The 1224 and 1323 cm−1 infrared bands in nylon 66 have previously been assigned to a unique conformation in a tightly folded chain with adjacent reentry. The unique conformation in the fold giving rise to these bands is a nitrogen-methylene bond that is between cis and trans. Models of the cyclic monomer and dimer of Nylon 66 indicate that this type of nitrogen-methylene bond exists in these compounds also. Since these cyclic oligomers must exhibit “adjacent reentry,” the fact that the 1224 and 1323cm−1 bands appear with greatly enhanced intensity in the infrared spectra of these compounds strongly supports the original assignment of these bands. It should be noted that in the infrared spectra of the linear oligomers these bands are absent. Copyright © 1969 by Marcel Dekker, Inc.
