Annular Tautomerism Research Articles

ChemInform Abstract: A SUBSTITUENT CORRELATION AND MEDIUM EFFECTS ON THE ANNULAR TAUTOMERISM OF SUBSTITUTED 5‐ARYLTETRAZOLES: THE NITROGEN ANALOGS OF BENZOIC ACIDS. A CARBON‐13 NMR AND DIPOLE MOMENT STUDY

Chemischer InformationsdienstVolume 15, Issue 29 Article ChemInform Abstract: A SUBSTITUENT CORRELATION AND MEDIUM EFFECTS ON THE ANNULAR TAUTOMERISM OF SUBSTITUTED 5-ARYLTETRAZOLES: THE NITROGEN ANALOGS OF BENZOIC ACIDS. A CARBON-13 NMR AND DIPOLE MOMENT STUDY R. N. BUTLER, R. N. BUTLERSearch for more papers by this authorV. C. GARVIN, V. C. GARVINSearch for more papers by this authorH. LUMBROSO, H. LUMBROSOSearch for more papers by this authorC. LIEGEOIS, C. LIEGEOISSearch for more papers by this author R. N. BUTLER, R. N. BUTLERSearch for more papers by this authorV. C. GARVIN, V. C. GARVINSearch for more papers by this authorH. LUMBROSO, H. LUMBROSOSearch for more papers by this authorC. LIEGEOIS, C. LIEGEOISSearch for more papers by this author First published: July 17, 1984 https://doi.org/10.1002/chin.198429071AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue29July 17, 1984 RelatedInformation

A substituent correlation and medium effects on the annular tautomerism of substituted 5-aryltetrazoles: the nitrogen analogues of benzoic acids. A carbon-13 n.m.r. and dipole moment study

The annular tautomerism of substituted 5-phenyltetrazoles shows a linear correlation of log KT{KT=[N(1)H]/[N(2)H]} with the Hammett σ values of para-substituents. The tautomerism favours the 1H-form but electron-withdrawing substituents displace the equiliblium towards the 2H-form. Solvent dielectric permittivity and temperature effects also influence the annular tautomerism. A change of solvent from dimethyl sulphoxide to dioxane and an increase in temperature had similar effects in orienting the tautomerism towards the 2H-form, but the temperature effect was relatively small. Carbon-13 n.m.r. shifts and dipole moment analyses of the tautomerism gave complementary results.

Conformational studies by dynamic nuclear magnetic resonance spectroscopy. Part 27. Kinetics and mechanism of annular tautomerism in isomeric triazoles

The rates for the prototropic shift of the NH hydrogen in the two isomeric triazoles [(1)= 1,2,4- and (2)= 1,2,3-triazole] have been measured at low temperature by 1H n.m.r. (100 and 300 MHz). Only the less symmetric (cs) of the two possible annular tautomers was found to be populated in the case of (1), whereas both (cs and c2v) were detected in (2). The relative proportions in the latter compound are dramatically dependent on temperature, concentration, and solvent. In either triazoles the kinetic process appears to be intramolecular and the mechanism corresponds to a 1,2 prototropic shift. The parameters of activation yielded similar ΔH‡(5.8 and 6.5 kcal mol–1) and quite negative ΔS‡(–29 and –19 cal mol–1 K–1) values, thus indicating a relatively low probability of attaining the ordered (three-membered) cyclic transition state.

13C NMR Study of Annular Tautomerism of Azoles in the Solid State

Etude par spectrometrie RMN de 13 C de la tautomerie prototropique des triazole, tetrazole, indazole, benzimidazole et benzotriazole, de la tautomerie de fonction de la benzoxazolidinethione-2, et du tautomerisme non prototropique du trimethylsilyl-1 benzimidazole

A theoretical and experimental dipole moment study of annular tautomerism in tetrazole

The electric dipole moments of tautomeric 1 H-tetrazole and 2 H-tetrazole have been calculated by the ab initio molecular orbital technique with a 4-31G basis set, and compared with literature experimental values for gaseous C-deuterio-1 H-tetrazole and 2 Htetrazole. Calculated σ and π moments for both tautomers are discussed and compared with previous theoretical values. In 2 H-tetrazole the mesomeric moment outweighs the primary moment corresponding to the classical valence structure, in determining the actual direction of the molecular dipole moment. The calculated total energies are found to be equal for both tautomers. The fact that the dipole moment of tetrazole measured in dioxane (4.88 D) indicates the 1 H form to be the more abundant (78%) is due to a greater Onsager's solvent reaction-field stabilization of the more polar species.

The factors affecting possibility of observation of annular tautomerism in dihydropyrimidine systems

The amount of water in the solvent, microconcentration of H + ions in the solution, paramagnetic impurities, concentration dependence, have remarkable effects on the ability of observing tautomerism in dihydropyrimidines.

ChemInform Abstract: A DIPOLE MOMENT STUDY OF ANNULAR TAUTOMERISM IN 5‐P‐TOLYLTETRAZOLE

Chemischer InformationsdienstVolume 12, Issue 17 Physical Organic Chemistry ChemInform Abstract: A DIPOLE MOMENT STUDY OF ANNULAR TAUTOMERISM IN 5-P-TOLYLTETRAZOLE H. LUBROSO, H. LUBROSOSearch for more papers by this authorJ. CURE, J. CURESearch for more papers by this authorR. N. BUTLER, R. N. BUTLERSearch for more papers by this author H. LUBROSO, H. LUBROSOSearch for more papers by this authorJ. CURE, J. CURESearch for more papers by this authorR. N. BUTLER, R. N. BUTLERSearch for more papers by this author First published: April 28, 1981 https://doi.org/10.1002/chin.198117059Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue17April 28, 1981 RelatedInformation

Annular tautomerism in the solid state: a high resolution n.m.r. study

13 C N.m.r. spectra of solid samples of pyrazole and imidazole were obtained using the ‘magic angle’ spinning technique; both compounds show three separate signals corresponding to Cs structures (no proton exchange).

A study of annular tautomerism, interannular conjugation, and methylation reactions of ortho-substituted-5-aryltetrazoles using carbon-13 and hydrogen-1 n.m.r. Spectroscopy

In ortho-substituted-5-phenyltetrazoles, Ar–CN4H (Ar = 2′-MeC6H4, 2′-ClC6H4, or 2′,6′-Cl2C6H3), the rings are twisted out of the planar configuration and interannular conjugation is inhibited. In each case the tetrazole 1-NH tautomer is strongly predominant. When the rings are coplanar, as in para-substituted-5-phenyltetrazoles, the electron-withdrawing effect of the para-substituents changes the tautomerism significantly back towards the 2-NH form. Methylation of the anion of 5-(ortho-substituted-phenyl)tetrazoles occurred equally at the 1-N- and 2-N-positions, or slightly favoured the 1-N-position, and thereby contrasted with the p-substituted derivatives, where 2-N-methylation strongly predominates.

A dipole moment study of annular tautomerism in 5‐p‐tolyltetrazole

AbstractThe electric dipole moment of 5‐(p‐tolyl)tetrazole in dioxane at 30.0° (4.99 D) suggests that the compound is a mixture of the 1H‐tautomer (60 ± 10%) and the 2H‐tautomer (40 ± 10%) in this medium. This determination was made by taking μ (2H) as μ (2Me) = 2.41 D in benzene, and by taking μ (1H) as μ (1Me) = 6.03 D in benzene with due allowance being made for the presence of interannular conjugation in the 1H‐tautomer but not in the 1‐methyl isomer. The dipole moments of 1‐methyl‐5‐(p‐tolyl)tetrazole and 2‐methyl‐5‐(p‐tolyl)tetrazole were also measured in dioxane; that of 1,5‐trimethylenetetrazole was measured in benzene. Comparison with relevant data for unsubstituted tetrazole has also been made.

A carbon-13 and proton nuclear magnetic resonance study of annular tautomerism and interannular conjugation in some substituted-5-aryl-tetrazoles

A comparison of 13C spectra for a series of substituted 5-phenyltetrazoles, (RC6H4; R = H, p-Me, p-NO2, o-NO2), with their 1-N- and 2-N-methyl derivatives suggested that the tetrazoles exist predominantly in the 1-H form. Both 1H and 13C n.m.r. spectra suggested the presence of interannular conjugation in 5-aryl-2-methyltetrazoles and 5-aryl-1H-tetrazoles. This was either reduced or absent in 5-aryl-1-methyletetrazoles and also in 5-(o-nitrophenyl)-1H-tetrazole.

Systèmes aromatiques à 10 électrons π dérivés de l'aza‐1 pentalene. III. Recherches dans la série du pyrazolo [3,4‐c] pyrazole

AbstractThe annular tautomerism of 3,4‐dimethyl‐6‐phenyl‐pyrazolo [3,4‐c]pyrazole is discussed on the basis of its 13C NMR spectrum and the spectra of two of its methylated and acetylated derivatives.

Annular tautomerism of benzimidazoles: Effect of a hydrogen bond on the prototropic rate

Annular tautomerism of benzimidazoles: Effect of a hydrogen bond on the prototropic rate

Systèmes aromatiques à 10 électrons π dérivés de l'aza-3a-pentalène. XI. Etude par résonance magnétique nucléaire de l'imidazo [1,2-b] pyrazole et du pyrazolo [1,5-a] benzimidazole

Nuclear magnetic resonance spectroscopy has allowed us to determine the annular tautomerism in two [5,5]-heteroaromatic systems and the position of the acetyl group in their acetyl derivatives. In each case, the more stable compound is the one in which the imidazolic nitrogen atom is bearing H or COCH3. We have also found unusual couplings with the N—H in the N-unsubstituted compounds and abnormally high barriers for the azolides. These observations agree well with the hypothesis of a decrease in the aromaticity of the imidazolic part.

Annular tautomerism in nitrogen heterocycles. Part I. Tetrazoles

Download options Please wait... Article information DOI https://doi.org/10.1039/J29690001240 Article type Paper Download Citation J. Chem. Soc. B, 1969, 1240-1244 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Annular tautomerism in nitrogen heterocycles. Part I. Tetrazoles M. Charton, J. Chem. Soc. B, 1969, 1240 DOI: 10.1039/J29690001240 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author M. Charton