STANDARD ENTHALPIES OF FORMATION OF 2-THENOYLTRIFLUOROACETONE AND MONOTHIO-2-THENOYLTRIFLUORO ACETONE BY ROTATING-BOMB CALORIMETRY

The standard (p degrees = 0.1 MPa) molar enthalpies of formation of cr ystalline 1-trifluoro-4-(2-thienyl)-4-hydroxy-3-buten-2-one, HTTFA, an d -trifluoro-4-(2-thienyl)-4-mercapto-3-buten-2-one, HTTFAS, at T = 29 8.15 K were measured by rotating-bomb calorimetry and the standard mol ar enthalpies of sublimation at T = 298.15 K were measured by microcal orimetry, with the following results: [GRAPHICS] The results demonstra te an increase in stabilization energy of approximate to (38.7 +/- 5.0 ) kJ.mol(-1) in HTTFA compared with thiophene and that in these molecu les, the intramolecular hydrogen bond energy (O-H...O), appears approx imate to 20 kJ.mol(-1) larger than for (S-H...O). (C) 1997 Academic Pr ess Limited.