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The Effect of Intramolecular Hydrogen Bonds on the Rotational Barriers of the Biaryl C-C Axis
Zheng Dong1, Xiaoqiang Ma1, Yueyang Yu1
1Guangdong Provincial Key Laboratory of Chiral Molecule and Drug Discovery, School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou, 510006, China.
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.
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