The standard (pdegrees = 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. [GRAPHIC] 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). (C) 2004 Elsevier Ltd. All rights reserved.