| dc.contributor.author | Chan, Mary S. W. | en_US |
| dc.date.accessioned | 2014-10-21T12:37:56Z | |
| dc.date.available | 1998 | |
| dc.date.issued | 1998 | en_US |
| dc.identifier.other | AAINQ36574 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55586 | |
| dc.description | The regiochemistry of nucleophilic addition to the radical cations of simple alkenes and dienes was studied. Three nonsymmetric dienes [4-methyl-1,3-pentadiene (5), 2,4-dimethyl-1,3-pentadiene (6) and 2-methyl-1,3-butadiene (7)] and two alkenes [2-methylpropene (8) and 2-methyl-2-butene (9)] were examined in detail with methanol or fluoride ion serving as the nucleophile. The regioselectivity of each alkene or diene was determined by the product ratio from the photochemical nucleophile-olefin, combination aromatic substitution (photo-NOCAS) reaction. The relative stabilities of the reaction intermediates were estimated with ab initio molecular orbital calculations. | en_US |
| dc.description | Distonic radical cations are initially formed upon the addition of methanol to the alkene or diene radical cation. The relatively low energy of the bridged structure provides a pathway for the equilibration of the two alternative open structures at the distonic radical cation stage. The regiochemistry is determined by irreversible deprotonation from the oxygen to form beta-alkoxyalkyl radicals. The product resulting from the more stable beta-alkoxyalkyl radical is favored, implying that the regiochemistry of methanol addition is thermodynamically controlled. | en_US |
| dc.description | The possibility of a bridged structure does not exist for beta-fluoroalkyl radicals. This eliminates the opportunity for the equilibration of the radical intermediates. The addition of fluoride occurs in a single irreversible step. Therefore, the product distribution is not a reflection of the thermodynamic stability of these radical intermediates. There is evidence to suggest that polar and steric factors are important. This leads to the conclusion that the addition of fluoride is kinetically controlled. | en_US |
| dc.description | Results from theoretical calculations show that the more heavily substituted beta-substituted alkyl radical is not necessarily the more stable. Calculations for substituted alkanes suggest that alkyl substitution on the carbon bearing the functional group can have significant effects on the relative stability of these compounds. Studies involving the methoxy, fluoro, cyano and isocyano groups exhibit a correlation between the magnitude of this effect with the electron demand of the functional group. For the more electronegative substituents, stabilization by the alkyl groups on the carbon bearing the functional group becomes larger than on the carbon bearing the radical center, thus reversing the trend expected when considering radical stability alone. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1998. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Chemistry, Organic. | en_US |
| dc.subject | Chemistry, Physical. | en_US |
| dc.title | Factors influencing the regiochemistry of nucleophilic addition to the radical cation of alkenes and dienes studied in the context of the photochemical nucleophile-olefin combination, aromatic substitution (photo-NOCAS) reaction. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
