Determination of thermodynamic parameters of tautomerization in gas phase by mass spectrometry and DFT calculations: Keto-enol versus nitrile–ketenimine equilibria

Experimental Study of Tautomeric Equilibria of 2-Cyanobenzoic Acids in Gas, Solution and Solid Phase

“…Besides, for GC/MS (Gas Chromatography/Mass Spectrometry) experiments, once the solvent is separated after injection in the injection port of the gas chromatograph, tautomerism mechanisms (intermolecular or unimolecular) would not seem to take place even without chromatographic separation of the tautomers (under the selected experimental conditions). These conclusions are supported by temperature studies at the ion source (negligible effect) and at the injection port of the gas chromatograph (shifts of the relative abundances of tautomer-specific ions are in agreement with the corresponding heats of tautomerization) [4,[8][9][10]. In fact, tautomerism would take place very fast in the injection port of the GC under the working conditions.…”

“…It has been demonstrated in the case of keto-enol tautomerism of a variety of carbonyl and thiocarbonyl compounds [4][5][6][7][8][9][10] that there is no significant interconversion of the tautomeric forms in the gas phase following electron impact ionization in the ion source of the mass spectrometer prior to fragmentation (molecular ions, M +. , do not seem to undergo *Address corresponding to this author at the Laboratorio de Estudio de Compuestos Orgánicos (Laboratorio LADECOR), Departamento de Química, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, Calle 47 y 115, B1900 La Plata, Pcia.…”

“…Separation of tautomers in analytical columns is usually very difficult, even when it has been carried out successfully for some compounds (previous work has reported chromatographic separation of the tautomeric forms for -ketoesters [11]). Consequently, the different pathways of fragmentation of the tautomeric forms have to be used for identification of individual tautomers [4,[8][9][10]. For this reason and because of the high similarity between MS (commercial databases) and GC/MS spectra (the GC separation would not contribute to the complex distribution of internal energies of the ions formed in the ion source), the analytical separation has not been considered critical for the present work.…”

Solvent effect in keto–enol tautomerism for a polymerizable β-ketonitrile monomer. Spectroscopy and theoretical study

“…Among these, DFT has proven to be very effective. Keto-enol and nitrile-ketenimine equilibria of the analyzed compound in the present work, were previously studied by mass spectrometry [10]. A good correlation was found in enthalpy changes obtained experimentally and by density functional theory (DFT) calculations, in which the ketonitrile tautomer was favoured.…”

“…The existence of all these tautomeric forms in the gas phase has been previously demonstrated by CG-MS [10]. The nitrile-ketenimine equilibrium could not be observed by 1 H NMR spectrometry, due to the lower sensitivity of this method and the low proportion of keto-ketenimine form (see Correlation with theoretical calculations section) [32].…”