Conformations of unsymmetrical N-t-butyl-N-substituted 2-phenylacetamides

Abstract

Various N-t-butyl-N-substituted 2-phenylacetamides, PhCH 2 CON(t-Bu)R, wherein R is methyl, ethyl, n-propyl, n-butyl, i-propyl, phenyl and cyclohexyl, were synthesized. Depending on the kind of substituent on the nitrogen atom, some of the examined amides exist in different conformational forms. 1 H NMR and 13 C NMR spectra of these unsymmetrically N,N-disubstituted amides have been studied and peaks have been assigned in each case to the two possible conformational isomers, arising from the lack of free rotation about the C(O)-N bond. The relative distribution of cis and trans isomers has been established by means of different coupling constants and the NOE difference technique. Information about fragmentation routes, and the effect of overall and partial structures were obtained by the study of the metastable ions. The results are in accordance with our previous investigations of the structures of N,N-disubstituted 2-phenylacetamides.