Calculation of Kinetic Isotope Effects for Intramolecular Hydrogen Shift Reactions Using Semiclassical Instanton Approach

Abstract

Primary H/D kinetic isotope effects for the [1,5] hydrogen shift reaction in 13-atomic 1,3-pentadiene and [1,7] hydrogen shift reaction in 23-atomic 7-methylocta-1,3,5-triene are calculated using the semiclassical instanton approach. All 33 and 63 internal degrees of freedom, respectively, are treated quantum mechanically with multidimensional tunneling automatically accounted for by the instanton approach. Reactive potential energy surfaces are calculated on-the-fly using mPW1K/6-31+G(d,p) and mPWB1K/6-31+G(d,p) electronic structure methods. The calculated kinetic isotope effects agree well with the previously reported experimental measurements. The analytical expressions of the semiclassical instanton approach allow one to determine quantitative contributions of various physical mechanisms to the calculated kinetic isotope effects. Multidimensional tunneling is found to play important role in both studied hydrogen shift reactions.

Thermally activated tunneling in organic reactions

“…52 (ii) H/D KIEs were computed including tunneling (by means of CVT + μOMT, squares, Figure 9) were lower than experimental (solid circles, Figure 9). 48 When tunneling was accounted for by semiclassical instanton (SI) (solid line, Figure 9), the H/D KIE of the sigmatropic shift were in even better agreement with experimental results. 48 Similar to [1,5]-sigmatropic shifts in Section 5.1.4, here the computational data were fair in reproducing the experimental data.…”

Formation of the prebiotic molecule NH2CHO on astronomical amorphous solid water surfaces: accurate tunneling rate calculations

“…Instanton theory is meanwhile frequently used to calculate reaction rates in different areas of chemistry. 14 , 37 , 53 – 74 …”

Hydrogen transfer reactions of interstellar complex organic molecules

“…The instanton method based on Feynman path integral theory using the semiclassical approximation was used to compute the reaction rate constants (Langer 1967(Langer , 1969Miller 1975;Coleman 1977;Callan Jr. & Coleman 1977;Gildener & Patrascioiu 1977;Affleck 1981;Coleman 1988;Hänggi et al 1990;Benderskii et al 1994;Messina et al 1995;Richardson & Althorpe 2009;Kryvohuz 2011;Althorpe 2011;Kryvohuz 2014;Richardson 2016). For a given temperature, it provides the most probable tunnelling path, the instanton, which connects the reactant and product valleys of the potential energy surface.…”