Dynamic13C N.M.R. studies

Abstract

The ¹³C nuclear magnetic resonance technique has been applied to dynamical processes occurring in a number of compounds for which a ¹H study would be difficult, owing to complications in the proton spectra. Simple ¹³C signals in the proton-decoupled spectra are very convenient. The ¹³C line shapes at various temperatures have been analysed, to give the activation barriers to rotation around the C-N bond in stereoisomeric 2-phenylcyclopropanecarboxylic acid N,N-diethylamides (ΔH ^‡ = 16·7 ± 0·5 kcal/mole, ΔS ^‡ = -0·6 ± 1·6 e.u. for the trans isomer; ΔH ^‡ = 18·4 ± 0·6 kcal/mole, ΔS ^‡ = 2·8 ± 1·9 e.u. for the cis isomer), around the Ar-N(O) bond in p-nitroso-N,N-dimethylaniline (ΔH ^‡ = 14·5 ± 0·6 kcal/mole, ΔS ^‡ = 4·0 ± 2·0 e.u.), around the C-C bond in 9-chloromethyltriptycene (ΔH ^‡ = 13·5 ± 0·7 kcal/mole, ΔS ^‡ = -1·8 ± 2·5 e.u.) and to the nitrogen inversion in N-(1,2-dicarbomethoxyethyl)-aziridine (ΔH ^‡ = 21·8 ± 0·9 kcal/mole, ΔS ^‡ = 10·6 ± 3·6 e.u.).