Structures, Energetics, and Spectra of (NH) and (OH) Tautomers of 2-(2-Hydroxyphenyl)-1-azaazulene: A Density Functional Theory/Time-Dependent Density Functional Theory Study

Abstract

Tautomerization of 2-(2-hydroxyphenyl)-1-azaazulene ( 2OHPhAZ ) in the gas phase and ethanol has been studied using B3LYP, M06-2X, and ωB97XD density functional theory (DFT) with different basis sets. For more accurate data, energies were refined at CCSD(T)/6-311++G(2d,2p) in the gas phase. Nuclear magnetic resonance (NMR), aromaticity, Fukui functions, acidity, and basicity were also calculated and compared with experimental data. Time-dependent density functional theory (TDDFT)-solvation model based on density (TDDFT-SMD) calculations in acetonitrile have been utilized for the simulation of UV–vis electronic spectra. In addition, electronic structures of the investigated system have been discussed. The results reveal that the enol form ( 2OHPhAZ ) is thermodynamically and kinetically stable relative to the keto tautomer ( 2OPhAZ ) and different rotamers ( 2OHPhAZ–R1:R3 ) in the gas phase and ethanol. A comparison with the experiment illustrates a good agreement and supports the computational findings.

DFT study, and natural bond orbital (NBO) population analysis of 2-(2-Hydroxyphenyl)-1-azaazulene tautomers and their mercapto analouges

“…In ethanol, the order of stability becomes thione > thiol > R1(S) > R3(S) > R2(S) in 2MPhAZ. Our results are agreeing with the previous results that of 2-(2-Hydroxyphenyl)-1-aza azulene and 2-(2-Mercaptophenyl)-1-aza azulene 5 , 8 .…”

“…This shows that increasing the Hammett constants of these studied compounds leads to a decrease in charge transfer energy. It may be concluded that the strength of the O(S)-C bond only minimally changes in the studied compounds because the amount of destabilization energy predicted using the NBO technique does not significantly alter in each of the compounds, which is consistent with our calculated results 5 and the experimental results 25 .…”

“…The aim of this study is complementary to our work which is published in omega and Scientific reports journals 5 , 8 to complete our work in this point that we study with the Natural Bond Orbital property to find the mechanism of the stability of the tautomer and rotamers of 2-hydroxyl phenyl azaazulene and -mercapto phenyl azaazulene.…”

“…A reasonably substantial absorption in the visible light spectrum, as well as the X-ray diffraction data 4 , support the presence of its aromatic and coplanar nature and an intramolecular hydrogen bond. The stability of 2OHPhAZ, the keto tautomer (2OPhAZ), and various rotamers (2OHPhAZ-R1:R3) in the gas phase and ethanol was the subject of DFT research by El-Meligy et al 5 . Furthermore, to the best of our experience, we have not found any analysis of the nature of the bonding in the tautomerization of 2-(2-Hydroxyphenyl)-1-azaazulene (2HPhAZ) and its mercapto analogue 2-(2-Mercaptophenyl)-1-azaazulene (2MPhAZ).…”

Isosterism in pyrrole via azaboroles substitution, a theoretical investigation for electronic structural, stability and aromaticity

“…In the investigated NB system, NICSzz and HOMA calculation were performed at the B3LYP/6-311 + G(d,p) level provide a good match with previous studies on pyrrole [ [115] , [116] , [117] ]. During moving from first group to second group isomers, both NICS (1) zz and HOMA indices show good results with the decreasing order of aromaticity.…”