Keerthi Jayasuriya

Computational analysis of some properties associated with the nitro groups in polynitroaromatic molecules

Abstract It is shown, for a group of polynitroaromatic compounds, that the measured impact and shock sensitivities correlate well with the electrostatic potential at the midpoint of the longest CNO 2 bond, as calculated from the carbon and nitrogen atomic charges. The latter were computed from ab initio SCF wavefunctions, based upon crystallographically determined molecular geometries. The SCF orbital energies support an earlier assignment of the two peaks corresponding to the 1s electrons of the NO 2 nitrogens in the X-ray photoelectron spectra of several of these compounds. The main peaks are believed to be those at the lower binding energies, with satellites at the higher energies.

[1.1.1]Propellane, bicyclo[1.1.1]pentane and the effects of “inverted” carbons

Abstract The stabilities and reactive properties of [1.1.1]propellane and bicyclo[1.1.1]pentane are analyzed by means of calculated electrostatic potentials and bond deviation indices. These were computed from ab initio SCF minimum-basis-set molecular wave functions, using geometries determined by optimization at the 6-31G* level. [1.1.1] Propellane has rather unusual regions of relatively strong negative electrostatic potential to the outsides of the bridgehead carbons, those commonly described as “inverted”. These carbons are viewed here as being somewhat unsaturated, with no direct bonding between them. They should be attractive sites for electrophilic attack, and it is suggested that they may also be reactive toward radicals. Bicyclo[1.1.1]pentane has a less strained structure, and the electrostatic potentials and bond deviation indices reveal the CC bonds to have some similarity to those in cubane.

A computational analysis and comparison of some sarin and soman analogues

Abstract Several analogues of sarin ( I ) and soman ( II ) were investigated for their possible ability to elicit effective antibodies to these anti-cholinesterase agents. The key issue is whether the fluorines in sarin and soman can be replaced by some other functional group that would result in lower toxicity, so that antibodies would have the opportunity to form, but that mimics fluorine well enough that these antibodies would also show satisfactory anti-sarin and anti-soman activities. The analysis involved a comparison of calculated (ab initio SCF) electrostatic potentials of five molecules; one ( IV ) serves as a sarin/soman model, while in the others the —F was replaced by a group X, where X = —CN, —OH, —OCH 3 or —NH 2 . On the basis of the electrostatic potential analysis, it was concluded that —CN and —OCH 3 show the greatest promise, for present purposes, as fluorine replacements.

A study of the reactive properties of a VX model compound, as determined by electrostatic potential calculations

Abstract An ab initio self-consistent-field approach has been used to study the properties of an organophosphorus compound which is being taken as a model for VX ( O -ethyl- S -2-diisopropylaminoethyl methylphosphonothiolate). The optimized geometry was determined at the STO-3G* level, and an STO-5G basis set was then used for computing the molecular electrostatic potential. This shows major negative regions (attractive toward electrophiles) near the phosphoryl oxygen and the nitrogen, with increasingly weaker ones in the vicinity of the alkoxy oxygen and the sulfur. It is suggested that an essential factor in the anticholinesterase activity of VX may be the presence of negative potentials of appropriate magnitudes associated with the oxygens and the sulfur. Our results support earlier speculation that the presence of the nitrogen may interfere with the metal-catalyzed hydrolysis of VX.