Enthalpies of Formation and Bond Dissociation Energies of Lower Alkyl Hydroperoxides and Related Hydroperoxy and Alkoxy Radicals

Abstract

The enthalpies of formation and bond dissociation energies, D (ROO-H)and D(R-OOH) of alkyl hydroperoxides, ROOH, alkyl peroxy, RO, and alkoxide radicals, RȮ , have been computed at CBS-QB3 and APNO levels of theory via isodesmic and atomization procedures for R ) methyl, ethyl, n-propyl and isopropyl and n-butyl, tert-butyl, isobutyl and sec-butyl. We show that D(ROO-H) ≈ 357, D(RO-OH) ≈ 190 and D(RO-Ȯ ) ≈ 263 kJ mol -1 for all R, whereas both D(R-Ȯ O) and D(R-OOH)strengthen with increasing methyl substitution at the R-carbon but remain constant with increasing carbon chain length. We recommend a new set of group additivity contributions for the estimation of enthalpies of formation and bond energies.

Structural and heat of formation studies of halogenated methyl hydro-peroxides

“…Chlorination also increases the CH 2 Cl-OOH bond dissociation energy compared to CH 3 -OOH but the presence of additional chlorine [18] and bromine atoms leads to declining BDE(R-OOH) values, assumingly due to the weaker induction effect of Cl and Br compared to F. The effect of I atoms is interesting since it leads to significantly larger BDE(R-OOH) results although introduction of the second I atom does have a decreasing effect. Apparently, the influence of the iodine in the methyl group because of its lower electronegativity, rather resembles the effect of the increasing chain and branching of the alkyl fragment [22] than the halogen induction effect. Indeed, EtOOH and iPrOOH have been found to present increasing BDE(R-OOH) values compared to Me-OOH [22].…”

“…Knowledge of their structure and thermodynamics is useful for studying the mechanism of the oxidation pathways in the chemistry of combustion and flames, in atmospheric chemistry and in various biochemical oxidizing processes. Hence, several experimental and theoretical investigations have been carried out to examine and characterize the geometrical, spectroscopic and thermochemical properties of simple and halogenated alkyl hydro-peroxides [10][11][12][13][14][15][16][17][18][19][20][21][22].…”

“…Focus in several reports has been given on changing the size and the branching of the alkyl group along the sequence R = methyl, ethyl, isopropyl, tert-butyl, isobutyl and sec-butyl [22] in order to determine the effect of increased aliphatic chain and branching on bond energies and thermodynamic stability. Less attention has been given to examine the induction effect of halogen substitution in the alkyl group.…”

Modeling Combustion with Detailed Kinetic Mechanisms

“…For example, studies have been made for n-alkanes (Vansteenkiste et al 2003) or a wide rage oxygenated molecules or radicals (Sumathi and Green 2002;Sebbar et al 2004Sebbar et al , 2005Da Silva and Bozzelli 2006;Simmie et al 2008;Yu et al 2006).…”

Comparação entre métodos compostos no cálculo de afinidades por próton e elétron em sistemas moleculares

“…[32][33][34][35][36][37][38][39][40][41][42][43][44] Outra aplicação interessante é no estudo do mecanismo em processos envolvidos em espectroscopia de massas. 45 A variedade de aplicações utilizando métodos compostos vem aumentando tanto em trabalhos teóricos como em trabalhos experimentais, devido à sua praticidade, confiabilidade e precisão em prever parâmetros físico-químicos.…”