Synthesis and Conformational Studies of Methylated, Highly Branched Fluoroolefins: Gear-Meshed Conformational Isomers

摘要

Methylated, highly branched fluoroolefins were prepared by treatment of hexafluoropropene trimers with CH_3Li and CH_3MgBr. Their structures, which included some rotational isomers, where determined by NMR and GC-MS and were further confirmed by B3LYP-GIAO calculation of NMR shieldings. Of the seven methylated fluoroolefins isolated in pure states, three were shown to be mixtures of pairs of conformational isomers. The methylated fluoroolefins containing two bulkyl geminal substituents such as (CF_3)_2CF and (CF_3)_2CCH_3 showed gear-meshed conformations in which the two bulky substituents were conformationally locked.