Revisiting protomers of aniline by high-resolution ion mobility spectrometry, capillary electrophoresis-mass spectrometry, and abinitio calculations

The detection of two stable tautomers of protonated aniline, the amino-protonated and the protonated carbone in para position (“Cpara-protonated”), are already reported in the literature. The use of traveling wave ion mobility spectrometry (TWIMS) spotlights a possible conversion between both of these tautomers. Moreover, the presence of phenol strongly suggests that water adduct(s) is/are involved during this tautomerisation. The use of high resolution ion mobility - mass spectrometry also suggests tautomers conversion and the presence of other metastable species of protonated aniline than the Cpara-protonated and amino-protonated aniline. These observations support that the measurement of protomers ratio should be affect by gas phase reactions. Aqueous and non-aqueous capillary electrophoresis results show the effect of the solvents. The rate of tautomers conversion seems to be higher in protic solvent (water) than aprotic solvent (acetonitrile).