The synthesis end P.M.& spectra of some I-phenyl-j,&disubstituted G-laotams has recently been reported (1) and marked magnetic nonequivalence of benzylic CH2 protons in a number of N-benzyl oyclio amides has been records& (2,3). We now report the P.M.R. spectra of fourteen &lactams (Pip. 1) which show a number of interesting spectral features.
In these compounds (Table ) Jois > Jtrans, and these vioinal coupling constants are of the same sign and opposite in sign to the two geminal couplings Jj3, and J44'. Comparatively large cross-ring couplings between N-substituents and H3 or R3, are observed; and in the N-benzyl compounds, marked magnetic non-equivalence of the benzylic protons and stereospecific coupling to the C-3 protons in &substituted compounds suggests highly preferred conformations of the N-benzyl grouping.
We assume in the following discussion that the &laotam rillg is planar, but that the N-substituent is not coplanar with the ring atoms, a conclusion which is almost inescapable on the spectral evidence presented.
Chemical shift data are summarised in Table , coupling constants in Table 2, and long-range coupling constants in Table 3. 3325 3326 No.37 No.37 Chemiaal Shifts (DDlB.1 Relative to Tetranmthulsilene (iIltez?ULl~