THE MEASUREMENT OF THE ONE-FOLD ROTATIONAL BARRIER OF ECLIPSED BONDS - A DYNAMIC NMR DETERMINATION OF N-O OR N-CH2 BOND ROTATION IN N-ALKOXY-2,2,6,6-TETRAMETHYLPIPERIDINES OR N-ALKYL-2,2,6,6-TETRAMETHYLPIPERIDINES

In a series of N-alkoxy- and N-alkyl-2,2,6,6-tetramethylpiperidines, the temperature dependence of NMR spectra shows that a conformational interconversion involving ring inversion, nitrogen inversion and rotation about the exocyclic bond takes place. Barriers to interconversion are reported. Except with the simplest N-substituents, the rate-determining step in the interconversion is rotation about the exocyclic bond at nitrogen, so the measured barriers represent the one-fold rotational barriers for that bond.