Theoretical Studies on the Intramolecular Hydrogen Bond and Tautomerism of 8-Mercaptoquinoline in the Gaseous Phase and in Solution Using Modern DFT Methods

Abstract

A theoretical quantum chemical study of the intramolecular hydrogen bonding interactions in 8-mercaptoquinoline has been carried out. Special attention has been paid to the rotation of S-H bond and intramolecular proton-transfer reactions. Therewith, the B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p), MPW1K/6-311++G(d,p), MPW1K/6-31+G(2d,2p), BH&HLYP/6-311++G(d,p), and G96LYP/6-311++G(d,p) methods have been used. By means of the Onsager and PCM reaction field methods, the effects of solvent on hydrogen-bond energies, conformational equilibria, rotational barriers, and tautomerism in aqueous solution have been studied. These simulations were done at the MPW1K/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels. Natural-bond orbital analysis has been performed to study the intramolecular hydrogen bond (IHB) in the gaseous phase and in aqueous medium. The stability of forms under consideration in solution does not coincide with that in the gaseous phase, underlining a great importance of the electrostatic influence of solvent. Double-proton transfer in the prototropic tautomerization of 8-mercaptoquinoline, one water molecule complex in the gaseous phase and in solution, has been systematically studied. The double-proton transfer occurs concertedly and synchronously. The water-assisted tautomerization is kinetically less, but thermodynamically more favorable, compared to that of the single-proton transfer. As in the case with single-proton transfer, for water-assisted reaction, the tautomerization energies and barrier heights decrease with the increase in dielectric constant, which implies faster and more complete tautomerization of 8-mercaptoquinoline in a polar solvent.

TD–DFT investigation of the potential energy surface for Excited-State Intramolecular Proton Transfer (ESIPT) reaction of 10-hydroxybenzo[h]quinoline: Topological (AIM) and population (NBO) analysis of the intramolecular hydrogen bonding interaction

“…A comparison of results of different basis sets reflects that most crucial achievement of H-bond energy comes with this basis set. This observation reasonably complies with other reports [37]). We have exploited the 6-311þþG(d,p) basis set for calculation considering the necessity of diffuse functions for full characterization of the hydrogen bond interaction [32b,33-37].…”

Electronic structure of planar-quasicycled organic molecules with intramolecular hydrogen bond

“…As for the molecules XXXIX, XL, the tendencies in IHB effect on the electron structure of molecules revealed in the present work coincide with those found at the higher theory levels: B3LYP/6-31G(d,p), B3LYP/6-31+G(2d,2p), B3LYP/6-311++G(d,p), MPW1K/6-31+G(2d,2p), MPW1K/6-311++G(d,p), MPW1K/6-311++G(2d,3p)//MPW1K/6-311++G(d,p), BH&HLYP/6-311++G(d,p), G96LYP/6-311++G(d,p), including the use of natural bond analysis (NBO). 18,19 The latter testificies to the correctness of the results of the present work.…”

Evidence of coupled photoinduced proton transfer and intramolecular charge transfer reaction in para-N,N-dimethylamino orthohydroxy benzaldehyde: Spectroscopic and theoretical studies

“…Since the first observation of dual fluorescence in methyl salicylate (MS) by Weller in 1956 [1], a variety of molecular systems have been studied experimentally and theoretically for the possibility of ESIPT reaction [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Significant interest rests on the fundamental investigation and the application of organic molecules exhibiting ESIPT reaction because of their four-level photophysical process, and a large Stokes shifted characteristics fluorescence emission band.…”