2007 Student Research Conference:
20th Annual Student Research Conference

Science

3-D Molecular Structures of Organophosphorus Pesticides as Determined by X-Ray Diffraction
Gabriel B. Hall
Dr. Russell G. Baughman, Faculty Mentor

As part of a summer undergraduate research program (STEP), and funded by the National Science Foundation, the crystal and three-dimensional structures of three organophosphorus compounds were determined by X-ray diffraction. The pesticide of primary interest is 2-(di-ethoxy-thiophosphoryloxy)-7-methyl-pyrazole[1,5-α]pyrimidine-6-carboxylic acid ethyl ester (Pyrazophos) C14H20N3O5PS, a systemic fungicide. Pyrazophos exhibits 2 rotamers per asymmetric unit, and a carbonyl···ring π system interaction between the carbonyl oxygen and the ring center. This interaction occurs along the b-axis and is present in only one rotamer. Of note is a discrepancy between the observed placement of a ring methyl position and the placement as seen in the current literature. O-2,6-dichloro-p-Tolyl O,O-dimethylphosphorothioate (also known as Tolclofos-Methyl) C9H11Cl2O3PS, was also determined during the program, and of interest in this compound is libration about the central phosphorus atom resulting in partial occupancies of the two methoxy groups. Structural similarities to Tolclophos-Methyl are noted in the insecticide Dicapthon (O,O-dimethyl-O-(2-chloro-4-nitrophenyl)phosphorothioate, C8H9ClNO5PS).

Keywords: Crystal Structure, Pesticide, Organophosphorus, Insecticide, Fungicide, X-ray Structure, Single Crystal, Cholinesterase

Topic(s):Chemistry

Presentation Type: Poster

Session: 8-4
Location: OP Lobby
Time: 4:15 pm

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