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|Title:||Effect of A1,3-strain on the stereochemistry of N-acetyl and N,O-diacetyl-r-2,c-6-diphenylpiperidin-4-one oximes|
|Keywords:||A1,3-strain;N-acetylpiperidin-4-one oximes;N,O-diacetylpiperidin-4-one oximes;NMR spectra;Semiempirical MO calculation;X-ray crystal structure;Variable temperature 1H NMR spectra|
|Abstract:||The stereochemical consequences of the introduction of A1,3-strain by means of acetyl groups in r-2,c-6-diphenylpiperidin-4-one oximes have been studied using various NMR spectral techniques, X-ray crystallographic analysis and semiempirical MO calculations. The NMR spectral results show that the N,O-diacetylpiperidin-4-one oximes 12-15 prefer to adopt twist-boat conformation with an equilibrium between syn and anti rotamers. From the variable temperature 1H NMR spectral studies carried out on N,O-diacetyl-t-3-methyl-r-2,c-6-diphenylpiperidin-4-one oxime 13, the syn-anti rotational barriers DG#AB and DG#BA have been found to be 44.2 and 43.5 kJ mol-1, respectively. The X-ray crystal structure of N,O-diacetyl-t-3-isopropyl-r-2,c-6-diphenylpiperidin-4-one oxime 14 also show twist-boat conformation. The conformational preferences obtained from the semiempirical MO calculations for N,O-diacetylpiperidin-4-one oximes 12-15 have been found to be similar to those predicted from the NMR spectral studies and X-ray crystallographic analysis. Similarly, the N-acetyl-r-2,c-6-diphenylpiperidin-4-one oximes 5-7 have been found to adopt twist-boat conformations.|
|Appears in Collections:||IJC-B Vol.51B(08) [August 2012]|
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