(1992) Cycloaddition reactions of a heterocyclic nitrone. Masters thesis, King Fahd University of Petroleum and Minerals.
|
PDF
10192.pdf Download (4MB) | Preview |
Arabic Abstract
-
English Abstract
A study of the regiochemical and stereochemical behavior of the addition reaction of a heterocyclic nitrone, 5,6-dihydro-1, 4-oxide with a series of alkenes has been carried out. The high degree of regiochemical control in these concerted reactions has been explained in terms of frontier molecular orbital treatment. Stereoselectivity in these cycloadditions has been explained in terms of steric factors and secondary orbital interactions. Rate constants for the cycloadditon of the heterocyclic nitrone with several alkenes have been determined at 36?C by 1H NMF spectroscopy. Differences in the rates of cycloadditions have been explained in terms of combination of various factors such as torsional strain, bond angle bending strain, and steric factors (non-bonded repulsion) in the transition state. The barrier to nitrogen inversion in the nitrone cycloaddition products has been determined by detailed band shape analysis of proton and carbon NMR spectra and were in the range of 66.3 to 72.9 kJ/mol. The chair inversion has been slowed, in one case to show the presence of the two forms of the cis isomers. The barrier to chair inversion is 41.5 kJ/mol as determined by proton NMR band shape analysis. Except in one case, the major conformational isomer is shown to be the cis conformer, which is in equilibrium with the minor trans conformer. A mechanistic study of peracid induced ring opening of several cycloadducts has been carried out. The orientation of the nitrogen lone pair dictates the regioselectivity of the ring opening which involves an intramolecular kinetic deprotonation of a nitroxonium ion intermediate. Synthesis of several intermediates which can lead to the synthesis of various heterocyclic nitrones has been made.
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | Chemistry |
| Department: | College of Chemicals and Materials > Chemistry |
| Committee Advisor: | Ali, Shaikh Asrof |
| Committee Members: | Al-Hamdan, A. and Perzanowski, Herman |
| Depositing User: | Mr. Admin Admin |
| Date Deposited: | 22 Jun 2008 13:58 |
| Last Modified: | 01 Nov 2019 13:58 |
| URI: | http://eprints.kfupm.edu.sa/id/eprint/10192 |