Conformational Studies by Dynamic NMR. 78.<sup>1</sup> Stereomutation of the Helical Enantiomers of Trigonal Carbon Diaryl-Substituted Compounds: Dimesitylketone, Dimesitylthioketone, and Dimesitylethylene
plane of carbonyl. The same structure was predicted by molecular mechanics calculations, which also produced good agreement between computed and experimental barriers for a dynamic process where a disrotatory one-ring flip pathway reverses the helicity of the conformational enantiomers. Solid-stateNMRspectra indicated that the enantiomerization barrier in the crystal must be much higher (at least