Thermochemistry and dissociation dynamics of state-selected C4H8O2+ ions. 2. Butanoic acid

Abstract

more stable structure even though at least four such ionic structures (ethyl acetate and its enol, and butanoic acid and its enol) are more stable. In addition, dioxane(+) does not produce fragment ions and neutrals in their most stable configuration. Instead, products which can be formed by simple bond cleavages from dioxane tend to be formed.The RRKM/QET calculated dissociation rates agree extremely well with measured decay rates of internal energy selected metastable dioxane ions. From these data as well as kinetic energy release results for the C3H60+ + CH20 production we conclude that the ion formed has the CH2-0-CH2CH2 structure and has a AHf°298 = 828 ± 8 kJ/mol. This compares very well with an ab initio calculated energy of 833 ± 17 kJ/mol.25 The RRKM/QET calculations also suggest that the transition states, par-ticularly for the m/e 44 and 45 production, are very tight. That is, the transition state structure is a highly strained one.Acknowledgment. Tomas Baer acknowledges his sincere gratitude to Simon Bauer for providing an exciting and stimulating atmosphere during his 4 years at Cornell. Si's enthusiasm for the new and the unexpected were then, and still are now, a constant source of inspiration. We are grateful to the National Science Foundation for the support of a portion of this work. The structure and energetic studies were supported by the Department of Energy.

Decompositions of ionized isopropyl methyl ether: complex-mediated and direct processes in unimolecular dissociations

“…A discrepancy between observed and calculated decomposition rates of ionized methane has been removed by including the effects of tunneling in the calculation 42 A similar difference between calculated and observed rates for the butanoic acid ion has been attributed to isomerization to lower energy, longer lived intermediates. 43 Finally, observations similar to the ones we report here for ion-permanent dipole complexes have been attributed to a very high density of states in the reactant due to lowering of the vibrational frequency of the ion-dipole bond as it elongates.44 None of these explanations seems applicable here. A similar mismatch between observed and calculated lifetimes has been encountered by Rosenstock and co-workers in the decomposition of 2-bromopropane ions.…”

Tracking the reaction networks of acetaldehyde oxide and glyoxal oxide Criegee intermediates in the ozone-assisted oxidation reaction of crotonaldehyde

“…The ionization threshold of the C4H8O2 signal measured in this experiment at a reaction temperature of 390 K is observed around 9.50 ± 0.05 eV (see Figure 10 10.20 ± 0.05 eV matches the ionization energy of 10.17 eV reported in the literature for butanoic acid. 98 Interesting enough, the PIE curve measured in our experiment resembles the characteristics of the PIE curve reported by Zhai et al 99 for the C4H8O2 signal, which was attributed to the contribution of but-1-enyl-3-hydroperoxide, but-2-enyl-1-hydroperoxide, and butanoic acid.…”

Carbocation-like isomerisations at radical sites precede methyl losses from ionised butanoic acid

“…-(8) are strongly preferred to those paralleling (4) -+ (3)." The differences could be due to a higher activation energy for (2) -(8) than for the corresponding C4H80+' and C5H oO + ' isomerisations.…”