Tautomerism and aromaticity in 1,2,3-triazoles: the case of benzotriazole (original) (raw)
Related papers
About the benzotriazole tautomerism: an ab initio study
Journal of Molecular Structure: THEOCHEM, 2003
The tautomeric equilibrium of benzotriazole was investigated using Hartree-Fock (HF), MP2, B3LYP and coupled cluster methodologies with a series of basis set. The HF and MP2 results present a clear preference for the 1H and 2H tautomers, respectively, while with B3LYP and coupled cluster both structures have a very similar energy. The inclusion of zero point energy was proved to be necessary when using B3LYP and coupled cluster methods, leading to a preference for the 1H tautomer. The geometric parameters obtained with MP2 and B3LYP using aug-cc-pVTZ basis set are very similar to experimental data of 1H. The frequencies also provided a great concordance with experimental data with the correct use of scale factor. Dipole moment and rotational constants were also analysed. q
Computational and Theoretical Chemistry, 2013
We have studied the 1,2,3-triazole system with a set of 25 substituents of different electronic features using several methods. Our aim is to find out a calculation method for the analysis of these molecules in biological systems. The combined AIM and NBO study permitted us to justify the observed tautomeric preferences. The absolute predominance of the 2H-tautomer forms is greatly changed when the substituent group possesses anionic character; therefore the pH of the medium is relevant. When the calculations were carried out in solution, noteworthy changes in the behavior of charged substituents were observed. These facts may be relevant when studying the interactions of these molecules with biological receptors. Keyword 1,2,3-triazol, tautomerism, NBO analysis, AIM charges, group electronegativity, resonance. interactions as concerned in Van der Waals or π-staking. 2. Material and methods Calculations were performed using Gaussian 03W version 6.1 [11]. Optimized geometries were calculated at MP2 [12], B3LYP [13], MPW1PW91[14] and MPWB1K [15] level of theory using 6-31+G* basis set. In addition 6-311++G* basis set was used for specific hydrogen bond analysis. Electronic densities obtained at partial and full MP2/6-311++G* and MPW1PW91/6-311++G* levels served as input for Atom in Molecules (AIM) [16] Bader analysis helped with the AIM2000 [17] program. Natural Resonance Theory Analysis (NRT) was performed using NBO5.0 [18] program. 3. Results and discussions 3.1. The influence of C-substituents in 1,2,3-triazoles (gas phase) on the tautomeric equilibrium Unsubstituted 1,2,3-triazole can exist in two tautomeric forms: the 1H-tautomer, with C s symmetry, and the 2H-tautomer with C 2v symmetry. The presence of a 5(4)-substituent increases the number of these forms at three, or even more, if the substituent group is OH, NH 2 or SH (Scheme 1. In brackets the nomenclature used in this work). The investigation of tautomeric equilibrium in triazoles has been usually focused on Nsubstituted derivatives [19] rather of C-substituted derivatives[20-24]. Oziminski et all performed the most complete study on 5(4)-substituted-1,2,3-triazole systems with a quite high basis sets and DFT (B3PW91/6-311++G**) [24]. A higher level of calculus (CCSD(T)/CBS) for the two unsubstituted imidazole tautomers was reported by Denis [25] Scheme 1. 1,2,3 triazole nomenclature
Tetrahedron, 2010
The properties of 28 molecules together with 12 transition states belonging to the series of azido-azines, tetrazolo-azines, diazo-azines, and 1,2,3-triazolo-azines have been studied at the B3LYP/6-31G(d), B3LYP/ 6-311þþG(d,p) and, for 26 cases, at the G3B3 level. Energies, NICS and bond critical points were used to discuss the ring-chain tautomerism of these compounds in relation with the aromaticity of the azines (pyridine, pyrimidine, quinazoline, 1,3-diazapyrene, and perimidine) and the azoles (tetrazoles and 1,2,3-triazoles).
Journal of Molecular Modeling, 2020
Density functional theory investigations at the DFT-B3LYP/6-311++G ** theoretical level employed to determine the tautomerism, substituent effects of 4-substituted 4-amino-5-methyl-2,4-dihydro-3H-1,2,4-triazole-3-thione, and its derivatives (4-R-H, 4-R-CH 3 , 4-R-F, 4-R-NO 2) in the selected solvent (acetone, acetonitrile, and dichloromethane) and gas phases using the polarizable continuum method (PCM) model. The substituted 1,2,4-triazoles have two main different tautomers namely N 2-H and S 7-H. For considered derivatives, thione forms are more energetically stable and dominant form in the studied solvent and gas phases. In addition, geometrical parameters, charges on atoms, dipole moments, energetic properties, and the nucleus-independent chemical shifts (NICS) are investigated. It has been seen that these molecular features of the studied compound and its derivatives are mostly solvent dependent. For electron-releasing and-withdrawing derivatives in the solution and gas phases, 2-H forms are the more stable and dominant form. The relative stability of the C 4-substituted 1,2,4-triazole tautomerism is influenced by the possibility for intramolecular interactions between substituent and electron-donor or electron-acceptor centers of the triazole ring.
Journal of Molecular Modeling, 2010
The one step intramolecular thione-thiol tautomerism of 1,2,4-triazole-3-thione and its disubstituted derivatives has been studied through the use of electronic structure methods. Due to the absence of experimental data for the parent molecule of 1,2,4-triazole-3-thione the structure and energetics of aforementioned tautomers were derived using various basis sets and levels including HF, B3LYP, and MP2 methods. The gas phase results show that in all different levels of theory the most stable tautomer is the thione form. It has also been revealed that B3LYP/6-31G(d,p) level is quite well suited and reliable to investigate these kinds of tautomerism. To account the influence of substituents on the mentioned tautomerization, the tautomerism and conformational properties as well as vibrational analysis of 20 halophenyl and isopyridyl derivatives were investigated using B3LYP/6-31G(d,p) calculations. In all cases the calculations indicate that substituents have no considerable effects on relative stabilities and energy barriers for the thione-thiol proton transfer and the thione forms are the predominant species in the gas phase. In order to figure out the relative stabilities of the species involved in the tautomerism, geometrical and natural bond orbital (NBO) analyses have been employed. It has also been shown that the computed vibrational frequencies of tautomers with different scaling factors could be used to interpret the vibrational frequencies in IR spectrum of similar species.
Tautomerism in the Fused N‐Rich Triazolotriazole Heterocyclic System
Tautomerism in the 2,triazolo [3,2-c][1,2,4]triazole fused aromatic system has been investigated by single-crystal Xray analysis, UV/Vis spectroscopy and theoretical calculations on selected new heterobicycle derivatives. The reactions of 3,4-diamino-1,2,4-triazoles with acyl chlorides or acetic anhydride in pyridine at reflux led to ring closure and the fused aromatic system was obtained as the secondary amide at N2 instead of at N5 as previously reported in the literature. For the [1,2,4]triazolo[3,2-c][1,2,4]triazole system, three different tautomers can be present. Crystal structure [a]
Russian Journal of General Chemistry, 2008
Compounds capable of tautomerism: sulfanyl-1,2,4-triazole, its C-phenyl derivative, and the crystal hydrate of the latter, were studied by single crystal X-ray diffraction. In the crystals they exist in the form of 3-R-1(H),4(H)-4,5-dihydro-1,2,4-triazole-5-thione with a considerable contribution of the bipolar structure. Published data on the tautomerism of sulfanyl-1,2,4-triazoles and their N-substituted analogs and on the correlation between the spectral characteristics and structures of sulfanyl-1,2,4-triazoles capable of tautomerism are discussed.
The tautomerism of 1,2,3-triazole, 3(5)-methylpyrazole and their cations
Journal of Computational Chemistry, 1989
The annular tautomerism of 1,2,3-triazole and 3(5)-methylpyrazole is discussed by means of a combination of theoretical calculations and experimental (ICR) gas-phase basicities and acidities. In the gas phase 1,2,3-triazole exists as the ZH-tautomer, whereas both tautomers of 3(5)-methylpyrazole are of similar energy. The solvent effects on these prototropic equilibria are discussed taking into account solvent properties as polarity/polarizability, acidity, and basicity. In nonhydrogen bonding solvents, the difference in dipole moments between both tautomers plays a role that has usually been underestimated.