Collect. Czech. Chem. Commun. 1995, 60, 1798-1808

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

Jiří Dybal, Danica Doskočilová, Bohdan Schneider and Rudolf Puffr

Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic


It was proved by 1H and 13C NMR spectra that in N-methyl-8-octanelactam in CDCl3 solution, the amide bond assumes only the cis form. Mirror inversion about the plane of the amide bond occurs with an activation enthalpyH# = 44.7 kJ/mol. Molecular mechanics and quantum mechanical calculations yielded four favoured conformational structures for the isolated molecule. By vibrational spectra, one of two distinguishable structures strongly predominates. From 1H NMR spectra, this predominant conformation was identified with one of the calculated stable forms. By 13C NMR evidence, poly(N-methyl-8-octanelactam) in tetrachloroethane solution contains equal populations of the cis and trans amide forms; the structure of this polymer in the rubbery solid state seems to be similar to its structure in solution.