The imidic acids HNC(H)OH and CH 3NC(H)OH and their tautomeric carbenes H 2N7z.sbnd;C̈OH and CH 3N(H)C̈OH: stable species in the gas phase formed by one-electron reduction of their cations

Abstract

The prototype imidic acid, formimidic acid, HNC(H)OH, 2, as well as aminohydroxy-carbene, 3, both isomeric with formamide, 1, have been generated in the gas phase by one-electron reduction of the corresponding radical cations. The ionic precursors 2 + and 3 + were produced by appropriate dissociative ionizations, whereas 1 + was formed by direct ionization of formamide. From a detailed analysis of collision induced dissociation (CID) mass spectra, in particular MS/MS/MS data from D- and 15N-labelled isotopomers, it was possible to assign structures to ions 1 + , 2 + and 3 + and to ascertain that, for each, ion beams could be obtained which were free from the other two isomers. Reduction of these ions in neutralization-reionization experiments produced intense “survivor” signals. By combining the information contained in CID mass spectra of the “survivor” ions with that from labelling experiments, the existence of 2 and 3 as stable molecules in the gas phase could be established. Among the vibrationally excited molecules we find evidence for the simplest amide-iminol tautomerism, i.e. 1 ↔ 2 (a reaction which because of the high barrier is not observed in solution). At higher internal energies decarbonylation occurs. The experimental findings on ions and neutrals 1-3 concur with previously published ab initio MO studies which were supplemented by our own results at the UMP3/6-31G *//4-31G (+ZPVE) level of theory. Using the same experimental methodology, the existence of the imidic acid CH 3NC(H)OH and the carbene CH 3N(H)C̈OH, the methyl homologues of 2 and 3, was also established.