Cis-trans isomerism and conformational structure of N-methyldodecanelactam as studied by NMR, IR and Raman spectroscopy and by theoretical calculations

Abstract

In 1H and 13C NMR spectra of N-methyldodecanelactam (I) in CDCl3 and tetrachloroethane solution, the signals of various groups in cis and trans forms of (1) were assigned by means of two-dimensional COSY, HETCOR (heteronuclear correlation spectroscopy) and ROESY methods. The conformational structure of the first two bonds neighbouring the amide bond was determined from J couplings in 1H NMR spectra and theoretical calculations (MM2, AM1). The barrier to rotation about the amide bond was found from the temperature dependence of lineshapes in 1H and 13C NMR spectra. IR and Raman spectra of (I) were measured in the temperature range 25 to −140°C and the intensity changes of vibrational bands are discussed in connection with possible conformational transitions.