The IR spectra, the NIR spectra and the conformation of some basic amides

Abstract

The NH stretching region in a series of basic primary and secondary amides have been examined, discussed and some norms, which allow a distinction between inter and intramolecular hydrogen bonds have been drawn. Basic amide molecules are found to be strongly associated in chloroform, but far less in dichloromethane solution. When certain steric conditions are satisfied, a strong intramolecular NH … N. bond can be formed and it is detected by the appearance of a strong and broad band at ca. 3220 cm −1 (dichloromethane solution), by a shift of the amide I band (1660 instead of 1675 cm −1) and by an absorption band in the NIR at 1·980 μ. By determining the extent of the intramolecular hydrogen bond the conformation of 1-methyl-4-phenylisonipecotamide, tetrahydro-3-quinolinecarboxamides, hexahydronicotamides and β-N-piperidinopropionamides has been ascertained. The energy of the intramolecular NH … N hydrogen bond has been valued to be about 1 kcal/mole.