Monoclinic and Triclinic Tetraisopropyl‐<i>p</i>‐phenylenediamine: To what Extent do n_N/π Interactions Determine Structures?

Abstract

Two conformations-two crystal forms! This is the case for the title compound. The crystal of the conformer with nN/π interactions between the nitrogen lone pairs and the benzene π system (left) is monoclinic, whereas that of the conformer without this interaction (right) is triclinic. The dihedral angles ω (C2NC6) are 28 and 74°. According to potential energy surface calculations, the conformers have almost identical enthalpies of formation (ΔH = −46 and −47 kJmol−1).