Journal of Physical Chemistry, Vol.100, No.44, 17662-17669, 1996
Experimental-Determination of the Enthalpies of Formation of Formyl Cyanide and Thioformyl Cyanide in the Gas-Phase
The enthalpies of formation of formyl cyanide (HC(O)CN) and thioformyl cyanide (HC(S)CN) in the gas phase have been determined with the use of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, The enthalpy of formation, Delta H-f degrees(298 K), of formyl cyanide is determined to be 26 +/- 20 kJ mol(-1), whereas the value for thioformyl cyanide is 222 +/- 30 kJ mol(-1). These enthalpies of formation are derived from experimental values of (i) the gas-phase acidities of the methylene groups in the CH3OCH2CN and CH3SCH2CN species (Delta H(acid)degrees(CH3OCH2CN) = 1556 +/- 8 kJ mol(-1) and Delta H(acid)degrees(CH3SCH2CN) = 1494 +/- 8 kJ mol(-1)), (ii) the enthalpy change for the dissociation of the and carbanions into a methyl radical and the radical anion of formyl cyanide and thioformyl cyanide, respectively (BDE() = 116 +/- 10 kJ mol(-1) and BDE() = 133 +/- 10 kJ mol(-1)), and (iii) the electron affinities of the neutral formyl species (EA(HC(O)CN) = 65 +/- 3 kJ mol(-1) and EA(HC(S)CN) = 159 +/- 15 kJ mol(-1)), The structures of the two carbanions and the radical anions of the (thio)formyl species have been ascertained by high kinetic energy (8 keV) collision-induced charge-reversal (CR) experiments performed with the use of a double-focusing quadrupole hybrid mass spectrometer.
Keywords:TRANSLATIONAL ENERGY-DEPENDENCE;COLLISION-INDUCED DISSOCIATION;PYROLYSIS JET SPECTROSCOPY;MASS-SPECTROMETRY;FOURIER-TRANSFORM;ELECTRON-AFFINITIES;NEGATIVE-IONS;METHANE;HEATS;STABILIZATION