NMR study of nitrogen inversion and N-O bond rotation and anomeric effect in hydroxylamine derivativ...

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" NMR study of nitrogen inversion and N-O bond rotation and anomeric effect in hydroxylamine derivatives "
A. Hassan

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	1113088
Doc. No	:	TLpq304331609
Main Entry	:	A. Hassan
Title & Author	:	NMR study of nitrogen inversion and N-O bond rotation and anomeric effect in hydroxylamine derivatives\ A. Hassan
College	:	King Fahd University of Petroleum and Minerals (Saudi Arabia)
Date	:	1996
student score	:	1996
Degree	:	Ph.D.
Page No	:	187
Abstract	:	A multitude of nitrones are prepared by the condensation of aldehydes and hydroxylamines, which on reduction with NaBH4 gave the required hydroxylamines. The barriers to inversion in these acyclic di- and tri-substituted hydroxylamines are determined by H NMR bandshape analysis. The barriers range from 49.1 to 66.8 kJ mol The magnitude of the barriers are discussed in terms of a conformational process which involves nitrogen inversion and rotation around N-O bond. The N-benzyl group with an ortho hydroxy substituent increases the nitrogen inversion barrier by 10 kJ mol which indicates the requirement of breaking of the intramolecular hydrogen bond prior to inversion. In several series of compounds, having usd\rm XC\sb6H\sb4CH\sb2usd substituents attached to nitrogen, Hammet free energy correlations are obtained with positive usd\rhousd values, indicating increased electron density at the transition state for the inversion process. To shed more light on the nitrogen inversion process and anomeric effect a series of isoxazolidines are also synthesized, and their H and C NMR spectra recorded over a range of temperatures. Hammet plots were obtained to quantify the reaction constant usd\rho.usd Isoxazolidines with C(5) ethoxy substituents demonstrate a strong anomeric effect. Kinetic studies involving HgO and para benzoquinone oxidation of hydroxylamines to nitrones provided an insight to the mechanistic pathway the oxidation process traverses. The formation of E nitrones which quickly isomerize to the Z nitrone was also observed. This isomerization appears to be a bimolecular process.
Subject	:	aldehydes
	:	Chemistry
	:	nitrones
	:	Pure sciences