CONFORMATIONS OF UNSYMMETRICAL N-T-BUTYL-N-SUBSTITUTED 2-PHENYLACETAMIDES

Various N-t-butyl-N-substituted 2-phenylacetamides, PhCH2CON(t-Bu)R, w herein R is methyl, ethyl, n-propyl, n-butyl, i-propyl, phenyl and cyc lohexyl, were synthesized, Depending on the kind of substituent on the nitrogen atom, some of the examined amides exist in different conform ational forms, H-1 NMR and C-13 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 distrib ution of cis and trans isomers has been established by means of differ ent coupling constants and the NOE difference technique, Information a bout fragmentation routes, and the effect of overall and partial struc tures were obtained by the study of the metastable ions, The results a re in accordance with our previous investigations of the structures of N,N-disubstituted 2-phenylacetamides. (C) 1997 Elsevier Science B.V.