How great is the stabilization of crowded polyphenylbiphenyls by London dispersion?

• Type: Article in International Scientific Journal
• Date: 2023

Authors

Lima, CRAC (Author) FCUP; Mague, JT (Author) Other; Du, YC (Author) Other; Pascal, RA (Author) Other; Luis M N B F Santos (Author) FCUP

Journal

Title: Physical Chemistry Chemical Physics

Vol. 25

ISSN: 1463-9076

Publisher: Royal Society of Chemistry

Indexing

ISI Web of Knowledge - 1 Citation

Scopus - 1 Citation

Other information

Authenticus ID: P-00Y-CSB

DOI: 10.1039/d2cp05085d

Abstract (EN): Decaphenylbiphenyl (1) and 2,2',4,4',6,6'-hexaphenylbiphenyl (2) are bulky molecules expected to be greatly destabilized by steric crowding. Herein, through a combined experimental and computational approach, we evaluate the molecular energetics of crowded biphenyls. This is complemented by the study of phase equilibria for 1 and 2. Compound 1 shows a rich phase behavior, displaying an unusual interconversion between two polymorphs. Surprisingly, the polymorph with distorted molecules of C-1 symmetry is found to have the highest melting point and to be the one that is preferentially formed. The thermodynamic results also indicate that the polymorph displaying the more regular D-2 molecular geometry has larger heat capacity and is probably the more stable at lower temperatures. The melting and sublimation data clearly reveal the weakening of cohesive forces in crowded biphenyls due to the lower molecular surface area. The experimental quantification of the intramolecular interactions in 1 and 2 indicated, using homodesmotic reactions, a molecular stabilization of about 30 kJ mol(-1). We attribute the origin of this stabilization in both compounds to the existence of two parallel-displaced pMIDLINE HORIZONTAL ELLIPSISp interactions between the ortho-phenyl substituents on each side of the central biphenyl. Computational calculations with dispersion-corrected DFT methods underestimate the stabilization in 1, unless the steric crowding is well balanced in a homodesmotic scheme. This work demonstrates that London dispersion forces are important in crowded aromatic systems, making these molecules considerably more stable than previously thought.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 17