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

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. Here, we show that the transition state of atropisomerization of tri-ortho-substituted biaryl was stabilized by intramolecular hydrogen bonds, resulting in a significant reduction in the steric repulsion around C-C axes and a decrease in the energy barrier of atropisomerization (& UDelta;& UDelta;G & NOTEQUAL;(10-9)=46.7 kJ/mol).image

Automated summary

This study investigates the effect of intramolecular hydrogen bonds on the rotational barriers of axially chiral biaryl compounds. The experimental results show that compounds with hydrogen bonds have significantly lower rotational barriers. Theoretical studies reveal that intramolecular hydrogen bonds stabilize the transition state, reducing steric repulsion. This study provides important insights into the atropisomerization process of axially chiral biaryl compounds.