4<i>H</i>‐1,2‐Oxazet‐<i>N</i>‐oxide aus 1,1‐Di‐tert.‐butylallenen

Wieser, Karlheinz; Berndt, A.

doi:10.1002/ange.19750870211

Cited by 10 publications

(2 citation statements)

References 3 publications

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“…Although formation of VII in thermal decomposition of nitroethylene was not proved experimentally, related oxazetes were prepared by cyclization of substituted nitroethylenes [29,30].…”

Section: Radical Decompositionmentioning

confidence: 99%

Mechanism of gas-phase decomposition of nitroethylene: A theoretical study

2004

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Calculations by the B3LYP density functional method with various basis sets and by the QCISD(T)/6-31G(d) ab initio method showed that the main pathway of monomolecular gas-phase decomposition of nitroethylene is that involving a cyclic intermediate, 4H-1,2-oxazete 2-oxide; the barrier of its formation (201.9, 203.9, and 216.5 kJ mol !1 , as estimated by various methods) reasonably agrees with the experimental value (191.9 kJ mol !1 ). The barriers of alternative pathways of gas-phase decomposition of nitroethylene are considerably higher. The barriers of reactions involving radical cations are considerably lower than those of the similar reactions involving molecules. Among all the considered pathways of nitroethylene decomposition, bimolecular pathways are the most favorable energetically.Two major pathways of gas-phase decomposition of aliphatic nitro compounds have been proved experimentally: homolytic cleavage of the C3N bond with generation of free radicals and elimination of HNO 2 [13 4]. The molecular mechanism is realized at relatively low temperatures (up to 350oC) with mononitroalkanes containing a hydrogen atom in the a position relative to the nitro group, and also with halonitroalkanes RCH 2 CHXNO 2 (X = Hlg) [2, 3]. Gasphase decomposition of nitroethylene I and other a-nitroolefins is presumed to occur by a similar mechanism [2, 3, 5]. For mononitroalkanes, the molecular mechanism of HNO 2 elimination is confirmed by data on the composition of products in the initial steps of decomposition [1,2] and by the results of quantumchemical calculations [6 38]. Data on the composition of products formed in the initial steps of decomposition of I are lacking; therefore, the molecular mechanism for this compound is just a hypothesis. Published results of quantum-chemical studies of nitroethylene decomposition [9,10] are apparently insufficient to make any definite conclusions on the primary step of the monomolecular gas-phase decomposition or to cast doubt on the suggested pathway of HNO 2 elimination. In [11,12], we found that the barrier to elimination of HNO 2 from a molecule of I [223.9 kJ mol !1 according to B3LYP/6-311++G(df,p) calculations] significantly exceeds the experimental activation energy of the gas-phase decomposition (191.9 kJ mol !1 ).In this work, we studied theoretically various alternative pathways of monomolecular decomposition of

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“…Although formation of VII in thermal decomposition of nitroethylene was not proved experimentally, related oxazetes were prepared by cyclization of substituted nitroethylenes [29,30].…”

Section: Radical Decompositionmentioning

confidence: 99%

Mechanism of gas-phase decomposition of nitroethylene: A theoretical study

2004

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“…Monomeric nitrosoolefins can be isolated only in the absence of strong nucleophiles and if their structure makes both a rearrangement and a polymerisation impossible. So we succeeded in the preparation of three 2,6disubstituted 1-phenyl-2-nitroso prop 1-enes [4], and later the isolations of 1-nitroso 2,2-di-tert-butyl ethylene [5] and 1,ldichloro-2-nitroso prop-1-ene [6] were also accomplished.…”

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confidence: 99%

Structure of monomeric 1-aryl-2-nitroso-prop-1-enes

Engel

Pritzkow

Gelbrich³

et al. 1995

J. Prakt. Chem.

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Nitrosoolefins are unstable intermediates in nucleoplilic substitutions at bischloronitroso compounds and a-chlorooximes [ l -31. They react rapidly with nucleophilic agents; in the absence of such agents they rearrange by a proton shift to oximes of &$-unsaturated carbonyl compounds. A further possible reaction of monomeric nitrosolefins is the polymerisation to tarry compounds. Monomeric nitrosoolefins can be isolated only in the absence of strong nucleophiles and if their structure makes both a rearrangement and a polymerisation impossible. So we succeeded in the preparation of three 2,6disubstituted 1-phenyl-2-nitroso prop 1-enes [4], and later the isolations of 1-nitroso 2,2-di-tert-butyl ethylene [5] and 1,ldichloro-2-nitroso prop-1-ene [6] were also accomplished.In our earlier work [4] we did not succeed in determining the configuration of the 1-aryl-2-nitroso prop-1-enes prepared, and it remained uncertain whether a stabilization of the compounds by mesomerism of the nitroso olefin group with the aromatic nucleus takes place. The position and the extinction coefficient of the n-r* band in the region of about 700 nm seemed to be arguments for a stabilization of these nitrosoolefins by mesomerism with the aromatic nucleus. On the other hand the substituents in 2-and 6-position of the phenyl group make a coplanar arrangement of the aromatic ring and the nitrosolefin system very improbable.We have once again prepared the nitrosoolefins lbd described in [4] and moreover 1-(2,6-dimethylphenyI)-2nitroso prop-1-ene l a in order to elucidate their structure by X-ray analysis. Only in the case of 1-(2-methoxy-4,6-1 Formula Scheme 1 Structure of 1-(2-methoxy-4,6-dimethylphenyl)-2-nitroso prop-1-ene Id. The plane of the nitrosoolefin side chain is twisted out of the plane of the aromatic nucleus with an angle of (49.3 i 0.2)". Table 1 13C-and 'H-nmr signals of the nitrosoolefins la-d Ar\ /CH3 1 b Ar : 2,4,64rirnethylphenyI

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