Knowledge of a Molecule: An Experimental and Theoretical Study of the Structure and Enthalpy of Formation of Tetrahydro-2H-1,3-oxazine-2-thione

In a continuation of our investigations of the thermochemistry of heterocyclic ring systems and sulfur-containing compounds, the standard molar enthalpy of formation of tetrahydro-2 H -1,3-oxazine-2-thione (CAS no. 17374-18-4) at  T  = 298 K has been evaluated both experimentally and computationally. Combined enthalpies of combustion and sublimation, measured by rotary bomb combustion calorimetry and the Knudsen effusion technique, yielded a gas-phase enthalpy of formation of −(104.0 ± 5.5) kJ·mol –1 . The G3 value of −104.6 kJ·mol –1  calculated using an isodesmic bond separation reaction is in excellent agreement with the experimental result. The variation in enthalpy of formation with ring size is discussed, and the G3 enthalpy of formation of tetrahydro-2 H -1,3-thiazine-2-thione (72.4 kJ·mol –1 ) was also computed for this purpose.