Stereomutation of Conformational Enantiomers of 9-Isopropyl-9-formylfluorene and Related Acyl Derivatives

Low-temperature NMR spectra show that the title compound exists as a pair of conformational enantiomers, generated by the restricted rotation about the C9−Pri bond, the corresponding interconversion barrier being 6.9 kcal mol−1. This interpretation is supported by theoretical (MM and DFT) calculations and by the experimental determination of the analogous barriers occurring in the related MeCO and ButCO derivatives.