Extensive Theoretical Study of the Thermochemical Properties of Unsaturated Hydrocarbons and Allylic and Super-Allylic Radicals: The Development and Optimization of Group Additivity Values

In this study, the thermochemistry of C2–C7 unsaturated hydrocarbons (22 alkene and 6 diene molecules) and 16 allylic and 5 super-allylic radicals is determined using high-accuracy quantum chemistry calculations. In addition, the group additivity values (GAVs) of a total of 19 relevant groups are systematically optimized on the basis of the calculated thermochemistry of species clusters. The M06-2X method using the 6-311++G(d,p) basis set is used for the geometry optimizations, vibrational frequency calculations, and internal rotation scans for lower-frequency modes. The composite compound methods, CBS-APNO, G3, and G4, are utilized to derive the average atomization formation enthalpies. The entropy and temperature-dependent heat capacity values of all species are calculated using statistical thermodynamics in MultiWell. These results are in good agreement with literature data. A GAVs optimization is performed on the basis of a statistical analysis: a Bland–Altman plot, which is employed to visualize the ...