عنوان

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

Number

TLpq304331609

.Language of Text, Soundtrack etc

انگلیسی

Title Proper

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

General Material Designation

[Thesis]

First Statement of Responsibility

A. Hassan

Name of Publisher, Distributor, etc.

King Fahd University of Petroleum and Minerals (Saudi Arabia)

Date of Publication, Distribution, etc.

1996

Specific Material Designation and Extent of Item

187

Dissertation or thesis details and type of degree

Ph.D.

Body granting the degree

King Fahd University of Petroleum and Minerals (Saudi Arabia)

Text preceding or following the note

1996

Text of Note

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.

aldehydes

Chemistry

nitrones

Pure sciences

A. Hassan

Electronic name

p

[Thesis]

276903

a

Y