Preferred gauche conformation in N-(2-aminoethyl)pyridinium ions

Abstract

X-ray analysis of 1-[(2S, 3S)-2-N,N-dibenzylamino-3-methyl-1-pentyl]pyridinium p-toluenesulphonate and 1-[(2S)-2-N,N-dibenzylamino-1-propyl]pyridinium p-toluenesulphonate reveals that in both compounds the central N---C---C---N moiety is in the syn-clinal conformation. According to SCF-LCAO-MO calculations the syn-clinal conformation of the parent on, N-(2-aminomethyl)pyridinium is 23.4 kJ mol−1 lower in energy than the anti-periplanar conformation. The calculations suggest incipient bond formation between the amino nitrogen atom and the pyridinium ring in the syn-clinal conformation.