bluuebunny/crossref_metadata_2025 huggingface dataset:
1H NMR study of cis‐trans isomerization in two analogs of the thiol form of thiamine
Authors: Chriss Derald , Miller Robert H. , Echols Richard E. , Vessel Ellen
Published: May 2005

Proton magnetic resonance (1H NMR) was used to study cis‐trans isomerization in N‐methyl‐N‐(1‐methylthio‐2‐propenyl)formamide and N‐benzyl‐N‐(1‐methylthio‐2‐propenyl)formamide, two analogs of the thiol form of thiamine. Benzene dilution studies and shift reagent studies were used to make resonance assignments, which indicate that the predominant isomer for each analog has the CC bond trans to the carbonyl oxygen. Shift reagent studies, using Pr(fod)3 in CCl4 or CDCl3, suggest that the reagent may be bonding to both the nitrogen and oxygen atoms of the substrate. For some of the systems studied, varying ρ at constant temperature had the same spectral effect as varying temperature at constant ρ.
Carbon‐13 NMR studies of Ni(II) porphyrin and chlorin complexes
Authors: Ulman Abraham
Published: May 2005

The 13C NMR spectra of tetraalkyl‐porphyrin and ‐chlorin complexes of nickel(II) were studied. The 13C NMR of (5,10,15,20‐tetramethylchlorinato)nickel(II) supports the model of asymmetric charge distribution in this chlorin, as derived from the structure analysis and from previous proton NMR studies.
A two‐dimensional NMR study of angelic and tiglic acid
Authors: Joseph‐Nathan P. , Wesener J. R. , Günther H.
Published: May 2005

The controversy about the 13C NMR assignment of the methyl groups in angelates and tiglates was settled by two‐dimensional 1H13C chemical shift correlations for angelic and tiglic acid.
Carbon‐13 NMR spectra of isocoumarin, N‐methyl‐1(2H)‐isoquinolinone and related compounds
Authors: Spassov S. L. , Atanassova I. A. , Haimova M. A.
Published: May 2005

The 13C NMR spectra of isocoumarin, N‐methyl‐1(2H)‐isoquinolinone and 14 of their 3‐ and/or 4‐substituted derivatives were measured and assigned with the aid of various spectral techniques. The values of the one‐bond and some of the long‐range 13C‐13C‐1H coupling constants are reported. The effect of substitution on the 13C chemical shifts is discussed.
A 15N NMR investigation of some azolopyridines
Authors: Stefaniak L. , Roberts John D. , Witanowski M. , Hamdi B. T. , Webb G. A.
Published: May 2005

15N NMR chemical shift data are presented for 14 azolopyridines, together with the results of INDO/S‐SOS calculations of nitrogen shieldings. Previous 14N NMR results for some of these compounds are reinterpreted. The 14N data and their assignments are shown to be reliable for the indolizine nitrogen atom from arguments based on relative line widths. The pyridine‐type nitrogens are more reliably assigned from the 15N spectra combined with the results of the INDO/S‐SOS calculations for individual molecules. A combination of 14N and 15N NMR spectra, together with the shielding calculations, provides a basis for unambiguous assignments of all the various nitrogen environments considered.
A 13C and 1H NMR study of diastereomeric α‐methylidene‐β‐hydroxy‐γ‐alkoxy esters
Authors: Banfi Luca , Potenza Donatella , Ricca Giuliana Severini
Published: May 2005

The 13C and 1H NMR spectra of α‐methylidene‐β‐hydroxy‐γ‐alkoxy‐pentanoates and ‐decanoates are presented. These data are consistent with a preferred conformation in which an intramolecular hydrogen bond is present. Very characteristic steric shifts in the 13C and 1H NMR spectra provide an efficient tool for the configurational assignment for this class of compounds.
33S chemical shifts and line widths of selected sulphones, sulphoximides, sulphimides, sulphides and sulphonium ions
Authors: Annunziata Rita , Barbarella Giovanna
Published: May 2005

The 33S chemical shifts, δ, and the line widths of selected sulphones, sulphoximides, sulphimides, sulphides and sulphonium ions were measured at 23.009 MHz. δ increased with decreasing electronic charge on sulphur. The line width varied from 3–10 ppm for sulphones to 400 ppm for sulphonium ions. The higher geometrical flexibility of five‐membered ring sulphones with respect to the six‐membered ring compounds was reflected in the variations of δ with methyl substitution. Open‐chain sulphoximides are shielded with respect to the corresponding sulphones, whereas open‐chain sulphimides are deshielded with respect to the corresponding sulphoximides.
Effect of molecular motion and solvent interactions on nitrogen‐15 relaxation in anilines
Authors: Lambert Joseph B. , Stec Daniel
Published: May 2005

Dipolar relaxation of 15N in anilines and anilinium ions is influenced by overall motion of the molecule, by rotation about the aryl–‐nitrogen bond, by inversion of the aniline nitrogen and by interactions of the NH2 or NH3+ group with the solvent. These factors are assessed by comparison of the 13C and 15N dipolar relaxation times as a function of para‐substitution on the aryl ring. In the anilines (solvent CDCl3), electron withdrawal brings about faster relative motion of the amine side‐chain, contrary to expectation from consideration of CN rotation but in agreement with the effects from nitrogen inversion. The 15N dipolar relaxation time correlates with the Hammett σp. For the anilinium ions (solvent Me2SO‐d6), there is no correlation with σp and no qualitative relationship with either CN rotation or N inversion. Nitrogen‐15 relaxation, corrected for overall motion as judged by ring 13C relaxation, correlates with the inductive parameter σI. Electron withdrawal through induction reduces hydrogen bonding and increases side‐chain mobility. For most of the anilines and for all of the anilinium ions, solvent interactions cause the nitrogen side‐chain to be less mobile than the aryl ring. Under these circumstances, the Woessner approach cannot be used to calculate barriers. The hydrogen bond donor properties of the anilines are reduced in the absence of electron‐donating substituents, and the first barriers to NH2 rotation/inversion were calculated by this procedure: aniline in CDCl3 3.5 kcal/mol, p‐chloroaniline in CDCl3 3.4 kcal/mol and p‐nitroaniline in acetone 3.8 kcal/mol.
Two‐dimensional NMR studies of cyperene
Authors: Joseph‐Nathan P. , Martińez E. , Santillan R. L. , Wesener J. R. , Günther H.
Published: May 2005

Combined utilization of 1H1H homonuclear and 1H13C heteronuclear NMR chemical shift correlations, two‐dimensional J‐resolved 1H NMR measurements and homonuclear 1H double resonance experiments allowed specific assignments for both 1H and 13C NMR frequencies to be made for the tricyclic sesquiterpene cyperene. The results also provided information on the conformation of the six‐membered ring of this natural product, which was recognized as a distorted chair.
13C and 1H NMR spectral studies of N‐alkylmethylquinolinium salts
Authors: Jaroszewska Jolanta , Wawer Iwona , Oszczapowicz Janusz
Published: May 2005

13C and 1H chemical shifts of fourteen N‐alkylmethylquinolinium salts in DMSO‐d6 are reported, and compared with those of the eleven corresponding methylquinoline bases. The influence of ring substitution by methyl groups in the salts and substitution at the nitrogen atom and the effect of the anion are discussed.
Luminescent metal complexes. 4—13C NMR spectra of the tris chelates of substituted 2,2′‐bipyridyls and 1,10‐phenanthrolines with ruthenium(II) and osmium(II)
Authors: Cook Michael J. , Lewis Anthony P. , McAuliffe Glenn S. G.
Published: May 2005

13C Chemical shifts are reported for the ruthenium(II) tris complexes of thirteen 2,2′‐bipyridyls and three 1,10‐phenanthrolines and for the osmium(II) tris complexes of five 2,2′‐bipyridyls. Chelation induced shifts (δcomplex – δligand) are discussed in terms of models for π back‐bonding. 13C NMR is shown to be a convenient tool for the direct observation of the geometrical isomerism of complexes formed from monosubstituted ligands.
Glucosidation shifts of allylic and benzylic alcohols in 13C NMR spectroscopy
Authors: Horibe Isao , Seo Shujiro , Yoshimura Yohko , Tori Kazuo
Published: May 2005

The 13C FT NMR spectra of β‐D‐glucopyranosides (including their tetraacetates) of several secondary allylic and benzylic alcohols were compared with those of methyl β‐D‐glucopyranoside and the corresponding parent alcohols. The characeristic glucosidation shifts observed for these alcohols may be applicable to the determination of the absolute configuration of the hydroxy group in these alcohols.
1H, 13C and 15N NMR spectra of [1,2‐15N2]pyrazole derivatives
Authors: Fruchier Alain , Pellegrin Valdo , Claramunt Rosa Maria , Elguero Jose
Published: May 2005

The chemical shifts and coupling constants of [1,2‐15N2]pyrazole, 2‐(1‐[1,2‐ 15N2]pyrazolyl)‐2‐[l,3‐2H6]propanol, 1‐nitro[1,215N2] and 3‐nitro[1,2‐15N2]pyrazole are reported.
Magnetic resonance study of diastereomeric interactions of nitroaromatic sulfxides with alcohols in solution
Authors: Sweeting Linda M. , Anet Frank A. L.
Published: May 2005

The synthesis of optically active (1R,2R)‐ and (1S,2R)‐2‐deuterio‐2,3‐dihydro‐2‐methyl‐6‐nitrobenzothiophene‐1‐oxide (3 and 4) is described. Several racemic aryl methyl carbinols in the presence of 3 or 4 give different chemical shifts for enantiomeric CH, CH3 and OH protons. These chemical shift differences are larger than those observed in analogous sulfoxide–alcohol pairs without nitro groups. Quinine and cinchonidine cause observable non‐equivalence of methylene and aromatic protons in racemic 4. The magnitude of the diastereomeric shift difference is sensitive to temperature, solvent, concentration, nature of the π system and steric effects.
Stereochemical study of hindered α‐glycols by 1H and 13C NMR spectroscopy
Authors: Pascal Y. , Convert O. , Berthelot J. , Fournier F.
Published: May 2005

Sterically hindered α‐glycols, obtained from electrochemical hydrodimerization of polycyclic ketones (indanone, tetralone, chromanone, flavanone, xanthone and fluorenone), were studied by 1H and 13C NMR. Evidence of conformational hindrance was deduced from the 1H spectra; meso or racemic configurations and the conformational stereochemistry of these molecules in solution were assigned.
Stereostructure of condensed‐skeleton cis‐ and trans‐dihydro‐1,3‐thiazines and 1‐thia‐3‐azaspiroalkenes
Authors: Sohár P. , Simon L. , Bernáth G.
Published: May 2005

The stereostructures of some condensed‐skeleton cis‐ and trans‐dihydro‐1,3‐thiazines and 1‐thia‐2‐phenyl‐3‐azaspiro[4n + 1]alk‐2‐enes (n = 3–6) were established by 1H and 13C NMR spectroscopy. A comparative study indicated that the cis‐thiazines have greater conformational mobility than the corresponding oxazines, although the preferred conformer of the two types of cis compounds is the same, with the sulphur axial and the 4‐methylene group equatorial relative to the rings.
13C NMR spectra of 3‐substituted phlorophenone compounds
Authors: Dekker Theodor G. , Fourie Theunis G. , Snyckers Friedrich O. , van der Schyf Cornelis J.
Published: May 2005

The 13C NMR spectra of a series of 3‐allyl‐, 3‐prenyl‐ and 3‐benzyl‐phlorophenone compounds are reported. Relative substituent effects are discussed.
Determination of the conformation of diethylmethyl‐2‐[p‐(o‐propoxybenzamido)benzoyloxy]ethylammonium bromide in solution by measurement of selective proton spin–lattice relaxation rates
Authors: Sega Alessandro , Ghelardoni Mario , Pestellini Vittorio , Pogliani Lionello , Valensin Gianni
Published: May 2005

The relative conformation of the aromatic rings and the amide bridge of diethylmethyl‐2‐[p‐(o‐propoxybenzamido)benzoyloxy]ethylammonium bromide has been established by a combined analysis of non‐selective, single‐selective and double‐selective pulse experiments using, as a basis of comparison, the Dreiding molecular model of the compound.
High‐resolution 13C NMR studies of solid 1,4‐bis(n‐butylamino)anthraquinone
Authors: Harris R. K. , Jonsen P. , Packer K. J.
Published: May 2005

High‐resolution 13C NMR spectra of solid 1,4‐bis(n‐butylamino)anthraquinone are presented. In spectra measured at 22.6 MHz the effects of two short‐range and two long‐range residual (13C, 14N) dipolar couplings have been observed. Only the short‐range effects are observable in the 50.3 MHz spectra. These typical asymmetric doublets allow the determination of the 14N nuclear quadrupole coupling constant (χ=e2Qq/h=−3.0 MHz), the asymmetry parameter (η=0.3) and the orientation of the electric field gradient tensor of the 14N in the molecular framework.
Ring finger testing in carpal tunnel syndrome: A comparative study of diagnostic utility
Authors: Uncini Antonino , Lange Dale J. , Solomon Murray , Soliven Betty , Meer Jacob , Lovelace Robert E.
Published: May 2005

Because digit 4 (D4) has dual innervation, median and ulnar sensory latencies can be determined over identical distances. To determine if D4 testing is more sensitive than other commonly used techniques to diagnose carpal tunnel syndrome (CTS), we examined 42 hands with clinical evidence of carpal tunnel syndrome and 43 control hands. D4 latency was significantly longer than controls more often than digit 2 (D2) in patients with CTS. Comparing median to ulnar latencies from D4 was the most sensitive method to make the diagnosis of CTS. in mild CTS, a characteristic double peak potential was seen in recordings from the median nerve after stimulating D4. This potential provided immediate visual confirmation of the diagnosis of CTS. Comparing D4 latency along median and ulnar nerves is useful for detecting mild CTS and should be used whenever there are clinical signs and symptoms of CTS but electrodiagnostic studies are normal or borderline.
Proton and carbon‐13 nuclear magnetic resonance studies of substituted pyridines and pyrimidines: VII—The structure of hydroxy‐ and mercapto‐ pyridines and pyrimides from J(HH) and J(CH) values
Authors: Vitorge M. C. , Chenon M. T. , Coupry C. , Lumbroso‐Bader N.
Published: May 2005

Accurate values of iJ(HH) and iJ(CH) were obtained for a series of hydroxy‐and mercaptopyridines and‐pyrimidines. It is shown that the 3J(CH) values provide a valuable criterion for differentiating aromatic from quinoidal structures, and is an easy method for determining N‐methylation or N‐addition sites.
Long‐range shielding by cyclopropyl groups in 10‐spirocyclopropyl‐9,10‐dihydroanthracenes
Authors: Ryder Mary T. , Rosenfeld Stuart M.
Published: May 2005

The peri protons in a series of 10‐spiroclopropyl‐9,10‐dihydroanthracenes have been shown to have shifts consistent with large (0.43‐0.55 ppm) long‐range shielding effects exerted by neighboring cyclopropyl groups. The shieldings are expected to be sensitive to variations in preferred conformation and, since the range of observed shifts for the five compounds studied is relatively small, it is concluded that all exhibit similar conformational preference.
NMR evidence for planar chirality in natural porphyrins
Authors: Gaudemer A. , Gaudemer F. , Merienne C.
Published: May 2005

The 1H NMR spectra of several six‐coordinate cobalt(III) porphyrins of general formula L2Co(DPDME)CI, where DPDME=deuteroporphyrin dimethyl ester and L is an optically active ligand, have been measured at 250 or 400 MHz. In a few cases, two signals of equal intensity are observed for the L ligand protons. This magnetic non‐equivalence, which never exceeds 0.04 ppm, is thought to arise from the planar chirality of the porphyrin ring, which makes a proton in the ligand L above the porphyrin ring and the corresponding proton below this ring diastereotopic.
17O NMR spectra of equatorial and axial hydroxycyclohexanes and 5‐hydroxy‐1,3‐dioxanes and their methyl ethers
Authors: Eliel Ernest L. , Liu Kwang‐ting , Chandrasekaran Subramanian
Published: May 2005

17O chemical shifts of axial hydroxyl groups in cyclohexanols are upfield of those of corresponding equatorial groups, but in 5‐hydroxy‐1,3‐dioxanes the opposite is observed: the axial OH resonates downfield of the equatorial OH. The situation is the same in the corresponding methyl ethers and is, thus, not a result of intramolecular hydrogen bonding in the axial 5‐hydroxy‐1,3‐dioxane, but appears to parallel the effect on 13C and 19F shifts observed in corresponding equatorial and axial 5‐methyl‐ and 5‐fluoro‐1,3‐dioxanes, which has been attributed to an upfield shifting effect of the antiperiplanar γ‐located heteroatoms. Surprisingly, the reciprocal effect is not seen in the ring 17O shifts of the 5‐hydroxy‐1,3‐dioxanes. A δ compression shift is seen in the 17O spectrum of trans‐3,3,5‐trimethylcyclohexanol (syn‐axial OH and CH3), analogous to the effect earlier reported in 13C spectra. Conversion of four of the alcohols to methyl ethers produces a large upfield effect on the 17O shift, larger in the cyclohexanols than in the 1,3‐dioxane‐5‐ols. Similar upfield shifts have been recorded in the literature; their extent depends on whether the alcohols are primary, secondary or tertiary.
ESR and ENDOR studies on a 5‐O‐membered crown ether bearing a triphenylmethyl moiety
Authors: Tajima Kunihiko , Shimizu Hiroaki , Morita Takaaki , Tomoda Hideyuki , Mukai Kazuo , Ishizu Kazuhiko
Published: May 2005

A new 5‐O‐membered crown ether spin‐labelled with a triphenylmethyl group was prepared. The intramolecular unpaired π‐electron delocalization was investigated by ENDOR. The ENDOR of the crown methylene group adjacent to the aromatic ring revealed non‐equivalence in the magnitude of the proton hyperfine splittings. Based on the temperature‐dependent ENDOR line separation, the activation energy of the conformational change of the methylene protons was estimated. Upon metal chelation into the crown ring the dissociation of the dimer to the monomer radical was greatly affected, and an increase in the activation energy of the vibrating methylene protons was detected.
13C NMR spectra and structure of mono‐, di‐ and trimethoxyphenylethylamines and amphetamines
Authors: Bailey Keith , Legault Donald
Published: May 2005

Carbon‐13 and proton chemical shifts of mono‐, di‐ and trimethoxylated phenylethylamines (PEAs) and their hydrochlorides were determined and the signals were assigned and are reported. The data are interpreted to indicate that the side‐chains of PEA derivatives and amphetamine salts have the amino and aromatic moieties predominantlytrans(antiperiplanar), that ‘sandwiched’ OCH3groups and side‐chains are forced out of the ring plane and that planarortho‐OCH3groups have their electron lone pairs oriented toward the side‐chain and partially stabilizegaucherotamers. It is suggested that the location and density of electronic charges just outside the aromatic ring will significantly affect interactions with putative receptors.
Phosphol‐3‐ene 1‐oxides and ‐sulfides. A systematic investigation via carbon‐13 nuclear magnetic resonance spectroscopy
Authors: Buchanan G. W. , Webb V. L.
Published: May 2005

13C NMR chemical shifts and 13C31P couplings are reported for 18 phosphol‐3‐ene 1‐oxides and 18 corresponding sulfides. The effects of methyl substitution at positions 3 and 4 on the carbon shifts have been systematically explored and substituent parameters derived. One bond couplings from phosphorus to C‐2 and C‐5 have been related to the sum of the exocyclic substituent group electronegativities (covalent boundary potential values).
Nuclear magnetic resonance of phosphorus compounds: 9—The NMR spectra of phosphirane
Authors: Goldwhite Harold , Rowsell David , Vertal Lawrence E. , Bowers Michael T. , Cooper M. Ashley , Manatt Stanley L.
Published: May 2005

The 100 MHz proton and 40.4 MHz 31P NMR spectra of phosphirane (1) have been recorded at −20 °C and analysed iteratively to yield coupling constants and chemical shifts. The 22.6 MHz 13C spectrum of 1 was recorded at 0 °C and analyzed. The 31P chemical shift of 1 was measured as 40 467 515.97 ± 0.08 Hz relative to TMS as 100 000 000.00 Hz. The geminal P‐C‐H couplings in 1 are opposite in sign and of different magnitudes (+16.14 and −2.64 Hz); the PH coupling (+158.34 Hz) is smaller than that in any other organic phosphine. These observations are discussed and correlated with the geometry of 1. The electronic structure of the strained ring of 1 is discussed in terms of a localized valence bond approach.
Selective INEPT, a new technique for the13C NMR assignment of methylene carbons with non‐equivalent protons, and its application to the analysis of the13C NMR spectrum of monensin
Authors: Furihata Kazuo , Seto Haruo , Ohuchi Muneki , Otake Noboru
Published: May 2005

A new method based on the combination of selective proton decoupling and INEPT is explained in detail. This technique, named selective INEPT (SEL‐INEPT), is a useful and sensitive method for the13C NMR assignment of methylene carbons with non‐equivalent protons. The13C NMR spectrum of monensin has been analysed by the application of this technique.
Stereochemistry of organic sulphur compounds: 12—Configurational assignment of 2‐methylsulphinyl‐1‐phenylethanol and some O‐derivatives
Authors: Brunet Ernesto , Gracía‐Ruano José L. , Hoyos Miguel A. , Rodríguez Jesús H. , Prados Pilar , Alcudia Felipe
Published: May 2005

The conformational analysis of the diastereomeric 2‐methylsulphinyl‐1‐phenylethanol and its O‐methyl and O‐acetyl derivatives has been performed by 1H NMR spectroscopy. The study of the influence of dilution and solvent polarity changes on the coupling constants has permitted the configurational assignment of each diastereoisomer. The role played by hydrogen bonding in the hydroxysulphoxides has also been studied by IR spectroscopy.
Anisochrony of isopropyl methyl groups in 1‐isopropyl‐substituted tetralins and indans
Authors: Pourahmady N. , Palaniswamy V. A. , Eisenbraun E. J.
Published: May 2005

1‐Isopropyl‐5‐methylindan, 1‐isopropyl‐7‐methylindan and 1‐isopropyl‐1,2,3,4‐tetrahydronaphthalene show a large anisochrony (magnctic non‐equivalence) of the isopropyl methyl signals at room temperature in their1H NMR spectra. A decrease in magnitude of this anisochrony is observed, in each case, in the temperature range 30‐150 °C. However, for 1‐isopropyl‐8‐methyltetralin, the magnitude of the non‐equivalence of the isopropyl methyl signals is unexpectedly small. These latter signals converge at 85 °C and then diverge in the opposite direction over the range 85‐150 °C. This alteration in anisochrony with temperature change for all cases is observed as a continuous downfield migration of one signal which, in turn, results from variations in conformation populations.
The mass spectra of 1‐arylanthra‐9,10‐quinones
Authors: Buckle D. R. , Waight E. S.
Published: May 2005

The mass spectra of 1‐phenylanthra‐9,10‐quinone and 20 substituted l‐phenylanthraquinones having alkyl methoxyl, nitro and halogen substituents in the o‐, m‐ and p‐positions of the phenyl ring have been measured. The spectra are discussed with particular reference to the loss from the molecular ion of a hydrogen atom and of the substituent.
Fluorinated tropylium ions in the mass spectra of some polyfluoroaromatic compounds
Authors: Bruce M. I. , Thomas Mair A.
Published: May 2005

The most prominent ion in the mass spectra of C6F5CH2X (X  H, Br, CH:CH2, COCl, and CH2C6F5) is C7F5H2+, formulated as the pentafluorotropylium cation. This ion is also found, in an amount comparable to the parent ion, in the spectrum of (C6F5)2CH2. The heptafluorotropylium cation is found similarly in the spectrum of C6F5CF3. The mass spectra of (C6F5)2CHBr and [(C6H5)2CH]2 exhibit an ion C13F10H+ as the base peak, which is probably a pentafluorophenylpentafluorotropylium cation.

The alcohol (C6F5)2CHOH shows loss of C6F5, followed by 2H, as a major breakdown pathway.

The mode of formation, and the subsequent fragmentation, of the major ions in these spectra, are discussed.
A study of rearrangement processes in the mass spectra of substituted diphenyl‐ethers
Authors: Ballantine J. A. , Pillinger C. T.
Published: May 2005

An investigation of the mass spectra of a number of substituted diphenyl ethers has shown that the major fragment ions are commonly due to cleavage of the molecule into the two benzene ‘half’ fragments although in many cases the molecular ion is the most abundant species observed.

Little evidence is seen of MCO or MCHO peaks in these molecules but a large number of different rearrangement processes have been observed which involve ortho‐substituents. These rearrangement ions, although in some cases not very abundant, can be diagnostic in the problem of locating substituents in the diphenyl ether nucleus.
Derivatives of cyclotetrazenoborane (tetrazoborol‐2‐ine)—VI.1 Mass spectra of B substituted cyclotetrazenoboranes
Authors: Brittain E. F. H. , Leach J. B. , Morris J. H.
Published: May 2005

The mass spectra of B substituted 2,5‐dimethyl cyclotetrazenoboranes have been studied. The compounds Me2N4BD, Me2N4BEt, Me2N4BVi, Me2N4BCl and Me2N4BBr give confirmatory evidence that loss of N2+H. from the system occurs by loss of H from the side chain and that the BR bond is very stable under electron impact conditions. Fragmentation proceeds in a similar fashion to that of the 2,5‐dimethyl substituted compounds with H bonded to the boron atom.
Chemistry of lichen constituents—VI: Mass spectra of usnic acid, lichexanthone and their derivatives
Authors: Letcher R. M.
Published: May 2005

The mass spectra of usnic acid, decarbousnic acid, usnetic acid and usnetol are reported and mechanistically interpreted. The mass spectra of lichexanthone and lichexanthone methyl ether were also examined, and the unusal features of the latter spectrum have been rationalized.
Electron‐impact studies of organometallic molecules—X. Some simple transition metal fluorocarbon complexes
Authors: Bruce M. I.
Published: May 2005

The mass spectra of several fluoroalkyl, fluoroalkenyl and fluoroacyl complexes of manganese, rhenium, iron and ruthenium carbonyls are described. After loss of carbonyl groups, fluoroalkyl compounds eliminate an olefin, with formation of metal halide species. A trifluorovinyl complex shows a novel elimination of a carbon atom to give an ion postulated to be a difluorocarbene‐metal fluoride; the occurrence of difluorocarbene‐metal ions in the spectra of some related complexes is also discussed. The spectra of the acyl complexes show little evidence of elimination of the acyl carbonyl group; the major process is fission of the CORf bond with loss of a fluoroalkyl radical and formation of the cationic metal carbonyl, e.g. π‐C5H5M(CO)3+ (M  Fe or Ru). The relevance of thermal or photochemical model reactions to processes occurring in the mass spectrometer is discussed.
The mass spectra of some methyl norbornyl chlorides
Authors: Bunton C. A. , Del Pesco T. W.
Published: May 2005

The mass spectra of exo‐2‐norbornyl chloride, 1‐ and 2‐methyl exo‐2‐norbornyl, exo‐camphenilyl, apoisobornyl, bornyl and isobornyl chloride, and camphene hydrochloride, α‐ and β‐fenchyl chloride and fenchene hydrochloride, and exo‐isofenchyl chloride and 2,5,5‐trimethyl exo‐2‐norbornylchloride, and camphene and α‐fenchene have been examined at 12 to 16 and 80° eV and at 30 to 49 and 80°, or higher temperatures. Wagner‐Meerwein rearrangements occur very readily in the ion source and compounds related by these rearrangements give very similar fragmentation patterns. Thermal decompositions are important with the tertiary chlorides especially at higher source temperatures. The rates of methanolysis of some of these chlorides were measured.
Massenspektrometrischer Zerfall und Umlagerung von α‐Trifluoracetaminocarbonium‐Ionen
Authors: Prox A. , Schmid J.
Published: May 2005

α‐Trifluoracetaminocarbonium‐Ionen treten als charakteristische Bruchstücke in den massenspektren von N‐Trifluoracetyl‐α‐aminosäuren und deren Derivaten auf. Sie zerfallen unter Eliminierung stabiler Neutralmolekeln, wobei in erster LInie die Struktur ihres Substituenten entscheidenden Einfluß ausübt. Im Zuge dieser Fragmentierungen kommt es bei einer Reihe von Ionen zu bemerkenswerten Strukturumlagerungen.
Massenspektrometrischer Zerfall und Umlagerung von α‐substituierten N‐Methyl‐benzylamiden
Authors: Prox A. , Schmid J.
Published: May 2005

Der massenspektrometrische Zerfall einiger α‐substituierter N‐Methylbenzylamide mit verschiedenen N‐Acylgruppen wird anhand der Ergebnisse aus hochauflösender Massenbestimmung, Berechnung der metastabilen Ionen Untersuchung spezifisch deuterierter Verbindungen diskutitert. Dabei wird die Strukturumlagerung der durch α‐Spaltung entstandenen N‐Methyl‐α‐acylaminocarboniu‐Ionen nachgewiesen. Sie ist von der Art der N‐Acylgruppe abhängig. In den Massenspektren von N‐Acetyl‐bzw. N‐p‐Cl‐Benzoyl‐methyl‐α‐phenyläthylamid wird die Wanderung der α‐Methylgruppen beobachtet.
Mass spectra of some alkyl isoxazoles
Authors: Ohashi Mamoru , Kamachi Hajime , Kakisawa Hiroshi , Tatematsu Akira , Yoshizumi Hideo , Kano Hideo , Nakata Hisao
Published: May 2005

The mass spectra of several compounds obtained during the process of Stork's isoxazole synthesis9 as well as the related isoxazoles have been investigated. The fragmentations of simple alkyl isoxazoles are nicely formulated via azirine intermediates. A striking difference between the spectra of isoxazoles and those of methylfurans as to the relative abundance of [M — l] peaks is noteworthy. The very low abundance of these peaks in the former reflects the unique character of isoxazole nucleus due to the preferential cleavage of NO linkage rather than a benzylic CH bond rupture. If an alkyl substituent is present at 4‐position in 3,5‐dimethylisoxazoles, strong peaks at m/e 110, 68 and 43 are common in their spectra. The analyses of metastable transitions and high resolution measurements have demonstrated that the formation of these ions can be interpreted by a mechanism involving the cleavage of NO linkage.
The ions [CH3S]+, [C2H5S]+ and [CH3O]+ formed by electron‐impact
Authors: Amos D. , Gillis R. G. , Occolowitz J. L. , Pisani J. F.
Published: May 2005

The mass spectra of deuterated species shows that both the isomeric ions [CH2SH]+ and [CH3S]+ are formed in the ratio 2:1 from CH3SH; the ions [CH3CHSH]+ and [CH3CH2S]+ in the ratio 0·8:1 from CH3CH2SH; and [CH2OH]+ and [CH3O]+ in the ratio 6·7:1 from methanol.

The heats of formation of [CH3S]+ and [C2H5S]+ are of the order of 222 and 203 Kcal.mole−1 respectively. The isomeric ions cannot be distinguished on thermodynamic grounds.
Organic ions in the gas phase—XXI: Synthesis and mass spectra of deuteriothiophenes
Authors: Meyerson Seymour , Fields E. K.
Published: May 2005

Mass‐spectral and n.m.r. analysis of thiophenes labeled by exchange with deuteriosulfuric acid establishes that exchange at the 2 and 5 positions is essentially complete before any deuterium is incorporated at positions 3 and 4. Thus, such exchange is a satisfactory procedure for position‐specific labeling. Mass spectra of the labeled thiophenes show that about 60% of the [CHS]+ ion yield is derived from molecular ions that have not undergone prior rearrangement. The remaining 40% arises by a path or paths in which the four hydrogen atoms lose position identity. Other decomposition paths contributing to the mass spectrum are characterized by more nearly complete scrambling of hydrogens.
Mass spectrometric studies of structural isomers—II: Mono‐and bicyclic C6H10 molecules
Authors: Winters Robert E. , Collins Jerome H.
Published: May 2005

The electron‐impact‐induced ionization and fragmentation of six C6H10 structural isomers have been studied in order to determine the effect of isomerism upon their mass spectrometric behavior. The 70 eV mass spectra, metastable transitions and appearance potentials of the principal ions are reported. Significant differences between the mass spectra of the six isomers were observed; however, metastable transition and appearance potential data indicate that the fragmentation path‐ways are the same for all the C6H10 molecules. Experimentally determined ionization potentials for the structural isomers are presented and compared to ionization potentials calculated by the bond orbital method. Utilizing fragmentation pathways deduced from general features in the mass spectra and from observed metastable transitions, we calculated heats of formation (ΔHf) for the observed principal ions and compared these values to ΔHf values for isomeric ions from other molecules.
Mass spectrometry of methyltetrazoles
Authors: Forkey D. M. , Carpenter W. R.
Published: May 2005

The mass spectra of tetrazole, all isomers of monomethyl‐ and dimethyltetrazole, several trifluoromethyl substituted tetrazoles, as well as deuterated analogs, were recorded. Loss of N2 was the important fragmentation of the molecular ions of tetrazole and 2‐methyl substituted tetrazoles; however, HN2 loss was more important for 1‐methyl substituted tetrazoles. The 1‐methyl‐tetrazoles showed molecular ion peaks while the 2‐methyltetrazoles exhibited an unprecedented [M + 1] peak with no molecular ion.
Field ionization mass spectrometry—I. Nucleosides
Authors: Brown Peter , Pettit George R. , Robins Roland K.
Published: May 2005

The field ionization mass spectra of a series of nucleosides are reported, and compared with spectra obtained by conventional electron‐impact ionization. The latter are complex, with structurally significant molecular ion and sugar cleavage peaks often of low intensity or completely absent. In contrast, the field ion spectra are extremely simple, with all except guanosine (highest mass peak [M — 18]) showing intense molecular ion peaks, and the characteristic sugar (S) and base (B + H) cleavage products as the only other important fragments.
Massenspektrometrie instabiler moleküle—III: Nachweis und untersuchungen zur stabilität chlorsubstituierter dehydrobenzole in der gasphase
Authors: Grützmacher Hans‐Friedrich , Hübner Jürgen
Published: May 2005

3,4‐, 3,5‐, 3,6‐, und 4,5‐Dichlordehydrobezol sowie 3,4,5,6‐Tetrachlordehydrobenzol wurden durch Hochvakuumpyrolyse aus den entsprechend substituierten 1,2‐Dijodbenzolen bzw. Phthalsäureanhydriden erzeugt und massenspektrometrisch nachgewiesen. Die Ionisationspotentiale wurden nach dem RPD‐Verfahren gemessen und die Bildungsenthal pien der substituierten Dehydrobenzole abgeschätzt.
De l'origine du pic [M — 1] dans le spectre de masse de la N,N‐diméthylbenzamide
Authors: Biellmann J. F. , Hirth C. G.
Published: May 2005

Le pic à [M — 1] dans le spectre de masse de al N,N‐diméthybenzamide provient de la prete d'un hydrogène du noyau aromatique et nonpas d'un des groupes méthyles. La preuve en est faite en comparant les spectres de al N‐trideutériométhyl N‐méthyl‐, N,N‐di(trideutério)méthyl‐ et N,N‐diméthyl 2,4,6‐trideutério bezamide. On décrit la préparation de ces produits.
Charge localization in molecule‐ions upon electron‐impact. Mass spectra of some substituted 1‐carbamoyl‐ and 1‐thiocarbamoyl‐2‐pyrazolines and related compounds
Authors: Tam S. W.
Published: May 2005

The mass spectra of some substituted 2‐pyrazolines and a pyrazolidine are discussed. With the exception of III which favours McLafferty rearrangements prior to fragmentation, I, IV and V fragment to give isocyanate or isothiocyanate radicals and ions with structures corresponding to their heterocyclic molecular compounds. These results which can be explained in the light of the concept of charge localization at preferential sites, are in good agreement with the ionization potential studies on substituted ureas and thioureas.5 Other compounds show simple straight‐forward fragmentations upon electron‐impact.
Evidence for anchimeric assistance in the expulsion of bromine from ring‐substituted β‐phenylethyl bromides: When is a simple cleavage a rearrangement?
Authors: Shapiro Robert H. , Jenkins Thomas F.
Published: May 2005

Using the principles of the quasi‐equilibrium theory, substituent effects, deuterium labeling and comparison of compound behavior, we provide strong evidence for aryl participation in the expalsion of Br· from the molecular ion of β‐phenylethyl bromide and eleven of its ringsubstitued derivatives. This reaction shows a kinetic behavior which is typical of rearrangements, its activation energy is lower than that of similar reactions where participation is partially or completely precluded and substitute effects are not only consistent with a particular process, but are also consistent with those predicted from solution chemistry.
Die McLafferty‐Umlagerung als Hauptabbaureaktion 1,1‐di‐, tri‐und tetra‐alkylsubstituierter Äthylenderivate
Authors: Kraft Manfred , Spiteller Gerhard
Published: May 2005

Im Gegensatz zu den Olefinen I und II unterliegen die an der Doppelbindung alkylsubstituierten Olefine II bis IX keiner der Bruchstückbildung vorausgehenden Isomerisierung unter Wasserstoffwanderung. Bei den Olefinen III bis VIII ist die McLafferty‐Umlagerung die nahezu einzige Abbaureaktion der Molekülionen. Aus den Isomeren III und IV bzw. V und VI entsteht das gleiche McLaffetty‐Abbauprodukt, so daß die Spektren praktisch identisch sind.

Es wird ein allgemeingültiges Schema für das Auftreten identischer Massenspektren isomerer Verbindungen angegeben.

Ein Olefin der Struktur IX, bei dem die McLaffetty‐Umlagerung nicht möglich ist, zeigt bei Electronenbeschuß vorzugsweise. Befindet sich ein weiterer Alkylsubstitutent in der Kette, so tritt als Konkurrenzreaktion zur McLaffety‐Umlagerung der Bindungsbruch an der Verzweigungsstelle ein.
Metastable transitions in the mass spectra of ketals and ketones. Competition between loss of small and large radicals
Authors: Cooks R. Graham , Yeo Adrian N. H. , Williams Dudley H.
Published: May 2005

An investigation of competing metastable transitions in the mass spectra of ethylene ketals RSRLC(OCH2)2 (where RL is a larger n‐alkyl group than RS) has established that in most cases RS is lost with a lower activation energy than RL. This technique has also been applied to ketones RSRLCO, to show again that RS is usually lost with the lower activation energy (thus supporting earlier data based on relative daughter ion abundances at the threshold). In the classes of compounds so far investigated, although [M+ − RS] ions are formed with lower activation energies than [M+ − RL] ions, the ion yield of [M+ − RS] ions is anomalously low from ions of high internal energy. Factors which may influence the [M+ − RS]/[M+ − RL] ratio of daughter ion intensities are examined. It is suggested that at the threshold [M+ − RS] and [M+ − RL] ions may be formed with rearrangement, or from an electronic state that cannot be effectively populated from molecular ions of high internal energies.
Decomposition of 1‐(2‐thienyl)alkylalkanones under electron‐impact
Authors: Foster Norman G. , Higgins Robert W.
Published: May 2005

The major fragmentation paths of the 1‐(2‐thienyl)alkylalkanones ionized by electron impact are delineated by means of isotopically labeled molecules, metastable ion peaks and low ionization voltage data. A prominent process is cleavage of the bond beta to the carbonyl group with the concurrent rearrangement of a hydrogen atom. Another important process is cleavage alpha to the carbonyl group to produce the thienoylium ion analogous to the benzoylium ion. As expected, the data show that increasing the chain length by two methylene groups increases the total ion current. The bulk of this increase is found in the increased ion current of the rearrangement ion with the remainder being associated with alkyl fragments and oxygenated ion species.
Electron‐impact induced oxygen migration in the mass spectra of β‐ketoalkylidenephosphoranes
Authors: Aplin R. T. , Hands A. R. , Mercer A. J. H.
Published: May 2005

The mass spectra of six β‐ketoalkylidenephosphoranes have been examined. The spectra all exhibit an electron‐impact induced migration of oxygen to phosphorus reminiscent of their thermal decomposition.
Charge separation and ion‐pair formation in cations subsequent to electron‐impact
Authors: Seibl J.
Published: May 2005

Investigation of metastable ion transitions shows, that spontaneous charge separations (loss of an electron from a cation) and ion‐pair formations (loss of negative ions from positive ones)are taking place in conventional mass spectrometry. Such processes may be important factors in formation of doubly charged ions.
Analysis of the chemical composition of solid petroleum hydrocarbons by electron attachment (EA) mass spectrography with negative ions
Authors: Kajdas Czesław , Tümmler Rudolf
Published: May 2005

The composition of solid saturated hydrocarbons from slack‐wax after reaction with urea has been investigated by electron‐attachment (EA) mass spectrography with negative ions. From the spectra of the samples the content of paraffin hydrocarbons, monocyclic, dicyclic and other polycyclic naphthenes was calculated. The presence of n‐paraffins up to C46, isoparaffins and cycloalkanes up to C52 has been confirmed. In the paraffin series the concentration of normal paraffin hydrocarbons containing one and two 13C atoms was determined. On the basis of the results obtained the constitution of the samples and the possible structures of the hydrocarbons were discussed. The results obtained have shown that the solid hydrocarbons which react with urea not only consist of one‐ or two‐ring systems, but also of systems with up to five and six rings.
Negative ion mass spectra of highly fluorinated compounds
Authors: Chait E. M. , Askew W. B. , Matthews C. B.
Published: May 2005

The negative ion mass spectra of highly fluorinated molecules with varying functionality are discussed. Attempts to obtain negative molecular ions where no positive molecular ion was observed met with little success. An interesting structural correlation for fluorinated ethers was developed based upon the observation of the abundant perfluoro alkoxide anions, CF3O− and CF3(CF2)2O−, in the negative ion mass spectrum.
The mass spectra of griseofulvin analogues. Characteristic fragmentation processes in the mass spectra of spiro‐cyclohexenones and spiro‐cyclohexanones containing the griseofulvin skeleton
Authors: Ballantine J. A. , Fenwick R. G.
Published: May 2005

The mass spectra of a number of griseofulvin analogues have been examined and the fragmentations, which are characteristic of the basic skeleton of the molecule, have been determined. In all of the different structural types examined, the ring cleavages which predominate are found tol occur by fission of one or more of the bonds attached to the spiro carbon atom.

The degree of unsaturation in the spiro‐cyclohexane ring system is found to controll the type of fragmentation which occurs and the type of ring system which is present can therefore be identified by its mass spectrum.
Etude de la fragmentation de derives de L'uracile et de la thymine par Spectrometrie de masse
Authors: Ulrich J. , Teoule R. , Massot R. , Cornu A.
Published: May 2005

Nous présentons und série de spectres de masse originaux, de dérivés de l'uracile et de la thymine, ainsi que les schémas de fragmentation correspondants.

L'étude d'une première série de molécules, à caractère aromatique, dont une marquée au 14C, a permis de confirmeer le mécanisme de base de la fragmentation comme étant un ‘retro Diels Alder’.

Une deuxième série, Saturée en positoin 5,6 du noyau, montre le caractère totalement différent de ces molécules, plus fragiles, plus sensibles à la nature des substituants et donnant un ion protoné [MH]+, responsable d'une partie des fragments observés.
The mass spectra of some α‐lactams
Authors: Lengyel István , Uliss David B. , Nafissi‐V M. Mehdi , Sheehan John C.
Published: May 2005

The electron‐impact induced fragmentation of eight aziridinones has been studied by conventional as well as by high resolution mass spectrometry. All α‐lactams exhibit a molecular ion. The major primary step, in the fragmentation, is the ejection of carbon monoxide from the molecular ion. Ions of the general formula R1NC and R2R3CO were found in the mass spectra of all α‐lactams investigated. A skeletal rearrangement to rationalize these ions is proposed. The fragmentation of the molecular ion is affected by the N‐substituent. Exact mass measurement and specific deuterium labeling indicate the absence of McLafferty rearrangement from either the N‐ or C‐substituent.
Zur Kenntnis des chinoiden Zustandes—XVI. Massenspektrometrische untersuchungen an chinonen, diphenochinonen und stilbenchinonen
Authors: Heiss J. , Zeller K.‐P. , Rieker A.
Published: May 2005

Außber den o‐Benzochinonen und o‐Naphthochinonen zeigen auch p‐Chinone, sowie Diphenochinone und Stilbenchinone [M + 2]+·‐Peaks. Diese beruhenim wesentlichen auf der Restfeuchtigkeit mi Massenspektrometer und hängen stärker vom Partialdruck dersubstanzen bzw. des Wassers als von der Temperatur ab. Die Spektren der [M + 2]+·‐Ionen entsprechen denjenigen der zugehörigen ionisierten Hydrochinone. Zwischen dem Redoxpotential und der Instensität des [M + 2]+·‐Peaks p‐chinoider Systeme besteht ein Zusammenhang. Die elektronenstoßinduzierte Fragmentierung von 2.6‐Di‐tert.‐butyl‐benzochinon‐(1.4) und 3.5‐Di‐tert.‐butylbenzochinon‐(1.2) wird diskutiert.
The electron‐impact induced loss of CHNO from 1,3‐bis‐(3‐m‐tolyl‐1,2,4‐oxadiazol‐5‐yl)hexafluoropropane
Authors: Cotter J. L. , Dickinson Hilary
Published: May 2005

High resolution mass measurement established that the m/e 425 peak in the mass spectrum of 1,3‐bis‐(3‐m‐tolyl‐1, 2,4‐oxadiazol‐5‐yl)hexafluoropropane corresponds to [M  CHNO]. This peak is absent from the mass spectrum of the para isomer.
Electron‐impact‐induced fragmentation of aromatic cyclic diazoketones
Authors: Dejongh D. C. , Van Fossen R. Y. , Dusold Laurence R. , Cava M. P.
Published: May 2005

The mass spectra of eleven diazoketones have been obtained. High resolution mass measurements of selected ions have shown initial loss of nitrogen followed by loss of carbon monoxide. In many of the spectra, flat‐topped metastables were observed.
Mass spectra of 2H‐1,4‐benzoxazine and‐benzothiazine hydroxamic acids
Authors: Coutts R. T. , Hindmarsh K. W.
Published: May 2005

The mass spectra of various benzoxazine and benzothiazine hydroxamic acids and related lactams have been recorded and interpreted. Proposed fragmentations have been substantiated by means of deuterium‐labeling and accurate mass measurements. Abundant molecular ions were observed in all spectra. The benzoxazine hydroxamic acids fragmented initially by expelling an oxygen atom and a COOH radical from the molecular ion. The corresponding benzothiazine hydroxamic acids lost an oxygen atom and an OH radical, whereas their 1,1‐dioxides decomposed by losing an oxygen atom and a ketene or substituted ketene molecule. The expulsion of CO, HCN, CS and SO2 molecules, as well as alkyl and NO radicals were common subsequent fragmentations.
Timing of hydrogen randomization in substituted diphenyl acetylenes
Authors: Safe S.
Published: May 2005

The mass spectra of halogenosubstituted diphenylacetylenes show hydrogen scrambling between the two phenyl rings. As with the halogenobenzenes the randomization process occurs i the molecular ion rather than in the [M – 1] ion as is the case for methyldiphenylacetylene (I, × = CH3).
Field‐ionization mass spectrometry—fragmentation and metastables
Authors: Chait E. M. , Kitson F. G.
Published: May 2005

Field‐ionization (FI) mass spectrometry is an established method for obtaining abundant molecular ions1 of a variety of compounds, and recently has been used in conjunction with exact mass measurements for determination of elemental compositions of molecules.2,3 Very little, however, has been reported on the value of normal fragment ions and metastable ions appearing in the FI spectrum as a source of structural information.
The high‐resolution mass spectra of aliphatic aldehydes
Authors: Harrison A. G.
Published: May 2005

The mass spectra of the C3 to C9 n‐alkanals and a number of branched aldehydes have been obtained at a resolution sufficient to resolve the OCH4 doublets. From the resolved spectra, a study of metastable transitions, and the spectrum of one deuterium‐labelled alkanal, (n‐hexanal‐2,2‐d2) the major fragmentation reactions have been elucidated. Of particular interest are the γ‐cleavage reaction, leading to [C3H5O]+ in the n‐alkanals, which proceeds both by a simple cleavage and by cleavage preceded by hydrogen interchange, and the loss of C2H4, which involves loss of the C2 and, probably C3, carbons.