Experimental Determination of the Enthalpies of Formation of Formyl Cyanide and Thioformyl Cyanide in the Gas Phase

Abstract

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, ∆H f°( 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 CH 3 OCH 2 CN and CH 3 SCH 2 CN species (∆H°a cid (CH 3 OCH 2 CN) ) 1556 ( 8 kJ mol -1 and ∆H°a cid (CH 3 SCH 2 CN) ) 1494 ( 8 kJ mol -1 ), (ii) the enthalpy change for the dissociation of the CH 3 OC h HCN and CH 3 SC h HCN carbanions into a methyl radical and the radical anion of formyl cyanide and thioformyl cyanide, respectively (BDE-(CH 3 OC h HCN) ) 116 ( 10 kJ mol -1 and BDE(CH 3 SC h 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.

The role of conjugative interactions in acidic and basic character of five membered aromatic heterocyclics

“…The comparisons of the PA values at B3LYP/6-311++G**//B3LYP/6-31+G*, MP2/6-31++G**// MP2/6-31+G* with G2MP2 values and there experimental results indicate that DFT method are more appropriate. The available experimental values are also included in Table 1 [25,[36][37][38].…”

The proton affinities of saturated and unsaturated heterocyclic molecules

“…A Fourier Transform Ion Cyclotron Resonance Bruker Daltonics Apex II instrument was used to determine the experimental proton affinities as described previously [31]. The total pressure in the instrument was in most experiments (1-3) × 10 −6 Pa as measured with an ionization gauge placed in a side arm of the main vacuum system.…”

Protonation of fluorophenols and fluoroanisoles in the gas phase: experiment and theory

“…( 5) if the temperature of the reactant chemical system in the FT-ICR instrument is assumed to be 298 K (Table 2). 37,43 The change in Gibbs energy for the equilibrium reaction (eqn. ( 4)) is according to the definition of the gas-phase basicity GB (ÀD r G o (298 K) for the reaction in eqn.…”