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|Title:||Dimerisation of nitrile oxides: a quantum-chemical study||Authors:||Pasinszki, Tibor
Westwood, Nicholas P. C.
|Issue Date:||2009||Publisher:||ROYAL SOC CHEMISTRY||Source:||PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 11(26). p. 5263-5272||Abstract:||The [3 + 2] and [3 + 3] cyclodimerisation processes of small nitrile oxides, XCNO (X = F, Cl, Br, CN, CH3) are investigated by ab initio coupled cluster theory at the CCSD, CCSD(T) and MR-AQCC levels for the first time. The favoured dimerisation process is a multi-step reaction to furoxans (1,2,5-oxadiazole-2-oxides) involving dinitrosoalkene-like intermediates with diradical character. The rate determining step for all but the F-species is the first, corresponding to the C-C bond formation. The kinetic energy barrier depends on the nature of the substituent X, generally increasing with decreasing electronegativity and increasing pi-donor ability of the substituent: F (Delta G(298) = 0 kJ mol(-1)) < Cl (72) < Br (90) < CH3 (104) < CN (114) (MR-AQCC(2,2)//UB3LYP/cc-pVTZ). Following initial C-C bond formation, three possible dinitrosoethylene diradical pathways are explored. Two of them are new, and one of them is a low-energy three-step path with implications for cycloreversion, tautomerism and detection of dinitrosoethylene intermediates. Alternative one-step, concerted [3 + 2] and [3 + 3] cyclodimerisation processes leading to 1,2,4-oxadiazole-4-oxides and 1,4,2,5-dioxadiazines have kinetic energy barriers around 100-240 kJ mol(-1) (CCSD//B3LYP), some 1.6 to 2.5 times higher than those leading to furoxans, supporting the experimental observations of furoxan formation as nitrile oxide loss channels during storage, trapping/re-vaporisation and reactions of nitrile oxides. Potential polymerisation initiation processes for NCCNO, involving the 1,2-dipolar NC substituent are also explored.||Notes:||[Pasinszki, Tibor] Lorand Eotvos Univ, Inst Chem, Dept Inorgan Chem, H-1117 Budapest, Hungary. [Hajgato, Balazs] Vrije Univ Brussels, B-1050 Brussels, Belgium. [Hajgato, Balazs] Hasselt Univ, Dept SBG, B-3590 Diepenbeek, Belgium. [Havasi, Balazs] Budapest Univ Technol & Econ, Dept Inorgan Chem, H-1521 Budapest, Hungary. [Westwood, Nicholas P. C.] Univ Guelph, Dept Chem, Guelph Waterloo Ctr Grad Work Chem, Guelph, ON N1G 2W1, Canada.||Document URI:||http://hdl.handle.net/1942/9804||ISSN:||1463-9076||e-ISSN:||1463-9084||DOI:||10.1039/b823406j||ISI #:||000267300000006||Category:||A1||Type:||Journal Contribution||Validations:||ecoom 2010|
|Appears in Collections:||Research publications|
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