Postulated formation

The following mechanism for the reaction has been suggested. It postulates formation of an intermediate paraconic ester (A) the irreversible alkoxlde cleavage of this cyclic ester drives the reaction to completion ... 

The question as to whether a flame retardant operates mainly by a condensed-phase mechanism or mainly by a vapor-phase mechanism is especially comphcated in the case of the haloalkyl phosphoms esters. A number of these compounds can volatilize undecomposed or undergo some thermal degradation to release volatile halogenated hydrocarbons (37). The intact compounds or these halogenated hydrocarbons are plausible flame inhibitors. At the same time, thek phosphoms content may remain at least in part as relatively nonvolatile phosphoms acids which are plausible condensed-phase flame retardants (38). There is no evidence for the occasionally postulated formation of phosphoms haUdes. Some evidence has been presented that the endothermic vaporization and heat capacity of the intact chloroalkyl phosphates may be a main part of thek action (39,40). 

Some remarkable chemistry is observed when silenes react with heteroatom systems, in particular carbonyl compounds (]>C=0) and imines Q>C=N—R). The reaction with ketones was first described by Sommer (203), who postulated formation of an intermediate siloxetane which could not be observed and hence was considered to be unstable even at room temperature, decomposing spontaneously to a silanone (normally isolated as its trimer and other oligomers) and the observed alkene [Eq. (14)]. Many efforts have been made to demonstrate the existence of the siloxetane, but it is only very recently that claims have been advanced for the isolation of this species. In one case (86) an alternative formulation for the product obtained has been advanced (204). In a second case (121) involving reaction of a highly hindered silene with cyclopentadienones,... 

Oae and Numata26 were the first to postulate formation of a disulfonium dication in reaction of concentrated sulfuric acid with monosulfoxide of a bis-sulfide. Later Furukawa et al.62 found that the crystalline hydrosulfate 36 can be prepared by reaction of the corresponding monosulfoxide 13 (or A-tosyli-mide 14) with concentrated sulfuric acid. Formation of a symmetric dication 38 was confirmed by isolation of 1 1 mixture of deuterated sulfoxides 37 and 39... 

Following a report by Biichi and Ayer > on the photolysis of nitrobenzene in cyclohexene and 2-methyl-2-butene, a thorough study on nitrobenzene cycloaddition to olefines has been undertaken by de Mayo and co-workers 3 . ). Evidence was presented for the previously postulated ) formation of 1,3,2-dioxazolidines ... 

Figure 1. Postulated formation of a-dialkylamino nitrite esters (I) from immo-nium ion donors and their fragmentation to nitrosamines...

A second requirement of the Tronov postulates—formation of acid anhydrides—is met by evidence from infrared spectra of oxidized coal samples periodically withdrawn from the reactor. As a matter of experimental record, it should be observed that such anhydrides did not appear until the later stages of reaction, by which time -COOH concentrations were already quite high. However, since initial carboxyl formation probably occurs in aliphatic structures present in the parent coal (9), appearance of anhydrides after rather... 

Corey has made a study of the relative reactivities of various olefins to attack by excited cyclohexenone and has concluded that the excited state is an electrophilic reagent.420 This fact has led him to postulate formation of a charge-transfer complex between excited... 

A mechanism postulating formation of a carbocation as an intermediate during oxidative fluorination of the C=C bond was proposed for the reaction of CoF3 with F-benzene and F-pyridine [32], and VF5 with fluoroolefins and polyfluoroaromatic compounds [33] ... 

Figure 10. Postulated formation of C20 isoprenoid thiophenes and bithiophenes by incorporation of sulfur into phytenes. Different substrates lead to different thiophenes which is the major control for the thiophene ratio.

The same reaction, originating from the non-fluorinated compound (i.e. ethylammonium chloride) yields the borazine after refluxing for only 15 to 20 hours in the same solvent. The postulated formation of [CF3CH2NBC1]3 69> could not be confirmed 64>. However, 2,4,6-organo-and fluoroorgano-substitituted derivatives of l,3,5-tris(trifluoroethyl) borazine have been made from [CF3CH2NBC1]3 by Grignardalkyla-tions 64>. 

Gillespie Mid GrahMn [42] have carried out a cryometric exMnination of solutions of nitric acid in oleum. The results obtained Me in agreement with the following equation, postulating formation of the nitronium ion ... 

Fig. 4.4. Scheme for postulated formation of the tyrosine phenoxyl and peroxyl radical... 

Scheme 10.4 Postulated formation of pyrrole and 2-aminoimidazolinone moieties.

Figure 5. Postulated formation of wine-lactone 10 from monoterpenoid acid 9A in analogy to dillether 12 formation from the structurally related chol 11.

Other mechanistic studies on carbonyl insertions of molybdenum(II) complexes, RMo(f7 -C5H5)(CO)3, postulated formation of an acyl intermediate stabilized by interaction of the hydrocarbon portion of the acyl group with the metal, similar to the well-established agostic interaction). 

The substantial acceleration of radical ion formation observed in the homolysis of peroxide bonds in orf/zo-substituted sulfenyl perbenzoates, e.g. (41), is in agreement with the postulated formation of bridged radicals (42) (Figure 7). 

DTA maxima for the cis and trans forms of [Co(NH3)2Cl2] were at 507 and 500 K, respectively, and for the dissociation of the monoammine compound was 559 K. These observations confirm that the cobalt(II) compounds are less stable than those of cobalt(III), which is consistent with the postulated formation of cobalt(II) compounds as unstable intermediates in those decompositions of cobalt(III) compounds which are initiated by an electron transfer step. 

An alternative mechanism has been suggested [13] which postulates formation of ion pair directly from the 1,2-diiodo compound and/or its reaction with I2 ... 

However, several questions remain to be answered (1) Is the postulated formation of an acylperoxo-iron(III) complex correct (2) If the answer is yes, how can it be proved (3) Does the peroxo-iron(III) porphyrin complex afford an oxoferryl porphyrin cation radical Recently such an acylperoxo-iron(III) porphyrin complex (16) in solution at low temperature has been directly observed and characterized (78). It was found that 16 did indeed react to yield the oxoferryl porphyrin cation radical 14. 

W. M. Meier (Eidgenossische Technische Hochschule, Zurich) In connection with the postulated formation of a surface methoxy species on heating TTMA-Y, it might be of interest to note that we have observed pronounced methyl-oxygen interaction in the structures of TTMA-soda-lite and TTMA-gismondine (C. Baerlocher and W. M. Meier, Helv. Chim. Acta 1969, 52, 1853, and in press). 

This enzyme activates the simplest of all substrates and causes the parahydrogen conversion and hydrogen deuteride reaction. Krasna and Rittenberg (26, 27) have postulated formation of an enzyme hydride EH,... 

Ion pair. This hypothesis postulates formation of a tightly bound ion pair of zero charge. The eluant pH is adjusted as previously described and then an IPR containing a counter-ion (A ), which has the opposite charge to that of the compounds to be determined, is added to the sample and... 

An alternative mechanism can be proposed which is based on the derivation, in Chapter 2, of the rate of termolecular collisions. This derivation postulated formation of an unstable complex between two of the atoms and subsequent collision of the complex with the third body. This mechanism can be described by... 

The postulated formation of the polynuclear peroxo intermediate has precedence in the literature of Fe(II)-porphyrin systems. In addition, the only structurally characterized non-heme iron(ni) peroxide complex, [Fe6(02)C>2(0Bz)i2] (5), has a structural motif similar to that in the key intermediate, namely, a p,p- n2, q2-peroxide spedes in which four ferric ions are coordinated to the peroxide dianion (I3 in Scheme 1). Because 5 has all ferric ions, this peroxide-bridged complex is stable. The species in Scheme 1, on the other hand, is mixed-valent Fe 2F 2/ and can therefore decompose by redox chemistry to form the stable (p-oxo)diiron(ni) product. 

Table 3.56). An explanation was put forward by postulated formation of Ji-complex of cuprous chelate which coordinates to aryl halide could be affected by nitro group drawing electron density from the benzene moiety.

It is interesting that in neither Durie s work nor the studies of Birks et al. is there any requirement to postulate formation of excited 11 states of IF by radiative recomlnnation of atoms. 

As an extension of hydrosilylation of alkenes, cyclization-hydrosilylation of 1,6-dienes occurs by the reaction with HSiRs [23]. The cationic complex 37, generated in situ from (phen)Pd(Me)Cl and NaBAr4, is an active catalyst, catalyzing the reaction of dimethyl diallylmalonate (36) with HSiCl3 to give the disubstituted cyclopentane 38 with 98% trans selectivity in 92% yield [24]. A mechanism different from that of usual hydrosilylation, which postulates formation of H-Pd-SiR3 and hydropalladation of alkene, was proposed by Widenhoefer... 

For the system wool-water a theory of this kind has been developed by Cassie and in a particularly interesting paper by Hailwood and Horrobin The latter postulated formation of a monohydrate, i. e., binding of one water molecule by each monomeric residue of the fibre portion taking part in absorption. For the isotherm they gave the equation ... 

Similarly to the biosynthesis of lipoxins and E-resolvins, the postulated formation of D-resolvins [15] takes place from DHA and involves similar dual lipoxy-genations (Figure 9.5). The action of 15-LO on DHA forms 17S-HpDHA followed... 

In 1944, Roedel from DuPont postulated formation of SCB via intramolecular chain transfer, which reduced crystallinity, density, modulus, and solubility... 

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