The Effect of Intramolecular Hydrogen Bonds on the Rotational Barriers of the Biaryl C-C Axis.

Abstract

Axially chiral compounds are attracting more attention recently. Although hydrogen bonds are reported as a vital weak force that influences the properties of compounds, the effect of intramolecular hydrogen bonds on the atropisomerization of the Caryl -Caryl single bonds has not yet been well quantitatively investigated. Here, a series of axially chiral biaryl compounds were synthesized to study the effect of hydrogen bonds on the rotational barriers of the biaryl C-C axis. Experimental studies demonstrated that the rotational barrier of hydrogen bonding biaryl 9 was significantly lower (46.7 kJ mol-1 ) than biaryl 10 without hydrogen bonds. Furthermore, theoretical studies revealed that the intramolecular hydrogen bond stabilized the transition state (TS) of tri-ortho-substituted biaryl 9, relieving the steric repulsion in the TS. We believe that this study will provide chemists with a deeper understanding of the atropisomerization process of axially chiral biaryl compounds.