Fragmentation spontaneous

Optical emission is a result of electron impact excitation or dissociation, or ion impact. As an example, the SiH radical is formed by electron impact on silane, which yields an excited or superexcited silane molecule (e + SiHa SiH -t-e ). The excess energy in SiH is released into the fragments SiH SiH -I-H2 + H. The excited SiH fragments spontaneously release their excess energy by emitting a photon at a wavelength around 414 nm. the bluish color of the silane discharge. In addition, the emission lines from Si. H, and H have also been observed at 288, 656, and 602 nm, respectively. 

Nitrile imines generated by the benzaldehyde phenylhydrazone-chloramine-T route have been added to 1-azetines (219) (X = 0, S) (95,124). However, the adducts 220 (X=0, S) proved to be less stable than those derived from nitrile ylides (186) (94) and in many cases fragmented spontaneously to give the 5-butenyl-1,2,4-triazoles (221) as the isolated products. It was found, however, that... 

There are two mechanisms which allow a radical to react in situations where the parent molecule is inert. First, the reaction between a surface and parent molecule may be exothermic but require a large activation energy to proceed. (This is probably the case for methane which is very unreactive toward a large variety of clean surfaces .) When the activation energy is provided by dissociating the molecule while it is in the gas phase, then the resulting fragments spontaneously react with the surface. 

Finally, because very low temperamres are needed to solidify the above host gases, reactive intermediates may be generated under conditions where unimolecu-lar thermally activated processes are also largely suppressed, unless they involve quantum mechanical mnneling. Thus, species that rearrange or fragment spontaneously even at 77 K can be stabilized, say, at 10 K, provided that such processes are not driven by excess energy that is imparted onto the incipient intermediates on their formation by photolysis or radiolysis (see below). 

Silicon-induced fragmentations.2 Treatment of the tetrahydropyridinium salt 1 with CsF in CH3CN results in a stereoselective fragmentation to the (2Z,5E)-heptadiene 2. In contrast, the N-oxide 3 fragments spontaneously to the (Z,Z)-heptadiene 4. This fragmentation has been used to obtain (E,E)- and (E.Z)-dienes.3... 

Anhydro-4-hydroxyoxazoIium hydroxides, such as compound (231), behave as carbonyl ylides (232) in cycloaddition reactions, yielding bicyclic adducts with alkenes and carbonyl compounds (Scheme 24). The adducts produced by combination with alkynes fragment spontaneously in a retro-Diels-Alder reaction, giving furans (equation 57). The formation of a furan by the action of DMAD on the 4(5//)-oxazolone (233) shows that the latter exists in equilibrium with the mesoionic tautomer (234 equation 58) (79JOC626). 

Metastable ion ion that fragments spontaneously in a field-free region. 

Fragmentation ofphosphoranes. 3-Mcthyl-l-phcnyl-3-phospholene (I) reacts with diethyl peroxide to give the phosphorane (2). which fragments spontaneously at room temperature to give isoprene (3) and diethyl phcnylphosphonite (4). 

It is common practice not to show the weak base that removes H+, so that the carbocation seems to fragment spontaneously. 

Dehalogenation of a-halo ketones. a-Halo ketones can be dehalogenated by treatment with pyridine in acetone followed by addition of sodium hydrosulfite yield 50-75%. The method involves formation of a pyridinium salt, which is then reduced in acetic acid to a 1,4-dihydropyridine derivative this fragments spontaneously to the ketone and pyridine. ... 

Plaza-Compounds. The criss-cross cycloaddition of JN-phenylmaleimide to benzal-dehyde azine, PhCH=NN CHPh, results in the pyrazolopyrazole-derivative (485) 432 hexafluoroacetone azine and ethyl acrylate or ethyl vinyl ether similarly yield the [l + 2] adducts (486 R = COOEt or OEt, respectively).433 — Compound (487) opens to the ylide (488) on heating in the presence of tetracyanoethylene the 4 + 2 ] cycloadduct (489) is formed, which fragments spontaneously to the beta-ine (490) and the diene (F,C),OCHCH-C(CN),. Thermolysis of the diazabicyclo-... 

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