ORGN 422 |
| San-Yan Chu, Department of Chemistry, National Tsing Hua University, Hsinchu, 30013, Taiwan and Yi Ren, Faculty of Chemistry, Sichuan University, Sichuan,P.R.C, Chengdu, 610064, China. |
| Identity ion pair SN2 reactions LiX + CH3X ®XCH3 + LiX (X=F, Cl, Br and I) were investigated at the level of modified Gaussian-2 theory. Two possible reaction mechanism, inversion and retention, were discussed. The reaction barriers relative to the free reactants (DH) for inversion mechanism are found to lie within a large range, decreasing in the following order: F(204.7 kJ/mol) > Cl(146.9 kJ/mol) > Br(119.0kJ/mol) > I(97.3 kJ/mol). The barrier gap between the two mechanism [DH(ret) -DH(inv)] increase in the order F(-62.6 kJ/mol) < Cl( 4.4 kJ/mol) < Br(24.8 kJ/mol) < I(45.1 kJ/mol). Thus the retention mechanism is energetically favorable for fluorine and the inversion mechanism is favored for other halogens. Good correlation between DH for inversion pathway with the looseness of inversion transition state %C-X, the dissociation energies of C-X bond (DC-X) and Li-X bond (DLi-X), respectively, are observed.
|
|
Physical Organic, Materials, Heterocycles, Aromatics, Metal-Mediated Reactions
8:00 PM-10:00 PM, Tuesday, September 9, 2003 Hilton New York -- Americas Hall 1, Poster
Division of Organic Chemistry |