Nicethamid‐Analoge, V Untersuchungen zur gehinderten internen Rotation bei N,N‐Dimethylpyridinamiden

Abstract

Die Synthese von homologen, vinylogen und kernalkylierten N,N-Dimethyhicotinamiden wird beschrieben und die Energiebarriere bei der gehinderten Rotation der Amidgruppe mittels IH-NMR-Spektroskopie bestimmt.The synthesis of homologue, vinylogue and ringalkylated N,N-dimethyl nicotinamides is described and the energy barrier of the hindered rotation of the amide group determined by means of 1H-n. m. r. spectroscopy.

Absolute conformation of 3-(N-methyl-N-benzyl)carbamoyl-1,2,4-trimethylpyridinium iodide (I) and absolute configuration of 3-[N-methyl-N-(R)-α-methylbenzyl]carbamoyl-1,2,4-trimethylpyridinium iodide (II)

“…However, such a rotation about the C(9)--C(10) bond is sterically impossible, because it results in contact distances between H atoms of C (7) and C (12) of less than 0.6 A. The only way to circumvent this crowding would be a concerted process involving also a rotation about the N(1)-C(9) acid amide bond, which is known to have a high barrier of rotation in N,N-dialkylpyridinamides (Sattler & Schunack, 1975). So two factors seem to be responsible for the observed stability of the dissymmetric conformer of (I) in solution: (Johnson, 1976) and atom-numbering schemes.…”