High-Yielding Syntheses, Crystal Structures and Hirshfeld Surface Analysis of Bis-1,1′-(2-nitropropenes) Extended with Benzene-1,4-diyl and Biphenyl-4,4′-diyl Spacers

Crystal structures of two 2-nitropropene derivatives, namely 1,4-bis((E)-2-nitroprop-1-enyl)benzene and 4,4′-bis((E)-2-nitroprop-1-enyl)biphenyl, support relevance of lone pair-π-hole interactions of nitro groups to the crystal packing of extended polyaromatic molecules. For the former structure, these bonds complement slipped π–π interactions of the benzene rings within a basic supramolecular motif representing infinite stacks. In the biphenyl derivative, only one out of two nitro groups afford NO₂⋯NO₂ bonds (N⋯O = 3.191(2) Å) as a local pattern. The decreased significance of lone pair-π-hole interactions is in line with growing contribution of weak dispersion forces, which favor close alignment of the molecules and larger interaction areas to generate multiple C–H⋯π bonds. Different types of C–H⋯O, C–H⋯π, π–π, NO₂–π, NO₂⋯NO₂, tetrel CH₃⋯O and CH₃⋯π bonds, which actualize in the present structures were further assessed by Hirshfeld surface analysis and intermolecular interaction energies were calculated using the CE B3LYP/6 31G(d,p) energy model. In addition, the facile and high-yielding preparations by condensation of dialdehydes and nitroethane, provide a straightforward access to the present 2-nitropropenes, as valuable synthetic intermediates.

The X-ray structures of 1,4-bis((E)-2-nitroprop-1-enyl)benzene and 4,4′-bis((E)-2-nitroprop-1-enyl)biphenyl reveal coexistence and interplay of lone pair-π-hole NO₂⋯NO₂ bonds, weak hydrogen and tetrel bonds and aromatic interactions.