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[摘要]：High-level ab initio calculations have been performed on the exo and endo isomers of gas-phase tetra-hydrodicyclopentadiene (THDCPD), a principal component of the jet fuel JP10. using the Gaussian G(x) and G(x)(MPx) composite methods, as well as the CBS-QB3 method, and using a variety of isodesmic and homodesmotic reaction schemes. The impetus for this work is to help resolve large discrepancies existing between literature measurements of the formation enthalpy Delta H-f degrees(298) for exo-TDCPD. We find that use of the isodesmic bond separation reaction C10H16 + 14CH(4) -> 12C(2)H(6) yields results for the era isomer (JP10) in between the two experimentally accepted values, for the composite methods G3(MP2), G3(MP2)//B3LYP, and CBS-QB3. Application of this same isodesmic bond separation scheme to gas-phase adamantane yields a value for Delta H-f degrees(298) within 5 kJ/mol of experiment. isodesmic bond separation calculations for the endo isomer give a heat of formation in excellent agreement with the experimental measurement. Combining our calculated values for the gas-phase heat of formation with recent measurements of the heat of vaporization yields recommended values for Delta H-f degrees(298)liq of -126.4 and -114.7 kJ/mol for the exo and endo isomers, respectively. |
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