Wydział Chemii

Piotr Durlak

Zdzisław Latajka

2019

Journal of Computational Chemistry

40

671-687

10.1002/jcc.25753

Naukowa

Angielski

Artykuł

Car‐Parrinello and path integrals molecular dynamics (CPMD and PIMD) simulations were carried out for the 10π‐electron aromatic systems: 2‐hydroxy‐2,4,6‐cycloheptatrien‐1‐one, commonly known as Tropolone (I) and 2‐hydroxy‐2,4,6‐cycloheptatriene‐1‐thione, called Thiotropolone (II) in vacuo and in the solid state. The extremely fast proton transfer (FPT) and “prototropy” tautomerism in the keto‐enol (thione‐enethiol) systems have been analyzed on the basis of CPMD and PIMD methods level. Comparisons of two‐dimensional (2D) free‐energy landscapes of reaction coordinate δ‐parameter and R_O…O or R_O…S distances shows that the OH… tautomer to be more favorable in the Thiotropolone. The hydrogen between the oxygen and the sulfur atoms adopts a starkly asymmetrical position in the double potential well. The values of the energy barriers for the FPT were calculated and suggested a strong hydrogen bond with low barrier for FPT mechanism. These studies and the 2D average index of π‐delocalization 〈λ〉 landscape of time evolutions of R_O1…O2 and R_C7O2 or R_C7S1 distances for the both crystals indicate that hydrogen bonds in the crystals of Tropolone (I) and Thiotropolone (II) have characteristic properties for the type of bonding model resonance‐assisted hydrogen bonds and also low‐barrier hydrogen bonds. In the crystal of the Thiotropolone (II), we found the hydrogen bond OH…S existing without the equilibrium of the two tautomers whereas in the crystal of the Tropolone (I) has been confirmed the hydrogen bond OH…O existing with the equilibrium of the two tautomers. It was also found the significant differences in frequency, speed, and the image of the FPT in the studied crystals.

tropolone, thiotropolone, fast proton transfer, resonance-assisted hydrogen bond, low-barrier hydrogen bond

https://dx.doi.org/10.1002/jcc.25753

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