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

✍ Scribed by José-Luis M. Abboud; Rafael Notario; Manuel Yáñez; Otilia Mó; Robert Flammang; Nadine Jagerovic; Ibon Alkorta; José Elguero

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 109 KB
• Volume: 12
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199910)12:10<787::aid-poc199>3.0.co;2-e

✦ Synopsis

Protonated 3-and 4-nitropyrazoles were subject to collisional activation and neutralizationreionization mass spectrometric studies using a large scale tandem mass spectrometer. The gas phase basicities of 2and 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.