Hindered rotation in N-methylformamide. A peptide-bond model system.

Barriers to rotation about the C-N bond in the cis and trans isomers of N-methylformamide have been determined by n.m.r. spectroscopy. Representative values are 20.7 and 22.0 kcal/mole. Arrhenius parameters have also been determined. These results are compared with C-N barriers for N,N-dimethylformamide and unsubstituted formamide. The data suggest that C-N rotational barriers for N-methyl amides may be similar to those for their N,N-dimethyl derivatives. Energy requirements for rotation about the central C-N bond in amides (i) are of potential interest to those engaged in % 72 >C N\ R 1 R 3 1