THE IMIDIC ACIDS H-N=C(H)-OH AND CH3-N=C(H)-OH AND THEIR TAUTOMERIC CARBENES H2NC-OH AND CH3-N(H)-C-OH - STABLE SPECIES IN THE GAS-PHASE FORMED BY ONE-ELECTRON REDUCTION OF THEIR CATIONS

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 g enerated in the gas phase by one-electron reduction of the correspondi ng 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 f rom D- and N-15-labelled isotopomers, it was possible to assign struct ures to ions 1(.+) 2(.+) and 3(.+) and to ascertain that, for each, io n beams could be obtained which were free from the other two isomers. Reduction of these ions in neutralization-reionization experiments pro duced intense ''survivor'' signals. By combining the information conta ined in CID mass spectra of the ''survivor'' ions with that from label ling experiments, the existence of 2 and 3 as stable molecules in the gas phase could be established. Among the vibrationally excited molecu les we find evidence for the simplest amide-iminol tautomerism, i.e. 1 <-> 2 (a reaction which because of the high barrier is not observed i n solution). At higher internal energies decarbonylation occurs. The e xperimental findings on ions and neutrals 1-3 concur with previously p ublished ab initio MO studies which were supplemented by our own resul ts at the UMP3/6-31G//4-31G (+ZPVE) level of theory. Using the same e xperimental methodology, the existence of the imidic acid CH3-N=C(H)-O H and the carbene CH3-N(H)-C-OH, the methyl homologues of 2 and 3, was also established.