Truncamento das funções de partição rovibracionais multiestruturais e seus efeitos na estimativa de constantes de velocidade térmica.

Abstract

Thermal rate constants for the hydrogen abstraction reaction of methyl pentanoate were calculated using the multistructural canonical variational theory state theory with small curvature tunneling. The conformational searches for the stationary points generated by these reactions were performed with an algorithm that combines systematic and stochastic searches in dual-level. At the high-level theory, MPWB1K/6-31+G(d,p), 23 conformers were found for the methyl pentanoate. The transition states of R1-R5 ranged from 27 to 64 structures. A systematic evaluation of the truncation of the rovibrational partition functions and their effects on thermal rate constants was carried out. Our results indicate that the truncation of the partition functions in a small set of conformations generates deviations in the rate coefficients ranging from 20 to 60%, compared to estimates of the rate coefficients with the consideration of all the structures of reagents and transition states. It is expected that the reliability and perspective of this master’s thesis will motivate and guide future investigations on reactions involving long-chain methyl esters with low computational costs.