Phenylnaphthalenes: Sublimation Equilibrium, Conjugation, and Aromatic Interactions

authors	Lima, CFRAC; Rocha, MAA; Schroder, B; Gomes, LR; Low, JN; Santos, LMNBF
nationality	International
journal	JOURNAL OF PHYSICAL CHEMISTRY B
keywords	PI-PI INTERACTIONS; MOLECULAR SYMMETRY; ORGANIC-COMPOUNDS; HEAT-CAPACITY; CRYSTAL-STRUCTURE; MELTING-POINT; SMALL SAMPLES; X-RAY; ENTROPY; NAPHTHALENE
abstract	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 T = 298.15 K, were determined by the measurement of the vapor pressures as a function of T, 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 alpha position of naphthalene but indicate the existence of significant electron delocalization when the aromatic groups are in the beta 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(-1), in excellent agreement with the literature CCSD(T) theoretical results for the benzene dimer.
publisher	AMER CHEMICAL SOC
issn	1520-6106
year published	2012
volume	116
issue	11
beginning page	3557
ending page	3570
digital object identifier (doi)	10.1021/jp2111378
web of science category	Chemistry, Physical
subject category	Chemistry
unique article identifier	WOS:000301766700009