Competition between Reaction and Intramolecular Energy Redistribution in Solution: Observation and Nature of Nonstatistical Dynamics in the Ozonolysis of Vinyl Ethers

Abstract

Experimental product ratios in ozonolyses of alkyl vinyl ethers in solution do not fit with expectations from statistical rate theories. The selectivity among cleavage pathways increases with the size of the alkyl group but to an extent that is far less than RRKM theory would predict. Trajectory studies account for the observed selectivities and support a mechanism involving a competition between cleavage of the primary ozonide and intramolecular vibrational energy redistribution. An approximate statistical model is presented that assumes that RRKM theory holds for a molecular subset of the primary ozonides, allowing estimates of the rates of energy loss from the primary ozonides based on the observed product ratios.

The Study of Reactive Intermediates in Condensed Phases

“…Even when the branching of reaction paths does occur at a local PES minimum, classical molecular dynamics (MD) simulations have shown that one cannot rely on the validity of the statistical approximation for gas-phase reactions. 15,16,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] The Figure 1. Schematic depiction of a PES with a bifurcating reaction path.…”

“…The first study involved ozonolyses of vinyl ethers with alkane side-chains of varying length. 31 The results have been reviewed in detail elsewhere, 123 and so will be summarized only briefly here. In short, Singleton's group measured product ratios for the ozonolysis of compounds of the class RO-CH=CH2 in CD3OD solution.…”

How Frustrated Lewis Acid/Base Systems Pass through Transition‐State Regions: H2 Cleavage by [tBu3P/B(C6F5)3]

“…In a number of cases the TST/MEP approach has been shown to fail, althougha consensus about origins of dynamical effects is yet to be reached. [9] Notable examples of nonstatistical dynamics in chemical reaction mechanisms include: an intramolecular rearrangement with the dynamics-driven reaction pathways, [10] "hot" intermediates and dynamics of alkene hydroboration, [11] roaming chemical reactions, [12][13][14] the dynamics of S N 2 nucleophilic substitution in the gas phase, [15][16][17] the involvement of protein dynamics in enzyme catalysis, [18,19] and the post-TS bifurcation(s) of the reaction path, [20][21][22] to name only a few. Owing to the remarkable progress that has been achieved in both experimental and theoretical methodologies over the last few decades, especially in respect to femtochemistry, molecular collisions techniques, and efficient ab initio molecular dynamics implementations applicable to massively polyatomic systems, it is now possible to probe the femtosecond dynamics of chemical transformations to acquire information on the chemical activity of real molecules without overreliance on TST/MEP.…”

Theoretical and computational studies of non-equilibrium and non-statistical dynamics in the gas phase, in the condensed phase and at interfaces

“…This is exactly why the solvent relaxation time is involved in determining the actual trajectory that a reactive path follows. Recently, some post-TS dynamics was performed in the liquid phase, pointing out the appearance of dynamical effects [63][64][65][66][67]…”