Substituent Effects on the Stability of Arene−Arene Complexes:  An AM1 Study of the Conformational Equilibria ofcis-1,3-Diphenylcyclohexanes

Abstract

Molecular orbital calculations at the AM1 level have been performed on cis-1,3-diarylcyclohexane systems (1, 2) in order to provide a theoretical model and suggest novel experimental models for the investigation of arene−arene π-stacking. Energy minima were located for diaxial conformers (a) in which aryl rings are coplanar and π-stacked and (b) in which aryl rings adopt an edge-to-face or intermediate conformation. The average face-to-face distance varies from 4.1 to 4.4 Å, outside the van der Waals contact distance of 3.4 Å, and the minimum inter-ring distance varies from 3.1 to 3.5 Å. The diaxial−diequatorial conformational equilibria (ΔE ax - eq) were calculated for a large series of para-substituted and meta-substituted 1,3-diarylcyclohexanes and plotted against Σσp, Δσp, and E HOMO − E LUMO. The best correlation was observed using electrostatic potentials calculated at the electron density surface on the π-face of individual arenes. Similar correlations were observed for conformational equilibria associated with the improved 1,3-dimethyl-1,3-diarylcyclohexane series (3). More limited correlations were drawn for the diaxial−diequatorial conformational equilibria involving (i) edge-to-face diaxial cis-1,3-diarylcyclohexanes and (ii) π-stacked diaxial cis-1,3-diarylcyclohexanes in which one aryl ring is perfluorinated (5, 6). In all cases, the results (a) showed good agreement with literature data on related experimental systems and (b) demonstrated the dominance of arene−arene electrostatic contributions to conformational energy over the negligible orbital mixing and charge-transfer interactions.

Ferrocenyl‐Pyrenes, Ferrocenyl‐9,10‐Phenanthrenediones, and Ferrocenyl‐9,10‐Dimethoxyphenanthrenes: Charge‐Transfer Studies and SWCNT Functionalization

“…In case of 10 and 12 , the parallel displaced π‐interactions between the arenes led to the formation of 1D ( 12 ) and 2D coordination polymers ( 10 ) along the a ‐ ( 10 ) or b ‐axis ( 12 ), resulting in the formation of columns (for more details, see Figures SI11 and SI12 in the Supporting Information). The columnar structure of 12 is based on the parallel displaced π‐interactions involving C11–C16 of the phenanthrene with centroid–centroid distances of 5.165(12) Å, exceeding the criterion for π‐stacking (3.3–3.8 Å) . However, owing to displacement from ideal stacking, short distances between C13/C14/C16 and their symmetry equivalents of the adjacent molecule of 3.04(3)–3.39(3) Å were found, indicating strong π–π interactions …”

“…The columnar structure of 12 is based on the parallel displaced p-interactions involving C11-C16 of the phenanthrene with centroid-centroid distances of 5.165 (12) ,e xceeding the criterionf or p-stacking (3.3-3.8 ). [54][55][56] However,o wing to displacement from ideal stacking, short distances between C13/C14/C16 and their symmetry equivalents of the adjacent molecule of 3.04(3)-3.39(3) werefound, indicating strong p-p interactions. [54][55][56] Compound 10 builds a2 Dc oordinationp olymer,w hereby both molecules of the asymmetric unit are responsible for the columnar structure.…”

“…[54][55][56] However,o wing to displacement from ideal stacking, short distances between C13/C14/C16 and their symmetry equivalents of the adjacent molecule of 3.04(3)-3.39(3) werefound, indicating strong p-p interactions. [54][55][56] Compound 10 builds a2 Dc oordinationp olymer,w hereby both molecules of the asymmetric unit are responsible for the columnar structure. Parallel displaced p-interactionsb etween the ferrocenyl's cyclopentadienylsi nterconnect the columns.…”

Pentafluorophenyl–Phenyl Interactions in Biphenyl‐DNA

“…[15] The stacking of aromatic hydrocarbons on the corresponding fluorohydrocarbons has been especially well investigated. [23,24] This knowledge is being applied in the field of crystal engineering. [16] These two compounds, both liquids at room temperature, form a solid aggregate, [17] which is characterized by not only alternating p stacks, but also lateral alternation between hexafluorobenzene and benzene rings.…”

Theoretical analysis of counterfoil influence over the physicochemical properties of aniline tetramers in several oxidation states

“…The AM1 method has been extensively used to calculate oligomer structures and gives good results for geometric parameters [14,16,17]. Even though this Vaschetto, Retamal, Contreras, and Zagal method does not provide good quantitative results for energy values, it gives good qualitative correlations [ 14].…”