DFT studies toward the design and properties of high-energy density hydrocarbon fuel

Pentacyclo[5.4.0.02,6.03,10.05,9]undecane (PCU) and its hydrocarbon derivatives have been widely investigated due to their inherent energetic advantages as hydrocarbon fuels. Based on the optimized molecular geometries at the B3LYP/6-31G∗∗ level, geometric structures, heats of formation, densities, IR spectra, thermodynamic functions, as well as 13C and 1H NMR chemical shifts, were obtained and discussed for all possible singly methylated, ethylated, isopropylated, and isobutylated PCUs and four PCU alkene dimers. The comparisons of the calculated densities, thermodynamic functions and NMR chemical shifts show good agreements with the available experimental results, which imply the reliability of the present method. The influences of the position and size of substitution alkyl groups on HOFs and densities are discussed, and the magnitudes of the calculated HOFs and densities indicate that the studied PCU derivatives are promising high-energy density hydrocarbon fuels. IR regions, 13C and 1H NMR chemical shifts are assigned and discussed. In addition, the relationships of the thermodynamic functions with temperature and the substitution group are also investigated, and it is found that the latter shows a good group additivity rule.