Hyperconjugation vs. apicophilicity in trigonal bipyramidal phosphorus species

Cramer, Christopher J.; Gustafson, Susan M.

doi:10.1021/ja00073a068

Cited by 23 publications

(26 citation statements)

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“…Alternatively, loss of the thiolate ligand may be facile from an equatorial position of TBP1 (path 2 in Scheme 2). Finally, apical elimination of thiolate from the alternative pseudorotamer TBP2 may proceed with a sufficiently low barrier that path 3 in Scheme 2 becomes the preferred process, even though in the absence of unusual hyperconjugative interactions, 45 one would expect TBP2 to be higher in energy than TBP1.…”

Section: Introductionmentioning

confidence: 99%

Molecular orbital calculations on the P?S bond cleavage step in the hydroperoxidolysis of nerve agent VX

Patterson

Cramer

1998

J. Phys. Org. Chem.

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The P-S bond cleavage process in the hydroperoxidolysis of a model system for the nerve agent VX was studied using ab initio and semiempirical molecular orbital methods. Aqueous solvation effects were included through single-point calculations using the semiempirical SM5.2PD/A continuum solvation model and geometries optimized at the HF/MIDI! level of theory. The predominant pathway for P-S bond cleavage involves pseudorotation of a low-energy trigonal bipyramidal intermediate followed by apical ligand ejection. In aqueous solution, the free energy barriers for these processes are found to be 14.3 and 4.6 kcal mol À1 , respectively, with electronic energies calculated at the MP2/cc-pVDZ//HF/MIDI! level of theory. By comparison with another continuum model of solvation (PCM), it is concluded that the SM5.2PD/A model performs well even for hypervalent phosphorus species, in spite of not having included any such molecules in the model's parameterization set.

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Section: Introductionmentioning

confidence: 99%

Molecular orbital calculations on the P?S bond cleavage step in the hydroperoxidolysis of nerve agent VX

Patterson

Cramer

1998

J. Phys. Org. Chem.

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“…20, No. 3, 2009 effects, the most electronegative substituents tend to occupy the apical positions in trigonal bipyramidal structures, 107,109,110 which would make them the preferable leaving groups. However, the possibility of occurrence of pseudorotations around the phosphorus atom and the possible existence of steric hindrances may result in a less electronegative group occupying an apical position in the intermediate, so becoming the preferable leaving group.…”

Section: Mechanism Of Action Of Opcsmentioning

confidence: 99%

“…However, the possibility of occurrence of pseudorotations around the phosphorus atom and the possible existence of steric hindrances may result in a less electronegative group occupying an apical position in the intermediate, so becoming the preferable leaving group. 106,110,111 So, breaking of a P-O or a P-S bond will be the result of a competition between the apicophilicity of the alcoxy group, kinetically favored, and the better stability as leaving group of the thioalkyl group, thermodynamically favored. 106,108,112 OPCs cause several deleterious effects in the organism, since ACh accumulation results in an excessive stimulation of nicotinic and muscarinic receptors in both central and peripheral nervous systems.…”

Section: Mechanism Of Action Of Opcsmentioning

confidence: 99%

Organophosphorus compounds as chemical warfare agents: a review

Delfino¹,

Ribeiro²,

Figueroa‐Villar³

2009

J. Braz. Chem. Soc.

226

178

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Os agentes de guerra química constituem uma das maiores ameaças do mundo moderno. Dentre estes, destacam-se os agentes neurotóxicos, em virtude de sua alta letalidade e periculosidade. Eles são compostos organofosforados que atuam pela inibição da enzima acetilcolinesterase, a qual é fundamental no processo de transmissão de impulsos nervosos. Existem várias formas de tratamento para a intoxicação por organofosforados, mas nenhuma delas é eficaz contra todos os agentes conhecidos ou contra todos os seus efeitos. Esta revisão tem como foco o uso de compostos organofosforados como agentes neurotóxicos de guerra química. Após uma breve introdução histórica, será feita uma discussão sobre as principais características estruturais e biológicas da acetilcolinesterase, seguida por uma revisão das propriedades dos compostos organofosforados e da sua aplicação como agentes de guerra química. Por fim, serão discutidas as formas de tratamento contra estes agentes, com ênfase nas oximas usadas para reativar a acetilcolinesterase inibida.Chemical warfare agents constitute one of the greatest threats in the modern world. Among them, the neurotoxic agents are of special interest due to their high lethality and danger. Neurotoxic agents are organophosphorus compounds that act by inhibiting the enzyme acetylcholinesterase, which is fundamental for the control of transmission of nervous impulses. There are several ways of treating intoxication by organophosphorus compounds, but none of them is efficient against all the known neurotoxic agents or against all of their effects. This review focus on the use of organophosphorus compounds as neurotoxic chemical warfare agents. After a brief historical introduction, it will be done a discussion about the structural and biological characteristics of acetylcholinesterase, followed by a review of the properties of organophosphorus compounds and their application as chemical warfare agents. Finally, the ways of treatment against intoxication with these agents will be discussed, with emphasis on the oximes used for reactivating the inhibited acetylcholinesterase.

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“…In general, the elimination of ligands from phosphoranes is more facile from apical positions than from equatorial. Stereochemistry in the phosphorane, i.e., the energetic preference for location of individual groups in apical or equatorial positions, is controlled by a number of factors, including apicophilicity and hyperconjugative interactions between the ligands [176] and solvation effects. Interconversion between different trigonal bipyramids requires a pseudorotation, and the barriers to pseudorotation in such complex phosphoranes are not well understood and may also be subject to solvation effects.…”

Section: Selected Applications In Environmental Chemistrymentioning

confidence: 99%

SMx Continuum Models for Condensed Phases

Cramer

Truhlar

2006

Trends and Perspectives in Modern Computational Science

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Abstract:The SMx continuum models are designed to include condensed-phase effects in classical and quantum mechanical electronic structure calculations and can also be used for calculating geometries and vibrational frequencies in condensed phases. Originally developed for homogeneous liquid solutions, the SMx models have seen substantial application to more complicated condensed phases as well, e.g., the airwater interface, soil, phospholipid membranes, and vapor pressures of crystals as well as liquids. Bulk electrostatics are accounted for via a generalized Born formalism, and other physical contributions to free energies of interaction between a solute and the surrounding condensed phase are modeled by environmentally sensitive atomic surface tensions associated with solute atoms having surface area exposed to the surrounding medium. The underlying framework of the models, including the charge models used for the electrostatics, and some of the models' most recent extensions are summarized in this report. In addition, selected applications to environmental chemistry problems are presented.

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Hyperconjugation vs. apicophilicity in trigonal bipyramidal phosphorus species

Cited by 23 publications

References 1 publication

Molecular orbital calculations on the P?S bond cleavage step in the hydroperoxidolysis of nerve agent VX

Molecular orbital calculations on the P?S bond cleavage step in the hydroperoxidolysis of nerve agent VX

Organophosphorus compounds as chemical warfare agents: a review

SMx Continuum Models for Condensed Phases

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