DFT study of the group interactions in 1,3,5-triamino-2,4,6-trinitrobenzene and 1,3,5-triamino-2,4,6-tridifluoroaminobenzene

Density functional calculations on isodesmic disproportionation reactions of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and 1,3,5-triamino-2,4,6-tridifluoroaminobenzene (TATDB) indicate that the interaction between nitro groups on meta carbons of TATB, which brings about unstability to the molecule, is surprisingly larger than that between difluroamino groups in TATDB. The electron-withdrawing and electron-donating groups generate large positive and very small negative values of E-disproportion, respectively. When both electron-withdrawing and electron-donating groups are attached to the benzene skeleton at the same time, large negative disproportionation energy is produced, which stabilizes the derivatives. The values of E-disproportion for TATB and TATDB are predicted to be -48.03 kJ/mol and -63.54 kJ/mol, respectively, indicating that the total interaction among groups with stabilization effects in TATDB is larger than that in TATB. The large difference of the Edisproportion values between TATB and TATDB is derived from the large difference between the interactions of the meta-nitro group and those of meta-difluoroamino groups. The energy barriers for the C-N internal rotation of NO2 group and NF2 groups are 74.7 kJ/mol and 185.8 kJ/mol for TATB and TATDB, respectively. The large energy barrier for the rotation of the NF2 group is caused by its stabilization interaction with neighbor amino groups, instead of steric effects. When the number of pairs of amino-nitro or amino-difluoroamino groups increases, there are more negative charges on the NO2/NF2 groups and on the O/F atoms.