We analyze the conformation of several members of the nylon l,n family with the linked-atom least-squares (LALS) methodology applied to X-ray and electron diffraction data and with quantum mechanical calculations. We concluded that new structures, characterized by a particular conformation of the isolated methylene unit between NH groups, are possible in this family of nylons. Close amide groups are oriented in opposite directions. Different conformations depending on the polymethylene segments between the carbonyl groups are also found and energetically studied according to the number of methylene carbons. In the case of an odd and low n value, a 3-fold helical conformation responsible for three hydrogen bond directions seems to be stabilized. On the other hand, polymers with an even n value are characterized by a 2/b symmetry and therefore a single hydrogen bond direction. This is the first time that these types of structures have been observed in aliphatic polyamides.