Investigations of the hydrogen bond in the crystals of tropolone and thiotropolone via car‐parrinello and path integral molecular dynamics

Abstract

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 RO…O or RO…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 RO1…O2 and RC7O2 or RC7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. © 2018 Wiley Periodicals, Inc.

Electronic Structure, Aromaticity and Optical Properties of Dehydro[10]annulene

“…Doering and Detert established the first rule of aromaticity in 1951‐the (4n+2) rule. This rule states that a cycloene with (4n+2) π electrons (where n is an integer) is aromatic [6] . The aromatic system is a circular closed conjugated system, [7,8] π electron is highly delocalized, has delocalization energy, system energy is low, relatively stable [9] .…”

“…This rule states that a cycloene with (4n + 2) π electrons (where n is an integer) is aromatic. [6] The aromatic system is a circular closed conjugated system, [7,8] π electron is highly delocalized, has delocalization energy, system energy is low, relatively stable. [9] Aromaticity cannot be directly measured by any physical or chemical experiment.…”

Low-Barrier Hydrogen Bond in Fujikurin A–D: A Computational Study

“…We used MC_MO methods to successfully evaluate the effects of NQEs and H/D isotopes in different hydrogen-bonded systems and proton transfer reactions. PIMD can also consider NQEs statistically within the Born–Oppenheimer approximation framework. − ,− The PIMD approach considers NQEs as well as thermal effects. Many PIMD studies have been used to understand NQEs in the context of hydrogen-bonded systems, including LBHBs.…”

Evidence of IR-Induced Chemistry in a Neat Solid: Tautomerization of Thiotropolone by Thermal, Electronic, and Vibrational Excitations

“…Besides our study, only a few additional investigations have been reported, most of them using theoretical approaches. These studies have predicted the thione-enol tautomeric form of TT as being predominant in the gas phase as well as in aqueous solution and the solid state . However, there is still a lack of experimental data.…”

“…These studies have predicted the thione-enol tautomeric form of TT as being predominant in the gas phase 48 as well as in aqueous solution 48 and the solid state. 49 However, there is still a lack of experimental data. The most relevant previously reported experimental results refer to the compound in solution and in the solid state, where Machiguchi et al claimed that TT exists as two rapidly equilibrating tautomeric (thione-enol and thiol-keto) structures.…”