This work was undertaken to obtain new thermochemical data for 5-hydroxymethylfurfural (HMF) and parent Compounds. The standard molar enthalpy of formation in the gaseous state of HMF was obtained from combustion calorimetry, differential scanning calorimetry (DSC), and measurements of the temperature dependence of the vapor pressure by the transpiration method. To verify the experimental data, ab initio calculations of all compounds were performed. Enthalpies of formation derived from the G3MP2 method are in an excellent agreement with the experimental results. A weak hydrogen bond in HMF was revealed using ab initio methods. Thermodynamic analysis of the transformation of HMF to the bulk intermediates according to hydrogenation and oxidation pathways has revealed a very high feasibility of these reactions, with equilibrium constants that are completely shifted to the desired reaction products even at 298 K.