Conformational preferences of model aliphatic diamides: Effect of the methyl side group on the polymethylene segment

The conformational preferences of N-[3-(acetylamino)-2-methyltrimethylene] acetamide and N-[5-(acetylamino)-(S) -2-methylpentamethylene] acetamide wer e investigated using ab initio computational methods. These are model compo unds of a number of substituted nylons m,n containing a methyl side group i n the diamine unit. A comparison with the results obtained for their linear analogues have allowed us to determine the influence of the methyl side gr oup on the conformational preferences of aliphatic diamides. Furthermore, t he conformations compatible with the electron and X-ray diffraction data re cently obtained for the related substituted nylons-m,n were identified.