Journal of Organic Chemistry p. 4721 - 4726 (1987)
Update date:2022-08-30
Topics:
Casarini, D.
Lunazzi, L.
Placucci, G.
Macciantelli, D.
Observation of anisochronous NMR signals in N-alkyl-N-methyl-1-naphthylamines at low temperature indicates that these molecules adopt a twisted conformation (yielding enantiomeric conformers at the equilibrium) as opposed to the corresponding N-alkyl-N-methyl-2-naphthylamines which give two planar (thus achiral) conformers.The barriers to enantiomerization in 1-naphthylamines have been measured by line-shape analysis for those amines containing prochiral substituents.The use at low temperature of one of the Pirkle's chiral alcohols as a discriminating agent allowed these barriers to be measured even in absence of prochiral grpups.Related alkyl 1-naphthyl nitroxides were also shown to prefer a twisted conformation, but the enantiomerization barriers are too low to be measured by ESR.Examination of a much more hindered nitroxide (2-tert-butyl-1-naphthyl ethyl nitroxide) showed that the methylenic hydrogens were anisochronous even at room temperature, indicating that this radical exist as a racemic mixture.The existence of an exponential relationship between the free energies of enantiomerization in the 1-naphthylamines and the nitrogen hyperfine splittings in the analogous nitroxides allowed the barrier for N,N-dimethyl-1-naphthylamine to be estimated.This barrier could not be measured directly because of the symmetry of the amine.
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