An Unexpected Atropisomerically Stable 1,1‐Biphenyl at Ambient Temperature in Solution,Elucidated by Vibrational Circular Dichroism (VCD)

Biphenyls with only two substituents at the ‘peri'‐position normally show rotation about their chiral axis at room temperature. Using vibrational circular dichroism (VCD), we found no evidence for rotation of (P)‐2′‐(4S)‐4,5‐dihydro‐4‐(1‐methylethyl)oxazol‐2‐yl]1,1′‐biphenyl]‐2‐methanol ((P,S)‐ 1 ) in CDCl₃ about its chiral axis due to stabilization by intramolecular H‐bonding. All rotamers of 1 were calculated at the DFT level, and, from these optimized structures, the VCD spectra were calculated and compared to the measured VCD spectra. The best agreement between calculated and measured spectra is obtained when two rotamers are present in solution. These rotamers differ primarily in their intramolecular H‐bonding interactions, having either OH???N (the form present in the solid state) or OH???O H‐bonds, i.e., a rotation of the heterocycle in 1 takes place in solution.