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Authors: Nguyen, Minh Tho ×
Issue Date: 1994
Series Title: Journal of the Chemical Society. Faraday transactions vol:90 issue:12 pages:1771-1781
Abstract: Ab initio molecular orbital calculations have been used to explore the C2H5P potential-energy surface. Geometries were optimized at the MP2/6-31G(d,p) level while relative energies were estimated using QCISD(T)/6-311G(d,p) calculations and corrected for zero-point energies. Among C2H5P isomers, phosphirane 1, vinylphosphine, 2, 1-phosphapropene, 3, and 2-phosphapropene, 9, are low-energy isomers and have similar energy content. 1 lies only 5 kJ mol-1 above the most stable isomer, 9. This is in line with the experimentally observed equilibrium between substituted phosphiranes and vinylphosphines. The 1-2 rearrangement is a single-step process with an energy barrier of 235 kJ mol-1, which is not inconsistent with experimental thermal reactions at 500-degrees-C. The 1-3 interconversion seems possible via ethylphosphinidene, 5, but 5 is not an equilibrium structure. The 2-3 isomerization is possible via either an antarafacial or a suprafacial 1,3-hydrogen shift with a barrier height of ca. 263 kJ mol-1. This represents the first example of an accessible suprafacial 1,3-hydrogen shift. The 1,3-hydrogen shift in 2-phosphapropene remains an antarafacial mode with an energy barrier of 288 kJ mol-1 (in comparison with 345 kJ mol-1 in propene). Phosphinoethylidene, 4, is a high-energy isomer lying 201 kJ mol-1 above 1 and separated from 2 and 3 by moderate energy barriers (61 and 58 kJ mol-1). 4 is not involved in interconversions of 1, 2 and 3. While 1,2-H, loss from 3 giving CH3-C=P or CH2=C=PH is unlikely, cycloreversion of 1 giving an alkene plus a phosphinidene is a realistic thermal process and thereby a possible mechanism for the formation of CH3-C-P upon thermolysis of vinylphosphirane at 700-degrees-C. Conversion of phosphirane to 9 is possible by two distinct two-step pathways: the first involves (methylphosphino)methylene, 8, as an intermediate whereas the second pathway involves bis(methylene)phosphorane, 10. The latter is favoured over the former. Overall, these ring-chain isomerizations of phosphirane constitute a novel type of reaction of phosphorus compounds which do not exist in either carbon or nitrogen analogues.
ISSN: 0956-5000
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Quantum Chemistry and Physical Chemistry Section
× corresponding author
# (joint) last author

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