Line shapes ring inversion

Otherwise, the piperidine ring system was considered to be in the stable chair conformation. The two different experimental barriers to ring inversion and N-inversion of N-methylpiperidine were reconsidered. An accurate line shape analysis of the dynamic NMR spectra in the gas phase... 

In 1,1,4,4-tetramethylcyclohexane (50) the rate of ring inversion has been studied by line shape analysis of the methyl resonance at various temperatures. The results are compared with those obtained for the structurally similar acetone peroxide (51). In these two systems (50) and (51), the equilibria are between two identical chair conformers and single coalescence temperatures are observed ( —61°C and — 66°C at 60 Mc./sec., respectively). In duplodithioacetone (52) the more stable twist-boat conformer enters into the equilibrium, and... 

The energy barriers in the chair-chair inversion of hexahydro-1,3,5-trimethyl-1,3,5-triazine and several other alkyl derivatives (57, R = Me, Et, i-Pr, t-Bu) have been examined. The authors of the latter paper conclude that since AG is solvent independent, the observed effect is due to ring inversion and not inversion of the alkyl substituents on nitrogen. The former authors also examined hexa-methyl-l,3,5-trithiane (58) and s-trioxane (59). Ring inversion of 1,3-dimethyl- (60, R = Me) and 1,3-diethylhexahydropyrimidines (60, R = Et) has been studied by line-shape analysis at low temperatures. 

Anet FAL, Bourn AJR (1967) Nuclear magnetic resonance line-shape and double-resonance studies of ring inversion in cydohexane-d,j. J. Am. Chem. Soc. 89 760... 

A theoretical formalism for calculating dynamic multiple quantum NMR line shapes has been developed and used to calculate the expected line shapes of 1,3,5-trioxane dissolved in liquid crystalline solvents and undergoing ring inversion <1988JCP25>. It was shown that the resulting line shapes can be used to derive the kinetic parameters of the dynamic process. 

No spectral change was observed over a temperature range from 223- -323 K. Determination of activation energy for ring inversion by line shape analysis. 

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