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4‐Nitropyrazole: a nitrogen or an oxygen base in the gas phase?

1999; Wiley; Volume: 12; Issue: 10 Linguagem: Inglês

10.1002/(sici)1099-1395(199910)12

1099-1395

José‐Luis M. Abboud, Rafael Notario, Manuel Yáñez, Otília Mó, Robert Flammang, Nadine Jagerovic, Ibón Alkorta, José Elguero,

Chemical Thermodynamics and Molecular Structure

Protonated 3- and 4-nitropyrazoles were subject to collisional activation and neutralization–reionization mass spectrometric studies using a large scale tandem mass spectrometer. The gas phase basicities of 2- and 4-nitroimidazoles were determined by means of Fourier transform ion cyclotron resonance spectroscopy. These and other neutral and protonated molecules were studied by ab initio methods up to and including the CCSD(T)/6–31 + G* level. This information was used to assess the site of protonation of 3-nitro- and 4-nitropyrazole in the gas phase: at the equilibrium these compounds protonate on the heterocyclic nitrogen rather than on the oxygen of the nitro group. Copyright © 1999 John Wiley & Sons, Ltd.