Phenylnaphthalenes: sublimation equilibrium, conjugation, and aromatic interactions

Area of Science:

• Physical Chemistry
• Organic Chemistry
• Computational Chemistry

Background:

• Understanding structure-energetics relationships is crucial for designing novel organic molecules.
• Phenylnaphthalenes represent a class of compounds with potential applications where precise control over electronic and structural properties is key.

Purpose of the Study:

• To investigate the interplay between molecular structure and energetics in representative phenylnaphthalenes.
• To determine thermodynamic properties and relative molecular stabilities using experimental and theoretical methods.

Main Methods:

• Vapor pressure measurements using a Knudsen/quartz crystal effusion apparatus to determine sublimation thermodynamic quantities.
• Static bomb combustion calorimetry to measure standard molar enthalpies of formation in the crystalline state.
• Computational chemistry (B3LYP/6-311++G(d,p) and MP2/cc-pVDZ) and X-ray crystallography for structural and energetic analysis.

Main Results:

• Sublimation thermodynamics indicate molecular symmetry and torsional freedom significantly impact entropic differentiation, while surface area influences cohesive forces.
• Lack of significant conjugation observed between aromatic moieties in the alpha position of naphthalene.
• Significant electron delocalization found when aromatic groups are in the beta position.
• Quantified a quasi T-shaped intramolecular aromatic interaction in 1,8-di([1,1'-biphenyl]-4-yl)naphthalene experimentally.

Conclusions:

• Aromatic group position in phenylnaphthalenes dictates the extent of electron delocalization.
• Molecular symmetry, torsional freedom, and surface area are key factors governing sublimation energetics.
• Experimental and theoretical approaches provide complementary insights into phenylnaphthalene stability and interactions.