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|Title:||Theoretical studies of thermal syn elimination reactions|
|Author(s):||Erickson, Jon A.|
|Doctoral Committee Chair(s):||Kahn, Scott D.|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||An ab initio molecular orbital study of two classes of thermal syn elimination reactions was undertaken in order to provide insight into the mechanism of these reactions. In general, thermal syn elimination reactions involve a one step process with a cyclic transition structure. The first class studied is termed 1,5 thermal eliminations and involve a six-membered ring transition structure. In particular, the reactants, transition structures and product geometries of the ethyl formate, phosphinate, and xanthate were optimized at the RHF/6-31G* level. In addition, MP2/6-31G* energies and RHF/6-31G* electrostatic potentials were calculated. Trends in calculated activation energies and electrostatic potentials agree with experimental results. It was determined that the C$\sb\alpha$-O bond appears to be breaking first in the reaction. It was also found that the effect of polar substituents agree with experimental results. Electron withdrawing groups in the $\beta$ position were found to change the order of bond breaking to C$\sb\beta$-H bond dissociation while $\alpha$ electron donating groups significantly increase the C$\sb\alpha$-O bond length in the transition structure.
The second class of elimination reactions involves those which go through a five-membered ring transition structure and are termed 1,4 thermal eliminations. These reactions were studied in a similar manner as the 1,5 class. The reactions examined were the thermal eliminations of amine oxides, sulfoxides, selenoxides and telluroxides at the RHF/6-31G* and/or the RHF/3-21G(*) levels. Again the calculated activation energies and electrostatic potential agreed with experimental observations. Unfortunately, rate trends did not correlate with transition structure properties. It was found, however, that polar substituents had the same effect on the transition structures as in the six-membered ring transition structure class.
|Rights Information:||Copyright 1992 Erickson, Jon A.|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9236452|