Conformational effects in compounds with 6-membered rings—XIII : Detection of twist conformers using 13C NMR chemical shifts

¹³C NMR spectra of derivatives of cyclohexane, piperidine, and thian in chair and twist eonformers, and of model compounds, lead to estimates of deshielding (Δδ = 3.6 ± 0.2 ppm) for axial C$\text{Me}$₃ on a cyclohexane ring and shielding (Δδ = ?0.2 to ?0.6 ppm) for ψe-C$\text{Me}$₃ in twist conformers, relative to equatorial C$\text{Me}$₃. Ring carbon atoms are considerably shielded in twist conformers relative to chair eonformers. The value of ¹³C chemical shifts in the study of chair-twist equilibria is exemplified by variable temperature measurements on diastereomeric pairs of compounds (11 and 13; 38 and 50).