The Elusive Formaldonitrone, CH2N(H)O. Preparation in the Gas Phase and Characterization by Variable-Time Neutralization−Reionization Mass Spectrometry, and Ab Initio and Density Functional Theory Calculations

Abstract

Formaldonitrone, CH2N(H)O (1), the hitherto elusive simplest organic nitrone, has been prepared transiently in the gas phase by femtosecond collisional neutralization of its cation radical, CH2N(H)O+• (1+•). Ion 1+• was generated by dissociative ionization of 1,2-oxazolidine and characterized by collisionally activated dissociation mass spectra and augmented Gaussian 2(MP2) calculations. Nitrone 1 showed negligible dissociation upon collisional neutralization and was distinguished from its tautomers formaldoxime (2) and nitrosomethane (3). 1 was calculated to be more stable than its isomers CH2−O−NH (5) and oxaziridine (6). The enthalpy of formation of 1 was calculated from enthalpies of atomization and two isodesmic reactions as ΔHf,298(1) = 58 ± 1 kJ mol-1. The adiabatic and vertical ionization energies of 1 were calculated as IEa = 9.40 eV and IEv = 9.42 eV, the vertical recombination energy of 1+• was REv = 9.35 eV. Formation of 1 by collisional electron transfer was accompanied by negligible Franck−Condon effects. The potential energy surfaces for the formation, isomerizations, and dissociations of 1 and 1+• were investigated by ab initio calculations.