Abstract The standard (p∘=0.1 MPa) molar enthalpies of formation of crystalline thianthrene and monothiodibenzoylmethane, HDBMS, at T=298.15 K were measured by rotating-bomb calorimetry and the standard molar enthalpies of sublimation at T=298.15 K of dibenzoylmethane (HDBMO) and monothiodibenzoylmethane (HDBMS) were measured by microcalorimetry. Δ c U m ∘ (cr)/(kJ · mol−1) Δ f H m ∘ (cr)/(kJ · mol−1) Δ cr g H m ∘ /(kJ · mol−1) Thianthrene – 7239.1 ± 2.5 182.1 ± 3.1 HDBMS – 8203.7 ± 2.0 – 6.0 ± 2.8 125.5 ± 4.9 HDBMO 113.3 ± 4.8 From the present results it could be shown that, in these molecules, the intramolecular hydrogen bond energy (O–H⋯O), is ca. 20 kJ · mol−1 larger than for (S–H⋯O).