Abstract
A number of substituted derivatives of 2,3-dimethyl-2,3-diazabicyclo[2.2.1]-5-heptène, Ib, have been prepared. The study of the NMR spectra of these compounds allowed us: 1. to identify the signals and the coupling constants due to the various protons and to study the effect of the orientation of an electronic lone-pair of an heteroatom linked to a HCCH groups on the vicinal 3J HH coupling; 2. to determine the steric effects of various groups X on the relative stability of the two invertomers A and B; 3. to give a clear illustration of the effects of specific solvation of form A in water on the conformational equilibrium A ⇌ B and on the effective ( or apparent) size of the substituents X. Some substituent effects on the nitrogen inversion barrier in derivatives of Ib are described. Furthermore the presence of an n → π* absorption band in the UV spectra of various compounds of type Ib points to the existence of an homoconjugative interaction between an endo lone-pair on nitrogen and the carbon-carbon double bond.
Published Version
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