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- or N-alkyl-2,2,6,6-tetramethylpiperidines

Abstract

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.