共查询到20条相似文献,搜索用时 15 毫秒
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V. Yu. Vvedenskii E. D. Shtefan R. N. Malyushenko E. V. Shilkin É. N. Deryagina 《Chemistry of Heterocyclic Compounds》1997,33(9):1047-1061
The substitutent effect on the self-thiylation of 2-thiophenethiols was studied. Experimental results and quantum chemical calculations suggested possible mechanisms for this reaction dependent on the reaction conditions.Irkutsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of Russia, 664033 Irkutsk, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1203–1218, September, 1997. 相似文献
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C. Y. Yuan S. S. Li H. Z. Feng W. H. Hu X. G. Liao 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):235-238
Abstract An empirical approach for the estimation of substituent polar and steric parameters of organophosphorus compounds was suggested by experimental measurements and theoretical calculations. 相似文献
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The keto-enol equilibrium of 2-methoxycarbony1-3-oxo-4-methy1-8-oxabicyclo [3,2,1]-octane is dramatically affected by the stereochemistry of the 4-methyl group. 相似文献
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In our recent work towards the nontarget identification of products of nucleic acid (NA) damage in urine, we have found previous
work describing the dissociation of NA bases not adequate to fully explain their observed reactivity. Here we revisit the
gas-phase chemistry of protonated uracil (U) during collision induced dissociation (CID) using two modern tandem mass spectrometry
techniques; quadrupole ion trap (QIT) and quadrupole time of flight (Q-TOF). We present detailed mechanistic proposals that
account for all observed products of our experiments and from previous isotope labeling data, and that are supported by previous
ion spectroscopy results and theoretical work. The diverse product-ions of U cannot be explained adequately by only considering
the lowest energy form of protonated U as a precursor. The tautomers adopted by U during collisional excitation make it possible
to relate the complex reactivity observed to reasonable mechanistic proposals and feasible product-ion structures for this
small highly conjugated heterocycle. These reactions proceed from four different stable tautomers, which are excited to a
specific activated precursor from which dissociation can occur via a charge-directed process through a favorable transition
state to give a stabilized product. Understanding the chemistry of uracil at this level will facilitate the identification
of new modified uracil derivatives in biological samples based solely on their reactivity during CID. Our integrated approach
to describing ion dissociation is widely applicable to other NA bases and similar classes of biomolecules. 相似文献
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Duncan M. A. Grieve Graham E. Lewis Michael D. Ravenscroft Peter Skrabal Takaaki Sonoda Ivanka Szele Heinrich Zollinger 《Helvetica chimica acta》1985,68(5):1427-1443
The thermal N2 exchange of a number of 15N-labelled diazo compounds was studied in solution. The compounds involved were 3-diazo-1-methylindolin-2-one ( 1 ), 9-diazofluorene ( 2 ), 5-diazo-1,3-cyclopentadiene-1,2,3,4-tetracarbonitrile ( 3 ), 2-diazo-2H-imidazole-4,5-dicarbonitrile ( 4 ), 4-diazocyclohexa-2,5-dienone ( 5 ), and the conjugate acids of 4 and 5 , namely 4,5-dicyano-1H-imidazole-2-diazonium ion ( 6 ) and 4-hydroxybenzenediazonium ion ( 7 ). Only 1 , 4 , 6 , and 7 exchange their diazo group with ‘external’ molecular N2. The results are explained on the hypothesis that only organic species which have an empty σ orbital and which are effective in π electron back-donation are able to react with N2. Thus, reaction with carbenes is likely to occur only if the carbene is in the 1A2 singlet state and if its electrophilicity is high. 相似文献
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Well-resolved absorption spectra of benzoic acid and its derivatives with one hydrogen atom replaced by a substituent group CH3, OH, NH2 or NO2 were reported in the frequency region between 6 and 67 cm^-1 at room temperature with terahertz time-domain spectroscopy (THz-TDS). These substances can be distinguished easily based on the terahertz absorption spectra. The measurements suggested that even minor changes in the molecular configuration and chemical composition lead to distinct differences in THz spectrum. Density functional theory (DFT) method was used to assist the analysis and assignment of the individual THz absorption spectra of benzoic acid and its methyl derivatives. Observed THz responses of samples can be assigned to the collective vibrations associated with intermolecular hydrogen bonds. 相似文献
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Derivatives of 2-chloro-2′-deoxyadenosine ( 1a ) containing secondary 6-NH2 groups ( 5a-c ) or a 8-Br substituent ( 9 ) were synthesized. They were tested together with ring-modified congeners containing a pyrrolo[2,3-b]pyridine, pyrrolo[3,2-c]pyridine, or pyrazolo[3,4-d]pyrimidine ring system as inhibitors of various leukemic cell lines. Only the 8-Br derivatives 9 showed inhibitory activity, whereas the base-modified congeners were not active. Compound 1a was protonated at a pKa = 1.4 (2′-deoxyadenosine at pKa = 3.8). Protonation occurred at N(7) and not at N(1) as observed for dA. 相似文献
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I. Ya. Mainagashev V. V. Lapachev M. A. Fedotov V. P. Mamaev 《Chemistry of Heterocyclic Compounds》1987,23(12):1339-1342
The tautomeric equilibria of acylmethylpyrazines and -quinoxalines in chloroform were studied by 1H, 14N, and 17O NMR spectroscopy. It was shown that keto-enol tautomerism is realized in the acylmethylpyrazine series. Annelation leads to the development of an ylidene tautomer in the acylmethylquinoxaline series. A marked dependence of the position of the intrachelate equilibrium on the character of the solvent was observed.See [1] for Communication 15.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1663–1667, December, 1987. 相似文献
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M. I. Batuev 《Russian Chemical Bulletin》1959,8(11):1938-1941
Summary Dual reactivity in substances is due to the tautomerism of molecules in accordance with Scheme I or (particularly in cases previously assigned to the field of pseudomerism) to the tautomerism of intermediate ions and radicals in accordance with Scheme III in, in which the tautomeric forms (molecules, ions, radicals) have separate existences. These particles, which exist separately in a state of equilibrium reversible isomerization, can give two series of derivatives under the appropriate conditions, and this is confirmed by physical investigation of the matter [12].This paper is published as a polemic contribution. 相似文献
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GabrielaL. Borosky 《Helvetica chimica acta》2001,84(12):3588-3599
The opening reaction of S‐protonated polycyclic aromatic hydrocarbon episulfides has been evaluated by means of ab initio, density‐functional, and semiempirical calculations. Episulfides are predicted to open more easily than the corresponding O‐protonated derivatives, epoxides, and diol epoxides. On the other hand, diol episulfides would present the slowest rate for opening, the syn isomers being expected to be more reactive than the anti isomers. Bay‐region and methyl‐substituted bay‐region compounds were found to open more readily among the sulfur derivatives, following the same reactivity pattern as the oxygen analogs. The exothermicity of the opening process correlated with the charge delocalization in the resulting carbocation. This reaction step is very important in the carcinogenic pathway of the epoxide analogs. Thus, according to the present calculations, episulfides could possibly exert carcinogenic activity. 相似文献
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Semiempirical (MINDO/3, AM1, PM3, MNDO) and ab initio (4-31G and 4-3IG + dAO/S basis sets) calculations on the relative stabilities and structures of the five potential tautomeric forms of rhodanine are reported. It is shown that all methods (excepting PM3) predict as most stable 2-thioxo-4-thiazolidinone. These results correspond to the known experimental data. The infrared spectrum of rhodanine was recorded for the region 4000-150 cm–1, and the characteristic bands were compared with AM1 and 4-31G + dAO/S calculated frequencies. The transition states between five pairs of all possible tautomeric forms of the rhodanine were found by the AM1 method. 相似文献
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Chiappe C De Rubertis A Jaber A Lenoir D Wattenbach C Pomelli CS 《The Journal of organic chemistry》2002,67(20):7066-7074
Sterically congested adamantylideneadamantanes (1b-g) (X = Br, Cl, F, OH, OEt, OCOCH(3)), homoallylically substituted with equatorial groups (X), react with bromine in 1,2-dichloroethane to give a stable bromonium ion intermediate or a substitution product depending on the nature of the substituent and on the bromine concentration. The nature of the substituent markedly affects the formation constant of the 1:1 pi-complexes, as well as of the formation constant and reactivity of bromonium ion intermediates. The different reactivity of the ionic intermediates, which depends on the nature of substituents, is attributed to bromonium or bromocarbenium character of the intermediate, with the support of theoretical investigations. Ab initio calculations on 1:1 adamatylideneadamantane-Br(2) complexes (2a-f) show that the substituent affects the stability of these species through electrostatic and dispersion effects. Solvent effects may also contribute to modulate the relative stability of these species. 相似文献
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N. P. Bednyagina G. N. Lipunova G. M. Petrova 《Chemistry of Heterocyclic Compounds》1973,9(5):643-645
The structures of new symmetrical and asymmetrical 1,5-dibenzazolylformazans were investigated by IR and electronic spectroscopy. It is shown that 1,5-dibenzimidazolylformazans, regardless of the substituent in the 3 position (methyl, phenyl), display the presence of the tautomeric imino form in solutions. 1,5-Dibenzothiazolylformazans display a high tendency to form chelate forms. The stability of the chelate increases on passing from the 3-methyl to the 3-phenyl derivative.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 699–701, May, 1973. 相似文献
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V. V. Negrebetskii A. F. Grapov L. V. Razvodovskaya N. N. Melnikov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract The reaction of phosphorylation of aminoheterocycles [aminodihydro(iminotetrahydro)-1,3-thiazines, amino(imino)-thiasoli (di)nes, amino (imino)pirroli (di) nes, isoindol (en)- ines] has been studied by means of NMR 1H, 13C, 31P spectroscopy. The processes of intra- and intermolecular migrations of the phosphoryl groups PIV between endo- and exo-cyclic nitrogens have been detected and examined. 相似文献
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Described are the design, synthesis, and structures of three nonpolar nucleoside isosteres to be used as probes of noncovalent bonding in DNA and as isosteric replacements for the natural nucleosides in designed nucleic acid structures. Reaction of substituted aryl Grignards with 3',5'-bis-O-toluoyl-α-deoxyibofuranosyl chloride and subsequent deprotection with sodium methoxide in methanol afforded the two β-C-nucleoside pyrimidine analogs 1 and 2. The dimethylindolyl nucleoside 3, a purine isostere, was obtained by a nucleophilic displacement on α-chlorodeoxyribofuranose by the sodium salt of 4,6-dimethylindole, followed by deprotection. Regio- and stereochemistry of the products were established with NOE difference spectra and (1)H NMR splitting patterns. Analogs 1 and 2 are nonpolar isosteres of thymidine, and nucleoside 3 is an isostere of 2-aminodeoxyadenosine, the triply-bonded Watson-Crick partner of thymidine. Semiempirical AM1 calculations were carried out to provide bond length information to assess structural similarities between the isosteres and their natural counterparts. 相似文献