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 <CH3O(C)over bar HCN> and <CH3S(C)over bar HCN> carbanions into a methyl radical and the radical anion of formyl cyanide and thioformyl cyanide, respectively (BDE(<CH3O(C)over bar HCN>) = 116 +/- 10 kJ mol(-1) and BDE(<CH3S(C)over bar HCN>) = 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.