Structural effects on the thermochemical properties of cycloalkanones. III. Enthalpy of combustion, vapour pressures, and enthalpy of sublimation, and standard enthalpy of formation in the gaseous phase of pentacyclo-[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione

The standard molar energy of combustion of pentacyclo[5.4.0.0(2,6).0(3,10). 0(5,9)]undecane- 8,11-dione has been determined by using a static bomb calo rimeter. The vapour pressure of the compound was measured in the interval T = 325.64 K to T = 340.97 K by the Knudsen-effusion technique. Enthalpy of fusion and enthalpy of transition measurements were carried out by differen tial scanning calorimetry (d.s.c.). From the experimental results of this w ork, the standard enthalpies of combustion, sublimation, and formation in t he crystalline and gaseous state at the temperature 298.15 K have been deri ved for pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione: Delta(f )H(m)(o) (cr) = -(206.2 +/- 3.2) kJ.mol(-1), Delta(sub)H(m)(o) = (92.6+/-1) kJ.mol(-1), Delta(f)H(m)(o) (g) = -(113.6 +/- 3.4) kJ.mol(-1). Strain ener gy due to the presence of the two carbonyl groups in the molecule is estima ted by three different methods with consistent results. (C) 1999 Academic P ress.