Carbon‐13 NMR studies of thyroid hormones and model compounds. The conformational analysis of diphenyl ethers

The 13 C spectra of a series of thyroid hormones and derivatives including thyroxine (T 4 ) sodium salt, T 4 ‐ N ‐acetyl methyl ester, triiodothyronine (T 3 ), T 3 ‐sodium salt, T 3 ‐methyl ester hydrochloride, sodium triiodothyroacetate and ethyl triiodothyropropionate were assigned using chemical shift trends from model compounds, coupling constants and relaxation times. The 13 C spectra of a series of diphenyl ethers were assigned and the chemical shift trends observed were analyzed on the basis of conformational changes engendered by mesomeric or steric effects.