CONFORMATIONAL STRUCTURE OF N-METHYL-8-OCTANELACTAM AND POLY(N-METHYL-8-OCTANELACTAM) AS STUDIED BY NMR, INFRARED AND RAMAN-SPECTROSCOPY AND BY THEORETICAL CALCULATIONS

It was proved by H-1 and C-13 NMR spectra that in N-methyl-8-octanelac tam in CDCl3 solution, the amide bond assumes only the cis form. Minor inversion about the plane of the amide bond occurs with an activation enthalpy Delta H# = 44.7 kJ/mol. Molecular mechanics and quantum mech anical calculations yielded four favoured conformational structures fo r the isolated molecule. By vibrational spectra, one of two distinguis hable structures strongly predominates. From H-1 NMR spectra, this pre dominant conformation was identified with one of the calculated stable forms. By C-13 NMR evidence, poly(N-methyl-8-octanelactam) in tetrach loroethane solution contains equal populations of the cis and trans am ide forms; the structure of this polymer in the rubbery solid state se ems to be similar to its structure in solution.