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Title: Competing A1,3-strain and Ph:Ph diaxial repulsion in oximes and semicarbazones of N-nitroso-r-2,c-6-diphenylpiperidin-4-ones
Authors: Vijayalakshmi, R
Muthukumar, M
Ponnuswamy, S
Jeyaraman, R
Keywords: A1,3-strain;N-nitroso-r-2,c-6-diphenylpiperidin-4-ones;oximes;semicarbazones;conformation;configuration;epimerization;NMR spectra;semiempirical MO calculation;twist-boat
Issue Date: Dec-2006
Publisher: CSIR
IPC Code: Int.Cl.8 C07D
Abstract: The effect of A1,3-strain introduced by N-NO group in N-nitroso-r-2,c-6-diphenylpiperidin-4-ones on the selectivity in the formation of oximes 14-18 and semicarbazones 19-22 has been studied. In general, the oximes and semicarbazones formed are the E isomers, exclusively, except in the cases of the oximation of 3-methyl-N-nitrosopiperidin-4-one and 3,5-dimethyl-N-nitrosopiperidin-4-one which have produced a mixture of E and Z isomeric oximes. Oximation of 3,5-dimethyl-N-nitrosopiperidin-4-one yields a mixture of two isomers 17 and 18 differing in the relative configurations of methyl group due to epimerization at C5. The configurations and preferred conformations of the oximes 14-18 and semicarbazones 19-22 of N-nitroso-r-2,c-6-diphenylpiperidin-4-ones have been determined using NMR spectral experiments and are found to prefer twist-boat conformations with an equilibrium between two rotameric states due to restricted rotation around N-NO bond. The semiempirical MO calculations performed on the nitrosamines 14-22 have also shown the preference of twist-boat conformations.
Page(s): 2720-2735
ISSN: 0975-0983(Online); 0376-4699(Print)
Appears in Collections:IJC-B Vol.45B(12) December 2006]

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