Concerted and asynchronous mechanism of ground state proton transfer in alcohol mediated 7-hydroxyquinoline

Reaction pathway and H/D kinetic isotope effects of the triple proton transfer in a 7‐hydroxyquinoline‐methanol complex in the ground state: A computational approach

“…This asynchronous concerted mechanism is consistent with the results of the previous study by Kang et al, who studied the reaction pathways of 7HQ(MeOH) 2 at the M06-2X/6-311 + G** level with the polarizable continuum model for solvation by heptane. [16] As shown in Table 2, the distances between the moving H atom (H1, H2, or H3) and the donor or acceptor atom at the TS obtained in the present B3LYP/6-31G* calculation are similar to the corresponding distances reported by Kang et al although the present calculation takes a lower computational cost. An asynchronous concerted triple PT has also been reported for the reaction of ClONO 2 and HCl mediated with 2 H 2 O molecules in the gas phase.…”

“…The calculated barrier for the present system varied with the calculation method, as shown in Table 1. On the other hand, the geometries of the TS are similar to each other with the B3LYP/6-31G* and M06-2X/6-311 + G** [16] methods as shown in Table 2.…”

“…The geometries are similar to those reported in previous studies. [8,16] The H-bond between O and O1 in the reactant seems to be stronger than the others in both the reactant and product. Judging from the donor-acceptor distances (2.8-2.9 Å for the oxygen-oxygen pairs and 2.9-3.0 Å for the nitrogen-oxygen pairs), all the H-bonds are medium rather than shortstrong in both the reactant and product.…”

“…Because of the high complexity of such systems, simple models have been extensively studied to understand the mechanism and dynamics of multiple PT in various environments at the molecular level. For example, 7-azaindole [1][2][3][4][5][6] and 7-hydroxyquinoline (7HQ) [7][8][9][10][11][12][13][14][15][16] have been investigated, both experimentally and theoretically, as biomimetic models. When excited by UV irradiation, these compounds are converted to their tautomers via multiple PT mediated by protic molecules such as H 2 O, alcohol, and NH 3 .…”

“…Recently Kang et al investigated the reaction pathway for the GSPT in 7HQ·(ROH) 2 by density functional theory (DFT) calculations and revealed that the GSPT in 7HQ·(ROH) 2 takes place with an asynchronous concerted mechanism, in which the 3 protons are transferred sequentially (ie, asynchronously) in a single step. [16] They estimated the rate constants based on the transition state theory (TST) and assumed that the tunneling effect is not significant. In general, tunneling effect on reaction rates may be important when the transfer of a light particle such as proton is involved in the rate-determining step.…”