Stereoelectronic effects in brominations of cyclopropylarenes and 9-alkylanthracenes
| dc.contributor.author | Hakim, Mas Rosemal | en |
| dc.contributor.committeechair | Tanko, James M. | en |
| dc.contributor.committeemember | McGrath, James E. | en |
| dc.contributor.committeemember | Gibson, Harry W. | en |
| dc.contributor.committeemember | Taylor, Larry T. | en |
| dc.contributor.committeemember | Dorn, Harry C. | en |
| dc.contributor.department | Chemistry | en |
| dc.date.accessioned | 2015-07-09T20:43:13Z | en |
| dc.date.available | 2015-07-09T20:43:13Z | en |
| dc.date.issued | 1989 | en |
| dc.description.abstract | The free radical bromination of several cyclopropylarenes has been studied. The abstraction of a cyclopropyl hydrogen by bromine atom, which to date has been an unrecognized process, is demonstrated in this study. Specifically, when a cyclopropyl group is attached to the 9-position of an anthracene, an unprecedented hydrogen abstraction product, the corresponding cyclopropyl bromide, is obtained. This is believed to be due to stereoelectronic effects. Molecular mechanics calculations and X-ray crystallography have been used to demonstrate that 9-cycIopropylanthracene, unlike other cyclopropylarenes, is effectively locked in a conformation which places the a-cyclopropyl C-H bond in alignment with the p-orbitals of the aromatic system. This proper alignment activates the a-cyclopropyl hydrogen for abstraction by bromine atom. The relative reactivities of several 9-alkylanthracenes towards bromine atom are established, namely: 9-methyI- > 9-cyclopropyI- > 9-ethyl- >> 9-isopropylanthracene. Semi-empirical molecular orbital theory and molecular mechanics calculations have been utilized to demonstrate that the relative reactivities are not a function of bond dissociation energies but rather a function of the size of the dihedral angle between the a C-H bonds and the plane of the central ring of the various 9-alkylanthracenes in their lowest energy conformations. The absolute rate constants for the abstraction of hydrogen by bromine atom from 9-methyl-, 9-cyclopropyl-, and 9·ethylanthracene are estimated to be 1.1 x 10⁸ M⁻¹ sec⁻¹, 3.8 x 10⁷ M⁻¹ sec⁻¹ and 7.2 x 10⁶ M⁻¹ sec⁻¹ respectively. The value for the primary hydrogen/deuterium isotope effect for the abstraction of hydrogen by bromine atom from 9-cyclopropylanthracene is determined to be 2.6. All of the above observations lend support to the importance of stereoelectronic effects in the free radical bromination of the cyclopropylarenes and 9-alkylanthracenes. | en |
| dc.description.degree | Ph. D. | en |
| dc.format.extent | xii, 147 leaves | en |
| dc.format.mimetype | application/pdf | en |
| dc.identifier.uri | http://hdl.handle.net/10919/54185 | en |
| dc.language.iso | en_US | en |
| dc.publisher | Virginia Polytechnic Institute and State University | en |
| dc.relation.isformatof | OCLC# 20910245 | en |
| dc.rights | In Copyright | en |
| dc.rights.uri | http://rightsstatements.org/vocab/InC/1.0/ | en |
| dc.subject.lcc | LD5655.V856 1989.H333 | en |
| dc.subject.lcsh | Bromination | en |
| dc.title | Stereoelectronic effects in brominations of cyclopropylarenes and 9-alkylanthracenes | en |
| dc.type | Dissertation | en |
| dc.type.dcmitype | Text | en |
| thesis.degree.discipline | Chemistry | en |
| thesis.degree.grantor | Virginia Polytechnic Institute and State University | en |
| thesis.degree.level | doctoral | en |
| thesis.degree.name | Ph. D. | en |
Files
Original bundle
1 - 1 of 1