Jose Luis M. Abboud

Neutral, ion gas-phase energetics and structural properties of hydroxybenzophenones.

We have carried out a study of the energetics, structural, and physical properties of o-, m-, and p-hydroxybenzophenone neutral molecules, C(13)H(10)O(2), and their corresponding anions. In particular, the standard enthalpies of formation in the gas phase at 298.15 K for all of these species were determined. A reliable experimental estimation of the enthalpy associated with intramolecular hydrogen bonding in chelated species was experimentally obtained. The gas-phase acidities (GA) of benzophenones, substituted phenols, and several aliphatic alcohols are compared with the corresponding aqueous acidities (pK(a)), covering a range of 278 kJ.mol(-1) in GA and 11.4 in pK(a). A computational study of the various species shed light on structural effects and further confirmed the self-consistency of the experimental results.

Nitro derivatives of pyrrole, furan and 1H-tetrazole: ring or nitro bases?

The gas-phase basicity of pyrrole, furan, 1H-tetrazole and their nitro derivatives has been analyzed by means of high level ab initio and DFT calculations. The gas-phase basicity of 2-nitrofuran was also determined by means of FT-ICR mass spectrometry. Our results indicate that although pyrrole and furan behave as carbon bases in the gas phase, their nitro derivatives protonate preferentially on the nitro group. Conversely, both 1H-tetrazole and its 5-nitro derivative protonate preferentially on the ring, because the intrinsic basicity of the nitro group is significantly dampened when the group is attached to a tetrazolic ring. For the 5-nitro-1H-tetrazole the most stable protonated species corresponds to an open structure formed by protonation on N1, which is followed by a N1–N2 bond cleavage. This non-cyclic structure is entropically favored and therefore it should be the one observed in ICR measurements.

Ab initio study on the thermolysis of β-hydroxyolefins in gas phase

Abstract Thermolysis studies of β-hydroxyolefins in gas phase were realized using ab initio MP2 and DFT methods at the 6-31G∗ levels to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state (TS). Vibrational frequency calculations were carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. With the aim of corroborating the postulated mechanism in the experimental study, we present a theoretical study in order to calculate the rate constants and the activation parameters. The results obtained are in accordance with the experimental conclusions.