AGRO 67 |
| Enantiomers and diastereomers are important classes of stereoisomers. Enantiomers are isomers that are related such that the object and its mirror image are not superimposable. Diastereomers are stereoisomers that differ in 3-dimensional arrangement and do not have the mirror-image relation. Diastereomerism arises out of differences in configuration or conformation. Enantiomers have identical physical and chemical properties, while diastereomers differ in physiochemical properties. Molecular descriptors derived from adjacency and distance matrices of molecular graphs fail in differentiating enantiomers because they have identical scalar properties. The same is true in the case of diastereomers arising out of polychiral diastereomerism. In such cases, we have to come up with new strategies to differentiate the three dimensional disposition of atoms around chiral centers. Molecular overlay of optimized geometries of diastereomers was found to be one of the possible alternatives because it is a holistic approach where the entire structures are compared rather than parts or descriptors calculated by reductionistic approaches. In order to find the level of theory necessary to get reasonable predictions, we used the quantum chemical methods in a graduated manner from semiempirical AM1, to Hartree Fock (STO3G, 3-21G, 6-31G, and 6-311G) to Density Functional Theory (B3LYP/6-31G, B3LYP/6-311G). We were able to correctly order the repellency of diastereomeric insect repellents using the hierarchical molecular overlay approach. |
|
New Developments and Issues in Agrochemical Sciences
8:00 AM-11:00 AM, Monday, August 20, 2007 BCEC -- Exhibit Hall - B2, Poster
Sci-Mix
Division of Agrochemicals |