Rate Constant Dependence on the Size of Aldehydes in the NO₃ + Aldehydes Reaction. An Explanation via Quantum Chemical Calculations and CTST

Abstract

The reactions of NO(3) with formaldehyde, acetaldehyde, propanal, n-butanal, and isobutanal have been modeled using accurate ab initio and hybrid DFT methods with large basis sets. The results clearly indicate that the reaction is a simple aldehydic H atom abstraction; no adduct was found to support the idea of a complex mechanism. Alternative hydrogen abstractions were modeled for the alpha carbon hydrogen atoms and for the Cbeta of n-butanal; the differences in activation energies ruled out the possibility that competitive abstraction could be responsible for the anomalous increase of the rate constants with the size of aldehydes. The anomalous behavior was found to be a consequence of the preexponential factor increase, due to the enlargement of the internal rotation partition functions with the size of the aldehydes. The reaction rate constants, calculated using the conventional transition-state theory as applied to a proposed simple mechanism, reproduce remarkably well the reported experimental results. Consideration of the internal rotation partition functions is shown to be essential for the determination of the preexponential parameters and thus for the correct calculation of the rate constants. The tunneling correction was found negligible due to the features of the transition vector.

Computational determination of fundamental pathway and activation barriers for acetohydroxyacid synthase‐catalyzed condensation reactions of α‐keto acids

“…The calculated activation barrier increase of 1.7 kcal/mol is in good agreement with the experimental observation that the Glu47Ala mutation on E. coli AHAS II (corresponding to Glu144Ala mutation on A. thaliana AHAS II) decreased the catalytic rate constant (k cat ) of the enzyme by $13-fold, 42 as a $13-fold decrease in k cat corresponds to a $1.5 kcal/mol increase in activation barrier according to the conventional transition state theory (CTST). 55,56 It should be pointed out that the starting structures used for the above QM/MM reaction coordinate calculations were all based on the X-ray crystal structure. Warshel and coworkers 57 noted that QM/MM reaction coordinate calculations on an enzymatic reaction system using different starting structures could lead to significantly different activation barrier values.…”

Kinetics of the gas‐phase reaction of n‐C6–C10 aldehydes with the nitrate radical

“…Quantum chemical calculations were used by Alvarez-Idaboy et al [24] and by Mora-Diez and Boyd [25] to give insight into the reaction mechanism. Application of classical transition state theory then provided kinetic parameters.…”

“…Application of classical transition state theory then provided kinetic parameters. Mora-Diez and Boyd [25] made calculations for formaldehyde, some halogenated formaldehydes, and for acetaldehyde, while AlvarezIdaboy et al [24] treated the series formaldehyde to butanal. In both cases, the calculations were taken to a level of refinement where the results well reproduce experimental data.…”

“…In summary, both groups were able to carry out successful calculations using a simple elementary abstraction step without invoking an addition complex in the mechanism. With reference to conventional transition state theory, Alvarez-Idaboy et al [24] found that the unusual behavior of the aldehyde-nitrate radical rate coefficients is mainly caused by the frequency factor of the rate coefficient expression and not by the exponential, activation energy-dependent part. The frequency factor is a function of the partition functions ratio, which in turn depends, e.g., on the internal rotation partition function of the transition state.…”

Theoretical investigation on the role of mineral dust aerosol in atmospheric reaction: A case of the heterogeneous reaction of formaldehyde with NO 2 onto SiO 2 dust surface

“…Due to the potential adverse effects on human health and the active involvement in the atmospheric reactions (Ji et al, 2012), the atmospheric reactions of VOCs have attracted significant scientific and regulatory attention. Therefore, the homogeneous atmospheric reactions of VOCs with various reactive species (RSs) have been investigated in detail currently, and significant advances were made to understand both the kinetics and mechanisms of these reactions, as well as their global impact on the atmosphere (Alvarez-Idaboy et al, 2001;Atkinson, 2000;Atkinson and Arey, 2003;Stemmler et al, 1997). Recently, a few laboratory studies attempted to investigate the heterogeneous reactions of simple VOCs onto the mineral dusts, and the strong interactions can be found between the mineral particles and VOCs in addition the significant influence of mineral dusts onto the atmosphere (McNaughton et al, 2009;Zhao et al, 2011Zhao et al, , 2010.…”