Synthesis, Structural, and Intriguing Electronic Properties of Symmetrical Bis-Aryl-α,β-Unsaturated Ketone Derivatives

Three symmetrical bis-aryl-α,β-unsaturated
ketone derivatives, 2,6-di((E)-benzylidene)-cyclohexan-1-one
(DBC), 2,6-bis((E)-4-chlorobenzylidene)cyclohexan-1-one
(BCC), and (1E,1′E,4E,4′E)-5,5′-(1,4-phenylene)bis(2-methyl-1-phenylpenta-1,4-dien-3-one)
(PBMP), have been prepared using the aldol condensation
approach toward ketones having two enolizable sites. The structures
of DBC, BCC, and PBMP have been resolved
via spectrometric methods. Moreover, the crystal structure of PBMP is determined by the single-crystal X-ray diffraction
(SC-XRD) technique, which revealed that the PBMP molecular
assembly is stabilized by the intermolecular C–H···O
bonding and C–O···π and weak T-shaped
offset π···π stacking interactions. The
Hirshfeld surface analysis (HSA) of the PBMP crystal
structure was performed as well, and the results were compared with
the results of DBC and BCC. The density
functional theory (DFT) study results revealed that the longer conjugated
molecule of PBMP has smaller but still quite significant
HOMO–LUMO gaps compared to the smaller molecules of BCC and DBC. The natural population analysis (NPA) and
natural bonding orbital (NBO) analysis were performed. Accordingly,
the hydrogen bonding and dipole–dipole interactions stabilize
the crystal structures of these compounds. Additionally, the NBO analysis
showed numerous high-energy stabilizing interactions for the PBMP compound due to the presence of numerous delocalized
and relatively easily polarizable π-electrons, thus implying
its significant thermodynamic stability. According to the global reactivity
parameter (GRP) analysis, the compounds BCC and DBC are relatively stable in redox processes and have high
thermodynamic stability and relatively lower reactivity in general.
The molecular electrostatic potential (MEP) analysis results imply
potential formation of the intermolecular hydrogen bonding and dispersion
interactions, which stabilizes the crystal structures of these compounds.