Conformational Features of N-Trifluoromethyl Amides and Thioamides

Abstract

We investigated the structural and conformational features of N-trifluoromethyl (N-CF₃) (thio)amides using X ray and VT NMR analyses. These compounds showed lower rotational barriers and generally reduced cis populations compared with their N-methyl analogues. N-CF₃ thioamides did not prefer cis conformations in solution or the crystalline state, while computational studies suggest the electronic effect of the CF₃ such as the attenuation of the negative electrostatic potential on the thiocarbonyl sulfur also plays a role. These findings should be helpful in the design of new fluorinated functional molecules.