bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ring‐opening reactions. 6. eliminative ring fission of aziridinium and azetidinium ions
Authors: Gionta Grazia , Lillocci Claudio 
Published: January 2005

AbstractThe reactivity ratio between the three‐ and four‐membered cyclic ammonium ions in ring‐opening elimination reactions was measured. The comparison with the analogous ratio obtained in a previous study on ring‐opening substitution reactions suggests a substantial difference in the effect of the stereochemical factors governing the two ring‐opening reactions and confirms the anomalous behaviour of small rings in the ring‐opening substitution reaction.
3‐Methylcarboxy‐1H‐indazole. Theoretical study of its formation via intramolecular aliphatic diazonium coupling and x‐ray crystal structure
Authors: Glaser Rainer , Mummert Caryn L. , Horan Christopher J. , Barnes Charles L. 
Published: January 2005

AbstractThe methyl ester of 1H‐indazole‐3‐carboxylic acid (2‐Me) is formed in the diazotization of o‐aminophenylacetic acid to o‐diazoniumphenylacetic acid (1) in an intramolecular aliphatic diazonium coupling. 2‐Me was identified and characterized by single‐crystal x‐ray diffraction and found to crystallize as hydrogen‐bonded trimers of crystallographically independent molecules. The methylcarboxy groups are rotated slightly out of the best plane of the trimer resulting in only a pseudo‐threefold axis. The crystal structure of 2‐Me is compared with other indazoles and pyrazole. Regioselective electrophilic diazonium ion addition to the enol tautomer of 1 and subsequent hyrazone–azo tautomerization are proposed as a possible mechanism for indazole formation under acidic conditions. The tautomerization equilibrium between acetic acid and its enol 1,2‐dihydroxyethene was studied and the effects of phenyl and o‐diazoniumphenyl substitution on this equilibrium were explored with semi‐empirical quantum mechanical methods. The performance of the semi‐empirical method was assessed by comparison with ab initio and/or experimental data. It was found that the enol of o‐diazoniumphenylacetic acid is stabilized greatly owing to extended conjugation and push–pull interactions in the enol form. These results suggest that the enol tautomer might be a viable reactive intermediate that warrants considerations in discussions of reaction mechanisms.
Radical reactions of epoxides. 2. intramolecular competition between cyclopropylmethyl and oxiranylmethyl radical ring‐opening rearrangements
Authors: Krosley Kevin W. , Gleicher Gerald Jay 
Published: January 2005

AbstractThe erythro‐thioimidazole precursor to the cyclopropyloxiranylmethyl radical has been prepared. Treatment with 7–19 equiv. of triphenyltin hydride at 70°C gave only 3‐cyclopropylprop‐2‐en‐1‐ol, the product of epoxide ring opening. No product in which the cyclopropyl ring had opened was observed. Kinetic analysis allowed the assignment of a lower limit for the rate of oxiranylcarbinyl radical rearrangements of 1 × 1010 s−1 at this temperature.
Photochemical and radiolytic cleavage of 10‐methylacridine dimer in solutions and cryogenic glasses
Authors: Adamus Jan , Rogowski Jacek , Michalak Jacek , Paneth Piotr , Gebicki Jerzy , Marcinek Andrzej , Platz Matthew S. 
Published: January 2005

Abstract10‐Methylacridine dimer [(AcrH)2] dissociates into a pair of 10‐methylacridyl radicals (AcrH˙) on laser excitation (308 nm) in solvents of various polarities. Exposure of (AcrH)2 in methylcyclohexane glass at 77 K to γ‐rays of 60Co generates the radical cation (AcrH). Thermal annealing of the matrix to 90 K results in dissociation of (AcrH) into AcrH˙ and 10‐methylacridinium cation (AcrH+).
Substituent effects in carbon‐13 NMR spectra of aminopyridines
Authors: Rasała Danuta 
Published: January 2005

Abstract13C NMR spectra of 45 vicinally substituted 2‐, 3‐ and 4‐aminopyridines were investigated. The substituent effects are evidently sensitive to the position of both the substituent and the fixed amino group. In the para position with respect to the substituent, long‐range electronic effects are expressed by the dual substituent parameter treatment (DSP), and the resonance contribution is more important than the inductive contribution. Correlation results for the ipso and ortho carbon atoms using the more sophisticated extended DSP equation suggest non‐electronic effects of unknown origin.
Stereochemistry of aminolysis of N‐pentafluorophenylcarbonimidoyl dichloride. Crystal and molecular structures of N2‐pentafluorophenyl‐N1,N1‐dibenzylchloroformamidine
Authors: Mikhailov V. A. , Yufit D. S. , Balabanov E. Yu. , Struchkov Yu. T. , Popov A. A. , Savelova V. A. , Kolesnikova I. V. , Petrova T. D. , Platonov V. E. 
Published: January 2005

AbstractIt has been established that the product of the reaction of N‐pentafluorophenylcarbonimidoyl dichloride (1) with dibenzylamine, viz. N2‐pentafluorophenyl‐N1,N1‐dibenzylchloroformamidine (4a) is a Z‐isomer, whereas according to the concept of stereoelectronic control one might have expected a product with E‐configuration. The heat of formation and the geometry of Z‐ and E isomer of N2‐pentafluorophenyl‐N1,N1‐diethylchloroformamidine (4b) (the latter is a product of the reaction of 1 with diethylamine) were calculated with the semi‐empirical MNDO method. The calculated geometry of (Z)‐4b was found to be in a good agreement with the experimentally determined structure of 4a. The formation of (Z)‐4b is more preferable energetically than that of (E)‐4b; the calculated difference in the heats of formation is 2·8 kcal mol−1. Thermodynamic control of the reaction stereochemistry is proposed.
Conformational analysis of substituted perhydro‐1,2‐oxazolo[3,2‐c] [1,4]oxazines by NMR spectroscopy
Authors: Wazeer Mohamed I. M. , Al‐Muallem Hasan A. , Ali Sk. Asrof 
Published: January 2005

AbstractThe 13C NMR spectra of most of the substituted perhydro‐1,2‐oxazolo[3,2‐c] [1,4]oxazines (3) at low temperature showed the presence of two isomers of unequal populations. The major isomer is shown to be the cis isomer {except in 2‐hydroxymethyl‐2‐methylperhydro‐1,2‐oxazolo[3,2‐c] [1,4] oxazine (3e)}, which is in equilibrium with the minor isomer (trans conformer) by a relatively slow nitrogen inversion. Intramolecular hydrogen bonding in oxazines, having 2‐hydroxymethyl substituents, is shown to be an important factor in determining the population ratio of the two isomers. The barrier to nitrogen inversion was determined by detailed band‐shape analysis of proton and carbon NMR spectra and were in the range 66·3–72·9 kJ mol−1. The chair inversion had been slowed down, in one case, trans‐dimethylperhydro‐1,2‐oxazol[3,2‐c] [1,4]oxazine‐2,3‐dicarboxylate (3j), to show the presence of the two forms of the cis isomers. The barrier to chair inversion is 41·5 kJ mol−1 as determined by proton NMR band‐shape analysis of 3j.
Intramolecular photoinduced electron transfer (PET) bond cleavage in some sulfonium salt derivatives. Effect of distance and thermodynamics on PET rate
Authors: Saeva Franklin D. , Martic Peter A. , Garcia Edwin 
Published: January 2005

AbstractThe rate of intramolecular photoinduced electron transfer (PET) between a naphthacene electron donor (D) and a sulfonium electron acceptor (A) was found to be dependent on the thermodynamics for PET and distance between D and A. The slopes of In kET vs through‐bond and through‐space distance plots was found to be −0·60 and −0·91 Å−1, respectively. The product distribution obtained from the photolysis of regioisomeric naphthacenyl sulfonium salt derivatives was found to be independent of distance. Photolysis of three regioisomeric naphthacenyl phenylmethyl‐p‐cyanobenzylsulfonium salts produced unsubstituted thiomethylphenylnaphthacene and mono‐, di‐ and tri‐p‐cyanobenzyl‐substituted thiomethylphenylnaphthacene. The appearance of the out‐of‐cage di‐ and trisubstituted photoproducts suggests that secondary photochemistry and intermolecular electron transfer bond‐cleavage reactions are occurring when the concentration of the sulfonium salt in acetonitrile is 10−2 and 10−3 M and the degree of conversion is high. The primary photoproduct is the mono‐substituted naphthacene derivative.
Simultaneous determination of primary and secondary thermodynamic isotope effects in tautomeric equilibria
Authors: Zhang Ben Li , Mabon Françoise , Martin Maryvonne L. 
Published: January 2005

AbstractNMR determination of site‐specific hydrogen isotope ratios at natural deuterium abundance (SNIF‐NMR) provides the basis for simultaneous access to primary and secondary thermodynamic fractionation factors in exchange reactions and avoids the need for selective isotope labelling of the reagents. The method was applied to the measurement of fractionation parameters involving OH, CH2, CH3 and =CH groups in keto–enol tautomeric equilibria. The fractionation factors relating the =CH and OH sites of the enol species are simply derived from 2H NMR spectra whereas the determination of isotope parameters which relate keto and enol positions exploits a combination of 2H and 1H NMR experiments. Since only monolabelled isotopomers have to be considered at natural abundance, the method also offers the advantage of avoiding the occurrence of complex equilibria associated with multi‐labelled species possibly introduced by deuterium enrichment. The primary equilibrium isotope effects illustrate a preference of deuterium for the methylene fragment of the keto form with respect to the ethylenic position of the enol tautomer. Since the enol species is itself engaged in a fast tautomeric equilibrium associated with a symmetric or unsymmetric double minimum potential, the thermodynamic parameters are averaged over the exchanging partners. It is shown that the average thermodynamic fractionation factor relating the OH and =CH hydrogens of the enol are significantly influenced by the nature of the substituents at both carbonyl positions of the β‐diketones. Moreover, methyl and chlorine substitution increases by a factor of about 1·1 the thermodynamic isotopic fractionation factor relating the –COCHCO– position of the keto form to the hydroxyl position of the enol.
Ion–molecule pairs as intermediates in solvolysis. Catalysis by the pyridine leaving group on the elimination reaction
Authors: Thibblin Alf , Sidhu Harvinder 
Published: January 2005

AbstractSolvolysis of the 1‐(1‐methyl‐1‐phenylethyl)pyridinium cation (1‐P+) in 25% (v/v) acetonitrile in water at 60°C provides the alcohol 2‐hydroxy‐2‐phenylpropane (1‐OH) as the main product along with the alkene 2‐phenylpropene (3). The formation of the elimination product 3 is promoted by the leaving pyridine. Thus, eight times more 3 is obtained from 1‐P+ than from the protonated ether 1‐OMeH+. Hydron abstraction by the leaving pyridine is only two times less efficient than with AcO− as leaving group. The results indicate that the ion–molecule pair 1+ –P has a significant lifetime. The elimination product is formed mainly from the ion–molecule pair. The free carbocation yields almost exclusively the substitution product.
Reactions of cycloalkyl chlorides and bromides with diphenylphosphide ions in liquid ammonia
Authors: Nazareno Mónica A. , Palacios Sara M. , Rossi Roberto A. 
Published: January 2005

AbstractThe reactions of cycloalkyl (butyl, pentyl, hexyl and heptyl) chlorides and bromides with diphenylphosphide ions were studied in liquid ammonia. Cyclobutyl chloride was unreactive, whereas the bromide reacted giving the substitution product cyclobutyldiphenylphosphine (isolated as the oxide) in good yields; this reaction was catalysed by light and partially inhibited by p‐dinitrobenzene (p‐DNB). Cyclopentyl, cyclohexyl and cycloheptyl chlorides did not react in the dark, but the substitution products were formed under irradiation, and these reactions were inhibited by p‐DNB. The bromides reacted in the dark or under irradiation, and these reactions were partially inhibited by p‐DNB. It can be then concluded that the reactivity of cycloalkyl halides depends on the ring size and the nucleofugal group. In addition, as the overall reactivity decreases, there is an increase in electron transfer reactions.
Structure, stabilization energies and chemical shifts of the cyclobutenyl cation. Does it have ‘aromatic’ homocyclopropenium ion character? An ab initio study
Authors: Sieber Stefan , Schleyer Paul v. R. , Otto André Henry , Gauss Jürgen , Reichel Felix , Cremer Dieter 
Published: January 2005

AbstractThe relatively high stability and the structure of the simplest homoaromatic carbocation, the cyclobutenyl cation 1, was established ab initio by using correlated wave functions at HF 6–31G*, MP2(full)/6–31G*, MP2(full)/6–311G** and MP4(SDQ,full)/6–31G* geometries. The stability of 1 was estimated using homodesmotic and isodesmic reactions. The heat of formation of 1 was estimated to be 244 kcal mol−1 (1 kcal = 4·184 kJ). Chemical shift calculations were carried out at correlated levels and are in good agreement with the experimental values. At all levels of theory chemical shift calculations confirm the bent structure of 1. The MP4(SDTQ,fc)/6–311G**//MP2(full)/6–311G** + ZPE(MP2/(full)6–31G*), QCISD(T,fc)/6–31 + G*//MP2(full)/6–31G* + ZPE(MP2(full)/6–31G*) and MP4(SDQ,full)/6–31G*//MP4(SDQ,full)/6–31G* + ZPE(MP2(full)/6–31G*) ring inversion energies of 9·1, 9·3 and 9·0 kcal mol−1, respectively, agree with experiment (8·4 ± 0·5 kcal mol−1). Triplet electronic states are not competitive energetically. The homoaromatic character of the cyclobutenyl cation is shown by the nearly equal charges on C‐1, C‐2 and C‐3, the considerable 1,3‐bond order, the short 1·74 Å C‐1C‐3 distance and the large stabilization energy relative to the allyl cation.
Multinuclear NMR study of a five‐membered ring ditellurium derivative
Authors: Stefaniak Lech , Kamienski Bohdan , Schilf Wojciech , Amosova Svetlana V. , Webb Graham A. 
Published: January 2005

Abstract125Te, 1H and 13C NMR data are presented for a five‐membered ring ditellurium derivative. The signals are assigned by means of integration and correlation spectroscopy. The NMR data are most consistent with the presence of one of the two possible structures.
Photochlorination of tetrachloroethene in carbon tetrachloride solutions
Authors: Miller J. S. , Ledakowicz S. 
Published: January 2005

AbstractValidation of the mechanism of tetrachloroethene photochlorination at low C2Cl4 concentrations was investigated. The reaction was examined in carbon tetrachloride solution. For initial tetrachloroethene concentrations below 2 mol I−1, the solvent participates in a free‐radical chain photochlorination. The presence of CCl4 disturbs the course of this particular chain reaction and influences the duration of the induction period.
Heats of formation of organic molecules by ab initio calculations: Alkyl radicals
Authors: Liu Ruifeng , Allinger Norman L. 
Published: January 2005

AbstractA bond and group equivalent scheme that allows the calculation of heats of formation for alkyl radicals from the ab initio restricted open‐shell Hartree–Fock 6–31G* energies was developed. For a group of 12 radicals, the rms error for the calculated heats of formation was 0·65 kcal mol−1 (1 kcal = 4·184 kJ). Heats of formation were predicted for the pentyl radical and six of its isomers for which the experimental values are unknown.
Solvent effects on initial and transition states in the reaction of m‐fluorophenyltriethyltin with mercuric chloride in methanol and methanol–water mixtures
Authors: Sedaghat‐Herati M. Reza , Enkvetchakul Bobby 
Published: January 2005

AbstractWe have investigated solvent effects on the aromatic electrophilic substitution reaction of m‐fluorophenyltriethyltin, 1, with mercuric chloride in order to obtain information about the polarity of the transition state. Second‐order rate constants have been determined for the reaction of 1 with mercuric chloride in methanol and methanol–water mixtures at 25·0°C, allowing determination of δΔG‡. Molar standard free energies of transfer (ΔG) for the same solvent mixtures have also been determined for 1 at 25·0°C. Combination of our δΔG‡ and δΔG values with literature data for ΔG of HgCl2 yield values of ΔG(TS), the standard free energy of transfer of the corresponding transition state (TS) in the reaction from methanol to aqueous methanol. It is shown that the reduction in activation energy accompanying replacement of methanol by water is due to initial state destabilization and not to TS stabilization. In fact, the TS is destabilized as methanol is replaced by water. Further analysis permits dissection of the free energies of transfer of the TS into electrostatic and non‐electrostatic components. Comparison of these electrostatic components for the 1/HgCl2 system with some model reactions shows that charge development in TS of 1/HgCl2 is approximately 0·5 units of electronic charge.
Studies on the thermal decarboxylation of 1‐alkoxycarbonylbenzotriazoles
Authors: Katritzky Alan R. , Zhang Gui‐Fen , Fan Wei‐Qiang , Wu Jing , Pernak Juliusz 
Published: January 2005

Abstract1‐Alkoxycarbonylbenzotriazoles on thermolysis lose carbon dioxide; the decarboxylation is accompanied by the formation of a mixture of 1‐ and 2‐alkylbenzotriazoles, with the N‐1 isomer predominating over the N‐2 isomer in all cases. A cross‐over experiment, in which heating equimolar amounts of 1‐benzyloxycarbonylbenzotriazole and 1‐(4‐methylbenzyloxycarbonyl)‐5,6‐dimethylbenzotriazole gave almost all the cross‐over products, supports the proposed intermolecular mechanism for this decarboxylation and the formation of 1‐ and 2‐alkylbenzotriazoles. No decarboxylation was observed for 1‐phenoxycarbonylbenzotriazole.
Use of the multifunctional autocorrelation method to estimate molar volumes of alkanes and oxygenated compounds. Comparison between components of autocorrelation vectors and topological indices
Authors: Zakarya Driss , Tiyal Fathallah , Chastrette Maurice 
Published: January 2005

AbstractThe Multifunctional Autocorrelation Method (MAM) derived from the autocorrelation method of Moreau et al. was used to calculate molar volumes for 300 linear or branched alkanes from C6 to C11 and 104 oxygenated compounds including 40 alcohols, 30 ethers and 34 ketones. Components Ci of a MAM connectivity vector were compared with several topological descriptors. MAM descriptors were generally more efficient than topological descriptors but good regressions were obtained for alkanes only when more than two components Ci were used. An excellent regression was obtained with four components (C0 to C4):

Models obtained using descriptors based on connectivity were good enough for many practical purposes. However, to derive models adapted to estimate molar volumes for alkanes, an autocorrelation vector V based on Van der Waals volumes (as given by Bondi) was considered. The best equation obtained again includes three components:

To extend the use of MAM to compounds containing heteroatoms, a set of alcohols, ketones and ethers, were each functional group represents a different interaction type, was considered. Chemical families were first studied individually, then the total set was considered. The components of an autocorrelation vector V based on Van der Waals volumes were used as molecular descriptors. Oxygenated compounds are correctly described by only one component V0. The correlation coefficient is 0·993 for all the chemical families studied, and the standard error of the estimate is low (s = 2·56). Comparison of standard errors of the estimate for Wiener's indices (s = 17·38) and autocorrelation components (s = 3·95), for all chemical families, shows that components of MAM are more efficient as molecular descriptors. The quality of regression equations was not significantly changed when 104 oxygenated compounds and 141 alkanes were studied in a global set.
Study of initial state and transition state solvation in the Menschutkin reaction of triethylamine with ethyl iodide in alcohols from infinite dilution activity coefficients
Authors: Gonçlalves Raquel M. C. , Calado António R. T. , Pinheiro Lídia M. V. , Albuquerque Lídia M. P. C. , Macedo Eugénia A. 
Published: January 2005

AbstractThe Gibbs energies of activation of the Menschutkin reactions of trethylamine with ethyl iodide in 10 monoalcohols and nine dialcohols, were dissected into contributions from the initial state and transition state. To perform this study, the infinite dilution activity coefficient values of the solutes in the solvents, γ∞, were determined by the UNIFAC group‐contribution method, using the modified Flory–Huggins equation in the combinatorial term. For triethylamine, the γ∞ values were calculated using group‐interaction parameters from the VLE Parameter Table, due to the nonavailability of specific γ∞ UNIFAC interaction parameters for the relevant groups. For ethyl iodide, the γ∞ values were calculated using the group‐interaction parameters from the specific γ∞ UNIFAC Parameter Table, except for the solvents diethylene glycol and triethlene glycol, where VLE parameters were used for the same reasons as explained above for the triethylamine. The results were compared with those obtained for the unimolecular decomposition of tert‐butyl halides. For the Menschutkin reaction, we conclude that solvent disruption and reorganization to a state appropriate to solvating the molecular species is a dominant interaction mechanisim.
A reinvestigation of the reactions between diazomethane and 1‐phenylurazole
Authors: Bausch M. J. , Wang L.‐H. 
Published: January 2005

AbstractExhaustive methylation of 1‐phenylurazole (1), using ethereal diazomethane as the methylating agent, results in the formation of three products: 1‐phenyl‐3,5‐dimethoxy‐1,2,4‐triazole (2), 1‐phenyl‐3‐methoxy‐4‐methyl‐Δ2‐1,2,4‐triazolinev5‐one (3) and 1‐phenyl‐2,4‐dimethylurazole (4). Based on the amounts of 2–4 isolated, the overall yields in these reactions are typically >90%. When 1 and diazomethane were allowed to react in a fashion that resulted in the formation of monomethylated analogues of 1, 1‐phenyl‐3‐methoxy‐Δ2‐1,2,4‐triazoline‐5‐one (5) and 1‐phenylv2‐methylurazole (6) were formed. In separate experiments, the monomethylated species 5 and 6 were allowed to react with diazomethane in efforts to develop a sequence of reactions that reasonably accounts for the formation of 2–4. Whereas N‐ and O‐methylated products were obtained when 5 was treated with ethereal diazomethane, the reaction of 6 and diazomethane produced only the N‐alkylated product 1‐phenyl–2,4‐dimethylurazole (in quantitative yield). The outcomes of these experiments are consistent with a sequence of reactions in which the treatment of 1 with diazomethane results, initially, in the formation of the monomethylated species 5 and 6. In the presence of sufficient diazomethane, 5 and 6 then undergo further mothylation, forming the dimethylated species 2–4.
Oxidation kinetics of p‐aminodiphenylamine with peroxydisulphate
Authors: El‐Sheikh M. Y. , Salem M. A. , Ismail A. A. , Zaki A. B. 
Published: January 2005

AbstractThe kinetics of oxidation of p‐aminodiphenylamine with the peroxydisulphate ion were investigated spectrophotometrically. The oxidation was accompanied by the appearance of a wine‐red colour, which changed to become colourless. The reaction rate was measured by the stopped‐flow technique with a UV spectrophotometer. The reactions proceeded with second‐order kinetics, first‐order for each individual reactant. Cationic micelles (cetyltrimethyl ammonium bromide) caused an enhancement in the reaction rate followed by inhibition at higher concentrations. Anionic micelles (sodium dodecyl sulphate), on the other hand, had a slightly retarding effect. The effects of radical scavenger, pH and ionic strength on the fast oxidation rate were examined. A mechanism consistent with the observations is discussed.