, NO2. The 17O shifts are very sensitive to the para substituent and cover a range of some 51 ppm. Donors induce upfield shifts and acceptors downfield shifts. The substituent chemical shifts (SCS) correlate precisely with σI and σR+ using the Dual Substituent Parameter (DSP) method. The derived transmission coefficients ρI and ρR indicate that polar and resonance mechanisms contribute approximately equally to the observed substituent effects. The shifts also correlate well with calculated π‐electron densities (slope = 1500 ppm per electron) confirming their electronic origin. λ values are also reported, and the role of the average excitation energy, ΔE, in determining 17O SCS values is discussed. It is concluded that variations in ΔE are minor and that the local Δ‐electron density is the dominant feature controlling 17O SCS values.
Nitrogen‐15 NMR studies of 1,4‐benzodiazepines: 1
Authors: Scahill Terrence A. , Smith Stanford L. 
Published: May 2005

AbstractNitrogen‐15 NMR data are reported for ten benzodiazepines, including the chemically useful drugs diazepam, oxazepam, clonazepam, flurazepam and chlordiazepoxide. Substituent effects for neighboring groups are presented and discussed.
13C NMR assignments of nonionic and anionic ethoxylated surfactants
Authors: Figdore Phillip E. 
Published: May 2005

Abstract13C chemical shift assignments have been made for the ethoxy region of nonionic and anionic ethoxylated surfactants. The lanthanide shift reagent Eu(fod)3 was used to assign the shifts of nonionics because of some ambiguities in the literature.
Conformational analysis of 7‐membered dimethyl cyclic sulphites: 2‐Oxo‐1,3,2‐dioxathiepanes and 3‐oxo‐2,4,3‐dioxathiepins
Authors: Guimaraes Afonso Celso , de Almeida Paulo Gontijo Veloso , Baltas Michel , Cazaux Louis 
Published: May 2005

Abstract2‐Oxo‐1,3,2‐dioxathiepanes and 3‐oxo‐2,4,3‐dioxathiepins, including two series of three diastereoisomers, were synthesized, isolated by HPLC and characterized by 1H and 13C NMR spectroscopy. Their conformational behaviour was studied using a computer‐assisted LIS technique and, for c‐4, t‐7‐dimethyl‐2‐oxo‐1,3,2‐dioxathiepane, a 400 MHz spectral analysis. Single twist‐chair conformations or an equilibrium between them are the most stable in the dioxathiepane series while chair or twist‐boat forms, or both in equilibrium, are favoured in the dioxathiepin series. Conformations and equilibria are detailed, with and without LSR, taking into account 1H coupling constants and IR SO stretching frequencies as conformational probes.
The NMR spectra of the porphyrins: 24—The NMR spectra of some tetraarylchlorins
Authors: Abraham Raymond J. , Plant James E. , Bedford Geoffrey R. 
Published: May 2005

AbstractThe synthesis and complete assignment of the 1H NMR spectra of 5‐(o‐pivaloylaminophenyl)‐10,15,20‐triphenylporphyrin (PIVTPP) and its two chiral dihydro adducts 3,4‐dihydro‐(PIVPTPC‐I)‐ and 7,8‐dihydr‐ (PIVPTPC‐II)‐porphyrins are reported. The use of the zinc complexes of the chlorins as chiral shift reagents with optically active bases is discussed. Comparison of the observed shift differences between the chlorins and the parent porphyrin with those calculated by a ring current model shows that a decrease in the ring current occurs on chlorin formation, and also specific effects occur at the reduced pyrrole ring, presumably reflecting different steric constraints.
Mass spectrometry in structural and stereochemical problems. Part CLIII. Electron impact‐promoted fragmentation of n‐alkyl cyanides
Authors: Carpenter Wayne , Sheikh Younus M. , Duffield A. M. , Djerassi Carl 
Published: May 2005

AbstractIn spite of previous extensive studies on the mass spectrometry of alkyl cyanides, no good mechanistic insight has as yet been gained into the behavior of straight chain alky1 cyanides. For this reason the possible origins for the principal ions in the mass spectrum of a typical alkyl cyanide (n‐hexyl cyanide) have been determined using high resolution mass spectrometry anddeuterium labeling of every carbon atom. The results lead to the conclusion that most of the typical fragmentation processes of n‐alkyl cyanides proceed through cyclic intermediates.
Mass spectrometric studies of cycloalkane‐α‐glycols
Authors: Sasaki S. , Itagaki Y. , Abe H. , Nakanishi K. , Suga T. , Shishihori T. , Matsuura T. 
Published: May 2005

AbstractThe mass spectral fragmentations of stereoisomeric cyclohexane‐1,2‐diols, p‐menthane‐2,3‐diols, 1‐hydroxycarvomenthols and 4‐hydroxymenthols are discussed.
Skeletal rearrangements in mass spectra. Part I. Bis‐aryl compounds
Authors: Wszolek P. C. , McLafferty F. W. , Brewster J. H. 
Published: May 2005

AbstractExamination of a large number of spectra indicates that bis‐unsaturated compounds commonly undergo a skeletal rearrangement in which part or all or the bridging moiety is eliminated, often with concomitant loss of hydrogen atoms. The spectra of labeled azobenzene, diphenyl sulfide, and their p,p′‐dimethyl derivatives show that scrambling of hydrogen atoms precedes or accompanies such rearrangements, in contrast to the loss of a p‐methyl group from the latter derivatives. These results are rationalized in terms of the radical site formed on one unsaturated functional group attacking the polarizable π‐electrons of the other unsaturated group.
‘Mass spectrometry of vitamin B6: Different forms of the vitamin, its metabolites, antimetabolites, and analogs’
Authors: Dejongh D. C. , Perricone S. C. , Gay M. L. , Korytnyk W. 
Published: May 2005

AbstractThe mass spectra of the different forms of vitamin B6, some metabolites and antimetabolites, and some analogs are reported. The free bases are suitable for study, but the 5‐phosphates are not sufficiently volatile. The hydrochloride salts dissociate thermally in the inlet system into the free base and HCl and give the spectrum of the free base with the spectrum of HCL superimposed on it. The compounds studied are: pyridoxol, pyridoxamine and pyridoxal, which are different forms of vitamin B6; 4‐pyridoxic acid and its lactone, 5‐pyridoxic acid lactone, isopyridoxal, 5‐formyl‐3‐hydroxy‐2‐methylpyridine‐4‐carboxylic acid, and 3‐hydroxy‐2‐methylpyridine‐4,5‐dicarboxylic acid, which are vitamin B6 metabolites; α4‐and α5‐deoxypyridoxol, 3‐deoxypyridoxol, and 4‐ and 5‐ norpyridoxol, which are antimetabolites and analogs of vitamin B6.
Amino‐acid sequence study in peptides by mass spectometry—III Investigation of ethyoxycarbonyl‐peptide methyl esters
Authors: Kamerling J. P. , Heerma W. , Vliegenthart J. F. G. 
Published: May 2005

AbstractThe utility of ethoxycarbonyl‐peptide methyl esters for mass spectrometric analysis is described. The ethoxycarbonyl group has important advantages over other protecting groups which are in use. The derivatives have high intensity; this greatly facilitates the interpretation of the fragmentation pattern. The spentra of the methyl esters of the ethoxycarbonyl derivatives of pro‐val, trp‐gly, gly‐ser, (cys)2, glutation (GSH), glu‐his‐phe, val‐tyr‐pro and val‐lys‐val‐tyr‐pro are given.
Effects related to Stevenson's rule in mass spectral intensity correlations
Authors: Bursey Maurice M. , Wolfe Edward S. 
Published: May 2005

AbstractAccording to Stevenson's rule, there is a possibility that the chloromethyl and bromomethyl ions in the spectra of alkylhalides may not be formed from the molecular ion by processes described by electronic ground states alone. Since ion intensities at 75 eV are generally considered to be governed by appearance potentials, the operation of Stevenson's rule should influence correlations of intensity data according to the kinetic approach to mass spectra. Deviations from linearity were obtained in correlations of CH2Br+ intensities, but not in those of CH2CL+. Stevenson's rule is of help in explaining the deviations, but by its nature it is not absolute in predicting their occurrence with certainty. Consequently caution must be exercised in the interpretation of new data, particularly for aliphatic compounds.
The mass spectra of some C‐19 modified cholesteryl derivatives
Authors: Kirkien‐Konasiewicz Alijca M. , Moriarty Robert M. , Loudon Alexander G. , Cardnell Peter M. 
Published: May 2005

AbstractThe mass spectra of twenty one C‐19 modified cholesteryl derivatives have been determined and compared with results for related systems. In the case when the hydrogen(s) of the C‐19 group have been replaced by other groups the metastable evidence shows that in those molecules with a C‐3 hydroxyl group the loss of water followed by the loss of the C‐19 group gives rise to an intense ion at m/e 353, whereas the loss of the C‐19 group with hydrogen transfer to the ion, followed by the loss of water gives rise to the large ion at m/e 354. In contrast in the case of the C‐3 acetates the main fragmentation is the loss of acetic acid followed by the loss of the C‐19 group to give the ion at m/e 353. This is rationalised on the basis of results observed in other systems. In the case of the C‐3 tosylates evidence for pyrolysis before electron impact fragmentation is presented. The subsequent fragmentation of the large ions at m/e 354, 353 and other m/e values in the high mass region is shown to be in line with earlier work.
Computer‐aided interpretation of mass spectra
Authors: Venkataraghavan R. , McLafferty F. W. , van Lear G. E. 
Published: May 2005

AbstractA system is described in which computer techniques are used to carry out major steps in the procedure for interpretation of high‐resolution mass spectral data. These steps include identification and evaluation of the molecular ion, neutral fragments lost from the molecular ion, and characteristic ion series, followed by elucidation of specific structural details using a sub‐routine for the particular compound class selected. The technique shows promise of not only increasing the interpreter's efficiency, but of providing more specific and detailed structural information from the spectral data.
Mass spectra of indazolones and pyrazolones—I: Indazolones
Authors: Desmarchelier J. M. , Johns R. B. 
Published: May 2005

AbstractThe mass spectral fragmentations of 3‐indazolone (I), 1‐acetyl‐3‐acetoxyindazol (II), 1,2‐diacetyl‐3‐indazolone (III), 1‐methyl‐3‐indazolone (IV), 2‐methyl‐3‐indazolone (V), 2‐methyl‐3‐indazolone‐N‐d‐1 (VI), 3‐methoxy‐indazole (VII), 1‐ethyl‐3‐indazolone (VIII), 1‐carbethoxy‐3‐indazolone (IX), 1‐carbethoxy‐2‐methyl‐3‐indazolone (X), 2′‐carboxyethyl‐3‐indazolone (XI), 1‐oxo‐2,3‐dihydropyrazolo‐(1,2‐α)‐3‐indazolone (XII) and 1‐ethyl‐3‐indazolone‐N‐d‐2 (XIII) are reported. The loss of an ·N2R radical from the parent radical ion in indazolone and the alkyl indazolones occurs more readily than the loss of a formyl radical, and no loss of HCN is observed from the parent radical ion. Mass spectral data can be used to distinguish between N‐methyl and O‐methyl derivatives of 3‐indazolone.
The elimination of small neutral molecules and fragments in mass spectra—II: 2‐substituted 8‐hydroxyquinolines
Authors: Stevenson Robert L. , Wacks Morton E. , Scott Ward M. 
Published: May 2005

AbstractThe mass spectra of a series of 2‐substituted 8‐hydroxyquinolines and related compounds are reported. Fragmentation pathways based upon interpretation of spectra and metastable transitions for 8‐quinolinol; 2‐methyl‐8‐quinolinol; 4‐methyl‐8quinolinol; 2‐hydroxymethyl‐8‐quinolinol; 2‐aminomethyl‐8‐quinolinol; 8‐quinolinol‐2‐carboxaldehyde; 8‐quinolinol‐2‐carb‐oxaldehyde oxime; and 8‐quinolinol‐2‐carboxaldehyde tert‐butylimine are discussed, as are dissociations in the related compounds 2‐hydroxymethyl quinoline and quinoline‐2‐carboxaldehyde oxime. It is suggested that the molecular ions of 2‐substituted‐8‐quinolinols undergo rearrangement to a substituted azatropylium ion prior to dissociation. An ion of m/e 89 has been observed in these spectra and is considered to be characteristic of the quinoline nucleus bearing an X‐substituent in any position, where X  OR, SR, NH2 etc. (R  H, CH3, etc).
Mass spectra of isomeric monoalkylanisoles and monoalkylphenols with straight alkyl chains
Authors: Gorfinkel M. I. , Ivanovskaia L. Yu. , Koptyug V. A. 
Published: May 2005

AbstractAn analysis of the mass spectra of ortho, meta and para isomers of monoalkylanisoles and monoalkylphenols, the alkyls being n‐amyl, n‐octyl and n‐undecyl, has been performed. The regularities found allow determination of the structure of such compounds by inspection of the mass spectrum only. It was shown that Hammett's equation may be used for evaluating a ration of intensities of peaks originating formally from the simple β‐cleavage and that accompanied by hydrogen migration of the resulting fragment ions.
Electron‐impact induced fragmentation of 2‐substituted 2H‐cyclopenta[D]pyridazines
Authors: Forkey David M. 
Published: May 2005

AbstractThe mass spectra of the non‐benzenoid aromatic heterocycles 2H‐ and 2‐methyl‐2H‐cyclopenta[d]pyridazine and several deuterated analogs have been analyzed. The majority of the nitrogen lost from these heterocycles occurs as HCN OR H2CN. The deuterium labeling suggests a rearrangement of the molecular ion prior to fragmentation.
The loss of water from molecular ions of aliphatic ketones in electron‐impact mass spectra
Authors: Yeo Adrian N. H. , Williams Dudley H. 
Published: May 2005

AbstractIn a series of straight chain aliphatic ketones which has been studied, it has been shown that the structural requirement for loss of water from the molecular ions produced by electron‐impact is an alkyl group of seven or more carbon atoms attached to the carbonyl function.