Experimental and computational study on the energetics of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene (dibenzosuberane)

A study on the molecular structure and energetics of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene (dibenzosuberane) was performed combining experimental calorimetric techniques and high level computational calculations. In the experimental work, the solid phase standard (p0 = 0.1 MPa) molar enthalpy of formation of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene was derived from its standard massic energy of combustion, at T = 298.15 K, measured by static bomb combustion calorimetry, in oxygen. The respective standard molar enthalpy of sublimation, at T = 298.15 K, was measured by Calvet microcalorimetry enabling the calculation of the standard molar enthalpy of formation (161.4 ± 3.7) kJ · mol-1, in the gaseous phase, at T = 298.15 K. In addition, computational calculations were performed using the density functional theory with the B3LYP hybrid functional and extended basis sets in order to obtain the molecular structure of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene and that of related molecules. Estimates of the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, for 10,11-dihydro-5H-dibenzo[a,d]cycloheptene were performed using three different methods: G3(MP2)//B3LYP, MC3BB, and MC3MPW and appropriate homodesmic reactions. Computational estimates are in very good agreement with the experimental value.