THERMOCHEMICAL PROPERTIES OF THE THIOCARBONYLTHIO COMPOUNDS FROM CONVENTIONAL DENSITY FUNCTIONAL THEORY CALCULATIONS.

Density functional theory (DFT) calculations employed at two levels, B3LYP/6-31G+(d) and B3P86/6-31G+(d), are reported for the geometry, enthalpy, and free energy of reaction of a number of dithiobenzoate reversible addition fragmentation transfer (RAFT) reagents (S=C(Ph)S–R, S=C(Z)S–CH₂Ph). Based on these theoretical data, the effectiveness of these RAFT reagents is analyzed. The conclusions, especially obtained at B3LYP/6-31G+(d) level, are in good agreement with the experimental results. Our calculations suggest that the dithiobenzoate (S=C(Z)S–CH₂Ph), where Z is OC₆H₅ or N(alkyl)₂, is a poor RAFT reagent. Contrarily, the compound S=C(Ph)S–R, where R is C(Me)₂Ph or C(Me)₂CN, is a highly efficient RAFT reagent. Our results reveal the utility of the theoretical calculations of physical magnitudes for the rationalization of judging the effectiveness of RAFT reagents and demonstrated that DFT is a good method to calculate these data. In addition, our results on the enthalpies and Gibbs free energies of formation for the R radicals are calculated with the same method. These data are important for the design of logical and economical chemical process. Finally, the B3LYP hybrid functional is employed to predict the values of thermodynamic magnitudes for several new ithiobenzoates. Those results need to be verified by future experimental measurements or theoretical calculations. [ABSTRACT FROM AUTHOR]