Density Functional Theory and X-ray Investigations of P- and M-Hexamethylene Triperoxide Diamine and Its Dialdehyde Derivative

Recently, we carried out a density functional theory B3LYP/6-31+G(d) study of hexamethylene triperoxide diamine (HMTD) in order to elucidate the unusual, nearly planar, sp² hybridization of the two bridgehead nitrogen atoms, each bonded to the three CH₂ groups. We postulated that extended bonding orbitals between peroxide oxygens results in charge delocalization which decreases lone-pair repulsion and compensates the energy loss due to the sp³ to sp² hybridization change on the nitrogen atoms. We have reexamined the crystal structure of HMTD by performing low-temperature, single-crystal X-ray studies, and we have determined that the unit cell contains a 50−50 racemic mixture of enantiomeric forms of HMTD, showing disorder about the mirror plane. At the low temperature, all hydrogen atoms were located and resolved, which was not previously possible. We have also crystallized and performed low-temperature X-ray analysis of a never previously reported dialdehyde form of HMTD, tetramethylene diperoxide diamine dialdehyde (TMDDD), which reveals enantiomers present in the unit cell without disorder. B3LYP density functional theory studies of HMTD and TMDDD are presented, as well as a transition state investigation of possible thermal interconversion of the HMTD enantiomers.