bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low‐temperature 15N NMR spectra of reduced 1,3‐heterocyclic systems
Authors: Takeuchi Yoshito , Crabb Trevor A. 
Published: May 2005

AbstractThe 15N NMR spectra of the O‐inside cis‐fused conformer of perhydropyrido[1,2‐c][1,3]thiazine shows a shielding of the nitrogen of 23.0 ppm relative to the trans‐fused conformer. In contrast, 15N shifts for the cis‐and trans‐fused conformers of perhydro‐oxazolo[3,4‐a]pyridine and perhydrothiazolo[3,4‐a]pyridine show corresponding shieldings of only 0.6 and 2.5 ppm, respectively.
Heterocycles: 2—Regiospecific addition of methylhydrazine to acetylenic ketones
Authors: El‐Rayyes N. R. , Hovakeemian G. H. , Hammoud H. 
Published: May 2005

AbstractThe reaction of 1‐p‐methoxyphenyl‐3‐phenyl‐2‐propen‐1‐one and 3‐p‐methoxyphenyl‐1‐phenyl‐2‐propen‐1‐one with methylhydrazine gave 1‐methyl‐3‐p‐methoxyphenyl‐5‐phenylpyrazoline and 1‐methyl‐3‐phenyl‐5‐p‐methoxyphenylpyrazoline, respectively. These compounds, on oxidation, gave 1‐methyl‐3‐p‐methoxyphenyl‐5‐phenylpyrazole(2) and 1‐methyl‐3‐phenyl‐5‐p‐methoxyphenylpyrazole, respectively. When methyl‐hydrazine was made to react with 1‐p‐methoxyphenyl‐3‐phenyl‐2‐propyn‐1‐one, a pyrazole was obtained which proved to be identical with 2. Confirmatory evidence for this identity was obtained from their spectral data.
13C, 1H and 31P dynamic NMR studies of tetraalkyldiphosphanes: Barrier to internal rotation about the PP Bond in tetraisopropyldiphosphane
Authors: Albrand J. P. , Cogne A. , Taieb C. 
Published: May 2005

AbstractThe 1H, 31P and 13C NMR spectra of tetramethyldiphosphane (1), tetraethyldiphosphane (2) and tetraisopropyldiphosphane (3) have been studied in the temperature range 30 to −150°C and at magnetic induction up to 5.87 T. In the range −100 to −135 °C, the 1H and 13C spectra of 3 show important changes which can be attributed to freezing the interconversion between two equivalent non‐trans conformations. The line shape analysis of the 13C signals leads to ΔG≠ = 29.4 kJ mol−1 at −113 °C for the dynamic process involved. The spin coupling parameters 1J(PP) and N(PC) = 1J(PC) + 2J(PC) observed for 1 in the temperature range 30 to −120 °C show variations which could be due to a preference for the trans conformation in this diphosphane.
13C NMR study of isoxazolines and isoxazolidines in the thiophene and benzo[b]thiophene S‐oxide and S,S‐dioxide series
Authors: Durand Robert , Geneste Patrick , Olivé Jean‐Louis 
Published: May 2005

AbstractThe 13C NMR spectra were recorded for isoxazolines and isoxazolidines from 2,4,6‐trimethylbenzonitrile oxide or α‐phenyl‐N‐phenyl nitrone as dipolarophiles with the thiophene and benzo[b]thiophene S‐oxide and S,S‐dioxide series. The effects of the isoxazoline or isoxazolidine groups are not very different. Owing to the electronegativity of the oxygen atom, the main influence arises from the regioselectivity of the addition to the carbon atoms located at the α or β position from SO or SO2.
Analysis of 1H NMR spectra of fluorene and azafluorenes: Long‐range coupling constants
Authors: Fomichov A. A. , Lawani‐Edogiawerie S. O. , Prostakov N. S. 
Published: May 2005

AbstractAnalyses of the 1H NMR spectra of fluorene, 2‐nitrofluorene, 1‐azafluorene, 2‐azafluorene, 4‐azafluorene, 7‐nitro‐4‐azafluorene and 1,4‐diazafuorene have been carried out using computer calculations and homo double resonance techniques. The relative signs and magnitude of the 4J, 5J and 6J long‐range coupling constants of the 9‐CH2 group protons with the pyridine and phenylene ring protons have been measured by five‐ and six‐spin calculations. It was established that the presence of substituents and the N heteroatom has only a very weak effect on the values and signs of these coupling constants. The usual alternating signs of long‐range coupling constants involving π‐electron systems were confirmed, giving negative signs for even and positive signs for odd numbers of bonds separating the coupling protons.
Carbon‐13 NMR spectra of 1,4‐benzodiazepines—influence of the 7‐substituent
Authors: Paul H.‐H. , Sapper H. , Lohmann W. , Kalinowski H. O. 
Published: May 2005

AbstractCarbon‐13 NMR spectra of 1,4‐benzodiazepines, substituted differently at C‐7, are reported. With increasing electron demand of the substituent the signal of C‐2 is shifted upfield, an effect which is interpreted in terms of a π‐polarization of the carbonyl π‐electrons. This mechanism also seems to be of importance for the π‐electrons of the 5‐phenyl substituent and of the (N‐4)(C‐5) bond. Owing to the formation of hydrogen‐bonded self‐associates, compounds with a free amide group show concentration‐dependent shifts of some resonances. This is most obvious for C‐2, the proposed proton accepting site for hydrogen‐bonded cyclic dimers.
Effect of allylic strain on the conformations of diphenyl‐substituted tetrahydro‐1,3‐oxazin‐2‐ones and hexahydropyrimidin‐2‐ones
Authors: Kurtev Bogdan J. , Lyapova Maria J. , Mishev Stoyan M. , Nakova Olga G. , Orahovatz Alexander S. , Pojarlieff Ivan G. 
Published: May 2005

AbstractThe conformations of the cis and trans isomers of 4,6‐diphenyl‐, 4,5‐diphenyl‐ and 5,6‐diphenyltetrahydro‐1,3‐oxazin‐2‐one and 4,5‐diphenylhexahydropyrimidin‐2‐one, and of some of their N‐substituted derivatives, have been studied by 1H NMR. Conformers with 4a, 6e‐, 4a, 5e‐ and 5a, 6e‐phenyl groups are preferred in the respective isomers of the N‐H oxazinones, confirming a half‐chair conformation of the ring. Allylic strain caused by N‐substituents shifts strongly the a,e⇌e, a equilibria in trans‐4,6‐diphenyl‐ and cis‐4,5‐diphenyl‐oxazinones, but only moderately the e,e⇌a,a equilibria in the compounds with trans‐vicinal phenyl groups. In the latter, the diaxial conformation is preferred only in the case of bulky N‐substituents. The diaxial conformation is more favoured in the trans‐4,5‐diphenylpyrimidones.
Application of the computer program GENOA and two‐dimensional NMR spectroscopy to structure elucidation
Authors: Lindley Matthew R. , Shoolery J. N. , Smith Dennis H. , Djerassi Carl 
Published: May 2005

AbstractThe effectiveness and utility of the combined use of the interactive computer program GENOA and two‐dimensional double quantum coherence 13C NMR spectroscopy to solve structure elucidation problems are demonstrated with three examples. The substructural information inferred from the 1H NMR and 13C NMR spectra was insufficient to identify the structures of the example compounds. However, with the additional substructural information available from the two‐dimensional NMR experiment (which identifies directly bonded carbon atoms), the problems were solved in an extremely efficient manner.
The shielding of H‐α in the stabilized rotameric forms of α,α‐di‐tert‐butylthioacetic esters. The electric and magnetic anisotropic effects of the thione group
Authors: Balasubrahmanyam S. N. , Bharathi S. Narasimha , Usha G. 
Published: May 2005

AbstractThe currently accepted geometry of carbonyl magnetic anisotropic effects, if regarded as extendable to the thione group, imply that the more deshielded of the two H‐α lines in the1H NMR spectra of α,α‐di‐tert‐butylthioacetic esters should be assigned to the ‘180° form’ in which CS is antiperiplanar to C‐αH. CNDO results, however, indicate the opposite; the line should be assigned to the ‘O° form,’ in which CS eclipses C‐αH, if the predicted considerable increase in 1s density at H‐α on going from the 0° form to the 180° form is taken into account. A change in 1s density at H‐α as a result of increased branching of alkylation at C‐α is also found. These specific effects must be taken into account when discussing the anisotropic effects of CO or CS on H‐α shifts.
The NMR spectra of porphyrins: 22—Ring current effects in chlorins versus porphyrins
Authors: Smith Kevin M. , Goff Dane A. , Abraham Raymond J. , Plant James E. 
Published: May 2005

AbstractThe proton NMR spectra of tetraphenylporphyrin, octaethylporphyrin and the analogous chlorins (7,8‐dihydroporphyrins) are presented, and the chemical shift changes on chlorin formation are interpreted using a ring current model. In these compounds a general 10% reduction in the ring current occurs upon chlorin formation. Similar comparison of the chemical shifts of the corresponding dications and also of the protonated form of 2‐vinylphylloerythrin methyl ester with the corresponding chlorin, methyl pyropheophorbide‐a, shows that chlorin formation now has a much larger effect on the ring current, this reflecting the increased steric effects within the macrocycle which occur upon protonation. Variable temperature studies on the porphyrins and chlorins examined show clearly the effect of NH exchange processes and, in particular, novel intermolecular exchange processes with trifluoroacetic acid in the protonated species are recorded.
Configuration and NMR study of tricyclic oxazines fused to a norbornene or norbornane skeleton
Authors: Sohár P. , Stájer G. , Bernáth G. 
Published: May 2005

AbstractTricyclic oxazines fused with norbornane or norbornane were synthesized for pharmacological and stereochemical purposes. Analogous oxazin‐2‐ones and ‐2‐thiones were also obtained. The diendo or diexo anellation of the hetero ring to the norbornene or norbornane skeleton was confirmed by 1H and 13C spectral data. The assignment of the proton signals was proved and the proton‐proton coupling values were determined by double resonance experiments. With mono‐ and dichloroacetyl chloride, the oxazines fused to norbornene gave azetidinones which are mixtures of two isomers. The mixtures were separated into homogeneous substances, the configuration and conformation of which were determined via differential NOE experiments.
Carbon‐13 nuclear magnetic resonance examination of benzonorbornene derivatives. Assignment of site of aromatic ring substitution in benzonorbornen‐2‐ones
Authors: Reitz Thomas J. , Grunewald Gary L. 
Published: May 2005

Abstract13C nuclear magnetic resonance spectra were collected for a series of 5‐ and 6‐monoaromatic ring‐substituted benzonorbornadienes and 5‐, 6‐, 7‐, and 8‐monosubstituted benzonorbornen‐2‐ones. 13C chemical shifts values were found to be useful in the differentiation of the four monosubstituted aromatic ring isomers of benzonorbornen‐2‐one (1). We found that the 13C NMR spectrum of a substituted benzonorbornen‐2‐one (A) could be predicted with good accuracy (R2 for each aromatic carbon ≥ 0.925) from a knowledge of the 13C NMR spectrum of 1 and the appropriately substituted benzene. The substituents studied were NO2, NH2, I, CF3, CN, OCH3, and H. Correlation analysis showed that the carbonyl in A was effectively insulated from the ring π‐system.
1H and 13C NMR spectra of cyclic trimers, tetramers and pentamers derived from p‐substituted phenylacetylenes
Authors: Rao V. V. Ramana , Griesbaum K. 
Published: May 2005

AbstractThe 1H and 13C spectra of p‐substituted 1,3,5‐triarylbenzenes, 7‐ and p‐substituted 1,3,9‐triaryl‐9‐methyl‐fluorenes and 2‐, 10‐ and p‐substituted 6,12,13a‐triaryl‐12‐methylbenzo(6,7)cycloheptadieno[1,2,3‐jk]fluorenes have been examined. p‐Substituents were methoxy, methyl and fluorine groups. The 1H spectra were recorded at 300 MHz and permitted assignments for the aromatic protons by selective proton decouplings. Partial assignment of the carbon atoms in the 13C spectra was also possible.
The NMR spectra of the porphyrins: 23—Metalloporphyrins as diamagnetic shift reagents, chemical applications
Authors: Abraham Raymond J. , Bedford Geoffrey R. , Wright Brian 
Published: May 2005

AbstractSome applications illustrating the use of zinc (II) meso‐tetraphenylporphyrin (ZnTPP) as a diamagnetic shift reagent are described. The complexation shifts (ΔP) in a series of substituted pyridines are shown to be determined by both the basicity of the coordinating nitrogen atom and steric effects of ortho‐substituents. The selectivity of ZnTPP (N»O) in the simplification of the spectra of multifunctional ligands is demonstrated. Addition of the reagent neither affects the rotamer populations of the Inderal side‐chain nor produces any distortion of the 2‐benzylmorpholine ring. In addition, the substrate‐reagent solution may be shaken with D2O to identify exchangeable protons. The application of ZnTPP in structural problems involving substituted imidazo[2,1‐b]thiazoles and 2‐benzyl‐1,3‐dioxopyrrolo[3,4‐c]pyridines allows unambiguous identification of the possible structural isomers. To overcome the solvent limitations of ZnTPP, the more soluble Co(III)TPPBr can be used successfully as a shift reagent in DMSO‐d6, CD3OD and acetone‐d6 solutions.
Structural studies on 9‐hydrazono‐6,7,8,9‐tetrahydro‐4‐oxo‐4H‐pyrido[1,2‐a]pyrimidines by 1H, 13C and 15N NMR spectroscopy
Authors: Tóth Gábor , Szöllösy ÁRon , Almásy Attila , Podányi Benjámin , Hermecz István , Breining Tibor , Mészáros Zoltán 
Published: May 2005

Abstract1H, 13C and 15N NMR studies demonstrated that 9‐hydrazono‐6,7,8,9‐tetrahydro‐4‐oxo‐4H‐pyrido‐[1,2‐a] pyrimidlnes exist as an equilibrium mixture of Z‐E isomers in the hydrazono–imino tautomeric form having an exocyclic double bond. Proton‐catalysed Z‐E interconversion is fast. Substituent and solvent effects revealed that the decisive factors controlling the Z:E ratio are internal hydrogen bonding in the Z‐isomer, stabilization by solvation and steric interaction.
Electronegativity and linear electric field effect on γ‐anti13C chemical shifts
Authors: Duddeck Helmut , Islam Md. Rabiul 
Published: May 2005

AbstractThe contribution from the existence of a 1,3‐diaxial H‐α ⃛H‐γ arrangement to the γ‐anti effects of substituents X, which was previously believed to be generally shielding, is shown to be extremely dependent on the electronegativity of substituent X. In the presence of axial γ‐substituents Y, linear electric field effects appear to play a significant role if the C‐γ—Y bond is highly polarizable.
Carbon‐13 NMR spectra of chlorophyll a, chlorophyll a′, pyrochlorophyll a and the corresponding pheophytins
Authors: Lötjönen Simo , Hynninen Paavo H. 
Published: May 2005

AbstractThe 13C NMR spectra of C‐10 epimeric chlorophylls a and a′, pheophytins a and a′, pyrochlorophyll a and pyropheophytin a have been recorded and assigned by chemical shift comparison, by long‐range selective 1H decoupling experiments and by the examination of the fully coupled spectra. Various factors influencing the 13C chemical shifts of the chlorophyll derivatives, e.g. the coordination of magnesium to the chlorin nucleus, the effect of solvent and the steric strain at the periphery of the macrocycle, have been examined. The 13C NMR spectra of chlorophyll a measured in acetone‐d6 and tetrahydrofuran‐d8 (THF) were compared, and remarkable solvent effects on the 13C chemical shifts were observed. These effects were interpreted mostly in terms of specific chlorophyll‐solvent interactions. Different electron donor and steric properties of acetone and THF were considered to cause conformational alterations in the macrocycle, induced by the ligation of the solvent molecule(s) to the axial position(s) of the central magnesium atom of chlorophyll a. These results show that 13C NMR spectroscopy is a method of high information value for investigations of the unique electron donor acceptor (EDA) properties of the chlorophylls. The structural differences between the C‐10 epimeric chlorophylls and pheophytins were examined in terms of the substituent chemical shift (SCS) parameters for the C‐10 methoxycarbonyl group. The analysis showed that the change from the (10R) to the 10(S) configuration induces conformational alterations in the whole macrocycle which are, however, most prominent in rings IV and V. Owing to the increased steric interaction (repulsion) between the bulky substituents at C‐7 and C‐10, the peripheral strain is larger in the (10S) form, and is relieved by more pronounced deviations of rings IV and V from the macrocyclic plane compared with the (10R) form. The examination of the SCS parameters also showed that the peripheral steric strain is dissipated to a larger extent over the entire macrocycle in the Mg‐free derivatives. These results confirm the previous conclusions based on 1H NMR and CD data. The possible function of chlorophyll a′ in photosynthesis is briefly discussed.
Direct structure determination of the self‐condensation product of 1‐phenylpentane‐2,4‐dione using T1 and NOE measurements from 13C NMR spectroscopy
Authors: León V. , Espidel J. , Bolívar R. A. 
Published: May 2005

AbstractThe nuclear Overhauser effect (NOE) is known to depend on molecular dynamics and structure. However, in some cases the values obtained for selective homonuclear and heteronuclear NOE are much too small, considering that the nuclei involved are located within a short distance of each other in space. A quantitative treatment of the NOE values allows a clear explanation of this apparent anomaly, and allows the possibility of using T1 and NOE values measured with broad‐band proton irradiation. The corresponding relationship is useful for solving many structural problems in organic chemistry, and has the great advantage of employing the typical high resolution of fully decoupled spectra. The method was used in this work for the structure determination of the self‐condensation product of 1‐phenylpentane‐2,4‐dione, and it was concluded that the previous assignment of the 13C NMR spectrum was erroneous. An independent proof of the new assignment is given using the selective collapse of the fine structure under low‐power irradiation of the methyl protons.
The mass spectra of some alkyl and aryl oxazoles
Authors: Bowie J. H. , Donaghue P. F. , Rodda H. J. , Cooks R. Graham , Williams Dudley H. 
Published: May 2005

AbstractThe mass spectra of a variety of alkyl and aryl oxazoles have been determined and the spectra analyzed with the aid of deuterium labelling and high resolution mass spectrometry. In contrast to the corresponding benzenoid compounds, the mass spectra of isomeric alkyl oxazoles are distinctive and in this respect are akin to those of the corresponding pyridines. Further analogy to the pyridines is suggested by the unfavorable nature of a carbonium ion adjacent to the 2‐position and this effect may be used to locate alkyl substituents attached to the oxazole nucleus. The loss of carbon monoxide from the molecular ions of 2,5‐disubstituted oxazoles probably occurs with ring opening and migration of the C‐5 substituent (e.g.Br) to the C‐4 position.
A study of rearrangement processes in the mass spectra of substituted benzophenones which provide a guide to orientation
Authors: Ballantine J. A. , Pillinger C. T. 
Published: May 2005

AbstractAn investigation of the mass spectra of substituted benzophenones has shown that a number of rearrangement processes are operative. The rearrangements have been shown to involve solely theortho‐substituents to the carbonyl group and in many cases the carbonyl oxygen atom itself participates in the processes. Deuterium labelling experiments combined with data obtained from accurate mass and metastable analysis have enabled the probable mechanisms of rearrangement and fragmentation to be elucidated. An understanding of these processes should greatly assist in the location of substituents in unknown benzophenones.
The symmetry of the Ion formed by stepwise loss of CO molecules in the mass spectra of p‐benzoquinones
Authors: Elwood Thomas A. , Bursey Maurice M. 
Published: May 2005

AbstractContrary to previous suppositions, it appears that the produced by the loss of 2 CO from para‐benzoquinones passes through the symmetry of not a substituted cyclobutadiene, but rather a substituted tetrahedrane, at least for inert R. The p‐fluoro labeling technique is used to obtain this result.
Mass spectrometry of aralkyl compounds with a functional group—VII. On the structure of the ions C8H9+ from C6H5C2H4X‐ and C9H11+ from C6H5C3H6X‐compounds
Authors: Nibbering N. M. M. , De Boer Th. J. 
Published: May 2005

AbstractThe C8H9+‐ion, formed from the molecular ions of 2‐phenyl‐1‐bromoethane, 1‐phenyl‐1‐bromoethane and of 1‐phenyl‐1‐nitroethane by loss of the bromine atom and of the nitro group, splits off a molecule of acetylene after an almost complete randomization of hydrogens, as proved by deuteration. An eight‐membered ring structure for the C8H9+‐ion is proposed to explain these results.By loss of the nitro group from the molecular ions of 1‐phenyl‐1‐nitropropane and of 1‐phenyl‐2‐nitropropane the well‐known phenylated cyclopropane ion3 (C9H11)+ is generated. Mass spectra of analogues, specifically deuterated in the side‐chain, show that in this ion a randomization of hydrogen atoms in the cyclopropane ring as well as a hydride transfer from the cyclopropane ring to the phenyl cation occur.
The mass spectra of some triterpenoid dehydration products
Authors: Elgamal M. H. A. , Fayez M. B. E. , Kemp T. R. 
Published: May 2005

AbstractThe mass spectra of ten dehydration and solvolysis products obtained from β‐amyrin and glycyrrhetic acid were studied. With the exception of those resulting from ‘backbone’ rearrangement, they exhibited conventional fragmentation due to the ring C chromophore, like the parent alcohols. Only those products with a contracted ring A suffered loss of an isopropyl radical. In the latter type, special fragmentation features were exhibited by the isopropylcyclopentene and by the isopropylidene products. These differences enabled the assignment of probable structures for two unknown derivatives.
Mass spectometry in structural and stereochemical problems—CLXVIII. Effect of fluorine substitution on the McLafferty rearrangement of aliphatic ketones.
Authors: Carpenter Wayne , Duffield A. M. , Djerassi Carl 
Published: May 2005

AbstractThe mass spectra of allphatic ketones are drastically altered following substitution of a trifluoromethyl entity adjacent to the carbonyl group (II and III) or attachment to the γ‐carbon atom (V). Loss of the trifluoromethyl group by α‐cleavage far exceeds the alternative elimination of an alkyl radical. Virtually complete repression of the McLafferty rearrangement process (I → a) occurs when a CF3 group is attached to the γ‐carbon atom. A fluorine atom is not transferred in lieu of hydrogen in the McLafferty rearrangement as demonstrated by the mass spectrum of 1,1,1,7,7,7‐hexafluoroheptan‐4‐one (IV). Rationalization for these results are presented as is a description of the syntheses of several hitherto unknown fluorinated ketones.
Mass spectra of organometallic compounds—VIII. Some transition metal organometallic halide derivatives
Authors: King R. B. 
Published: May 2005

AbstractThe positive ion mass spectra of the transition metal organometallic halide derivatives C5H5M(CO)3Cl(M  Mo or W), C7H7W(CO)2I, C3H5Fe(CO)3I, [C3H5PdCl]2, and [C5H5Mo(NO)I2]2have been investigated. Further examples of the elimination of CO and C2H2fragments were noted. In addition the following effects of particular interest were observed:(i) Evidence in the mass spectra of the chlorides for reactions with adventitious iodine and even bromine present in the mass spectrometer; (ii) Evidence for conversion of the compounds C5H5Mo(CO)3X to the new halides [C5H5Mo(CO)X]2upon pyrolysis; (iii) Evidence for facile losses of the π‐allyl group, the iodine atom, and methyl iodide in the mass spectrum of the π‐allyl derivative C3H5Fe(CO)3I; (iv) Evidence for loss of iodine upon introducing [C5H5Mo(NO)I2]2into the mass spectrometer to give ions derived from [C5H5Mo(NO)I]2.
Mass spectra of some acyclic α,β‐unsaturated aldehydes, ketones and esters
Authors: Bowles A. J. , Brittain E. F. H. , George W. O. 
Published: May 2005

AbstractThe mass spectra of a series of aliphatic acyclic α,β‐unsturated aldehydes, ketones and ester have been examined. The spectra do not show evidence for McLafferty rearrangements, alkoxyl migration or for fragmentations which are dependent upon the s‐trans or s‐cis conformations of the compounds. There is some evidence for cis‐trans isomerism about the double bond.