2 research outputs found
Elucidating the Role of Aromatic Interactions in Rotational Barriers Involving Aromatic Systems
The measurement of aryl-naphthyl rotational barriers,
Δ<i>G</i><sup>⧧</sup>, in various solvents
for two substituted
1,8-diarylnaphthalenes by dynamic <sup>1</sup>H NMR showed that Δ<i>G</i><sup>⧧</sup> trends in aromatic systems can be fully
rationalized only when considering the different types of aromatic
interactions that can be established in the ground and transition
states, namely, intramolecular interactions involving the aromatic
rings and specific solvation interactions
Phenylnaphthalenes: Sublimation Equilibrium, Conjugation, and Aromatic Interactions
In this work, the interplay between structure and energetics
in some representative phenylnaphthalenes is discussed from an experimental
and theoretical perspective. For the compounds studied, the standard
molar enthalpies, entropies and Gibbs energies of sublimation, at <i>T</i> = 298.15 K, were determined by the measurement of the
vapor pressures as a function of <i>T</i>, using a Knudsen/quartz
crystal effusion apparatus. The standard molar enthalpies of formation
in the crystalline state were determined by static bomb combustion
calorimetry. From these results, the standard molar enthalpies of
formation in the gaseous phase were derived and, altogether with computational
chemistry at the B3LYP/6-311++G(d,p) and MP2/cc-pVDZ levels of theory,
used to deduce the relative molecular stabilities in various phenylnaphthalenes.
X-ray crystallographic structures were obtained for some selected
compounds in order to provide structural insights, and relate them
to energetics. The thermodynamic quantities for sublimation suggest
that molecular symmetry and torsional freedom are major factors affecting
entropic differentiation in these molecules, and that cohesive forces
are significantly influenced by molecular surface area. The global
results obtained support the lack of significant conjugation between
aromatic moieties in the α position of naphthalene but indicate
the existence of significant electron delocalization when the aromatic
groups are in the β position. Evidence for the existence of
a quasi T-shaped intramolecular aromatic interaction between the two
outer phenyl rings in 1,8-di([1,1′-biphenyl]-4-yl)naphthalene
was found, and the enthalpy of this interaction quantified on pure
experimental grounds as −(11.9 ± 4.8) kJ·mol<sup>–1</sup>, in excellent agreement with the literature CCSD(T)
theoretical results for the benzene dimer