Structure, Conformation, and Stereodynamics of the Atropisomers of Highly Hindered Benzyl Ethers Daniele Casarini Carmine Coluccini Lodovico Lunazzi Andrea Mazzanti 10.1021/jo0603173.s002 https://acs.figshare.com/articles/journal_contribution/Structure_Conformation_and_Stereodynamics_of_the_Atropisomers_of_Highly_Hindered_Benzyl_Ethers/3076555 Low-temperature and NOE NMR spectra of four of the title compounds indicate that they adopt a synclinal (sc) conformation, in agreement with the prediction of ab initio computations. In the case of the most-hindered derivative (compound <b>4</b>), the conformation is syn-periplanar (sp), as is also shown by X-ray diffraction. Such stereolabile sp- or sc-atropisomers exist as two conformational enantiomers:  the corresponding enantiomerization barriers, covering the range 6.6 to 9.7 kcal mol<sup>-1</sup>, could be measured for all the examined compounds. In two cases (compounds <b>3</b> and <b>5</b>), the minor antiperiplanar (ap) atropisomer has been also observed, and the sc to ap interconversion barrier measured (11.7 and 11.9 kcal mol<sup>-1</sup>, respectively). In addition, restricted rotation of the isopropyl and <i>tert</i>-butyl substituents has been detected, and the corresponding barriers have been determined. 2006-06-09 00:00:00 ap interconversion barrier mol range 6.6 conformation title compounds NOE NMR spectra enantiomerization barriers compounds 3 sc ab initio computations kcal Such stereolabile sp