Mechanisms, proposing

Attack on the electrophilic C-2 may occur as in the 2-aminothiazoles series, which probably explains the rearrangements observed in acidic medium (121, 711, 712, 723, 724), in aqueous medium with NaOAc (725), or with aqueous NaHCOj (725) (Scheme 232). That the initial attack probably involves the C-2 atom is substantiated by the fact that this rearrangement occurs under extremely mild conditions for 2-iinino-3-substituted-5-nitro-4-thiazolines (725). As the whole mechanism proposed (see p. 92) is reversible, when imino derivatives are submitted to such rearrangement conditions the rearrangement is expected to occur faster if steric interaction between 3- and 4-substituents exists in the 2-imino isomer. Another reaction may occur in acidic medium phenylimino-2-bipheny]-3,4-4-thiazoline hydrolyzed with hydrochloric acid gives the corresponding 4-thiazoline-2-one and aniline (717). 

The other mechanism proposes that the trichloride is formed by the further chlorination of the oxyhahde as ihustrated in equations 7—10 (13). 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

Novolaks produced from these catalysts exhibit a high content of 2,2 -methylene units. The mechanism proposed for the ortho-directing effect involves chelation of the phenoHc unit with the metal ion. 

In 1957 a procedure was described that selectively alkylated phenol in the ortho position (7). This approach, using aluminum catalysis, made a variety of 2,6-dialkylphenols accessible. The mechanism proposed for this ortho alkylation is outlined as follows ... 

The second mechanism, proposed by Mayo (116), involves the Diels-Alder reaction of two styrene molecules to form a reactive dimer (DH) followed by a molecular assisted homolysis between DH and another styrene molecule. 

Although the catalysis of the dimerization of aldehydes to acyloins by thiazolium ion has been known for some tlrae, the development of procedures using anhydrous solvents which give satisfactory yields of acyloins on a preparative scale was first realized in the submitters laboratories. The mechanism proposed by Breslow - for the thiazolium ion-catalyzed reactions is similar to the Lapworth mechanism for the benzoin condensation with a thiazolium ylide replacing the cyanide ion. Similar mechanisms are involved... 

A significant modification in the stereochemistry is observed when the double bond is conjugated with a group that can stabilize a carbocation intermediate. Most of the specific cases involve an aryl substituent. Examples of alkenes that give primarily syn addition are Z- and -l-phenylpropene, Z- and - -<-butylstyrene, l-phenyl-4-/-butylcyclohex-ene, and indene. The mechanism proposed for these additions features an ion pair as the key intermediate. Because of the greater stability of the carbocations in these molecules, concerted attack by halide ion is not required for complete carbon-hydrogen bond formation. If the ion pair formed by alkene protonation collapses to product faster than reorientation takes place, the result will be syn addition, since the proton and halide ion are initially on the same side of the molecule. 

Fig. 10. Growth mechanism proposed for the helical nanotubes (a) and helicity (b), and the model that gives the bridge and laminated tip structure (c).

In this paper Speziale and Smith 109) described experiments which led them to modify the mechanism proposed earlier 108) for the reaction of trivalent phosphorus compounds with haloamides. The first step is considered to be attack of the trivalent phosphorus compound on a chlorine atom of the halo amide (132) to produce a resonance-stabilized enolate ion (133). This is reasonable since under conditions where the trichloroamide... 

It is evident from the exceptions noted that the mechanism proposed above does not fully capture the pathways open to the Patemo-Biichi reaction. A great deal of effort has been devoted to deconvoluting all of the possible variants of the reaction. Reactions via singlet state carbonyls, charge-transfer paths, pre-singlet exciplexes, and full electron transfer paths have all been proposed. Unfortunately, their influence on product... 

There are no detailed reports on the mechanism of the Batcho-Leimgruber process. The mechanism proposed here is based on similar types of reactions reported in the literature. ... 

A number of reaction pathways have been proposed for the Fischer indolization reaction. The mechanism proposed by Robinson and Robinson in 1918, which was extended by Allen and Wilson in 1943 and interpreted in light of modem electronic theory by Carlin and Fischer in 1948 is now generally accepted. The mechanism consists of three stages (I) hydrazone-ene-hydrazine equilibrium (II) formation of the new C-C bond via a [3,3]-sigmatropic rearrangement (III) generation of the indole nucleus by loss of... 

The mechanism of the K-R reaction has been studied by several groups. " However, the mechanism proposed by Baker and Szell appears to be the most likely pathway. Szell and coworkers agreed with the original mechanism postulated by Baker based on product isolation, spectroscopy and kinetic studies. The o-hydroxyacetophenone 4 is first acylated... 

It was found inadvisable to use more than four molecules of form-amide [ (47) when R = H] per molecule of anthranilic acid and the condensation produces best results when the mixture is heated at 120 -130°C for 2 hr followed by further heating at 170°-180 C for 2 hr. Other variants of this reaction involve the use of ammonium o-acylaminobenzoates, anthranilic acid in the presence of nitriles and acetic anhydride, o-acetamidonitrile with acetic anhydride or hydrogen peroxide, anthranilic esters and aliphatic or aromatic amides or amidines, isatoic anhydride with amides or amidines, and anthranilic esters with aryl iminochlorides in acetoned The mechanism proposed by Bogert and Gotthelf has had experimental supporR and is represented in Scheme 12. 

Cava and Schlessinger have reported the synthesis of 1,2,3-triphenyl-isoindole (65) in 78% yield from 1,3-diphenylisobenzofuran (68) hy reaction with thionylaniline (69) and boron trifluoride. The mechanism proposed for this remarkable transformation involves reaiTangement of the adduct (70) derived from thionylaniline and the isobenzofuran, to the tricyclic intermediate (71). This presumably collapses to the S-sultam (72), which yields the isoindole (65) upon extrusion of sulfur dioxide. Loss of sulfur dioxide, both from S-sultones and unsaturated S-sultams, is well documented. ... 

There are two methods for the introduction of a hydroxyalkyl group at position 5 of the pyrazol-3-one ring. Schmidt and Zimmer converted furanediones 258a-k into arylmethylenepyrazol-3-reaction with hydrazine hydrate or methylhydrazine (83Jmechanism proposed for the reaction involves nucleophilic attack of the hydrazine on the ketone carbonyl, followed by attack on the ester carbonyl and ring opening of the... 

The mechanism proposed by Emmons thus corresponds in part to the decomposition of the trialkyl-oxaziranes by ferrous salts. By radical attack on the 7V-alkyl group of the oxazirane, the radical 32 is formed which rearranges with ring opening to 33. Radical 33 propagates the chain by attack on a further molecule of oxazirane. It takes up an H-atom and is decomposed to ketone and ammonia. The aldehyde produced from the M-alkyl group is converted to tar. 

The mechanism proposed for this abnormal reaction is illustrated by reference to the conversion of qumoxalin 3-one-2-carboxyanilide (48)... 

Formation of an intimate ion pair of OH " and aminium radical cation was also proposed for the intermediate step before deprotonation. The presence of the above radical was verified through UV analysis of the polymer formed with the characteristic band on the end group. Through chromatographic analysis of the TBH-DMT reaction products, H2O was detected as the above mechanism proposes after deprotonation. 

The polymers initiated by BP amines were found to contain about one amino end group per molecular chain. It is reasonable to consider that the combination of BP and such polymers will initiate further polymerization of vinyl monomers. We investigated the photopolymerization of MMA with BP-PMMA bearing an anilino end group as the initiation system and found an increase of the molecular weight from GPC and viscometrical measurement [91]. This system can also initiate the photopolymerization of AN to form a block copolymer, which was characterized by GPC, elemental analysis, and IR spectra. The mechanism proposed is as follows ... 

The results of Jamieson and McNeill cannot be accounted for by the intramolecular mechanism proposed by Grassie and coworkers [136,137] for the thermal degradation behavior of VC/VAc copolymers (Eqs, [28] and [29]). They can be accounted for much more convincingly by the alternative approach proposed by Naqvi based on polar interactions within the PVC matrix. Just like in copolymers even in blends, the polar carbonyl group of PVAc intensifies the concentration of like-poles in the PVC matrix resulting in destabilization. 

This technique is based in the fact that when cellulose is oxidized by ceric salts such as ceric ammonium nitrate Ce(NH4)2(N03)6 free radicals capable of initiating vinyl polymerization are formed on the cellulose. However, the possibility remains that the radical formed is an oxygen radical or that the radical is formed on the C-2 or C-3 instead of the C-6 carbon atom. Another mechanism, proposed by Livshits and coworkers [13], involves the oxidation of the glycolic portion of the an-hydroglucose unit. Several workers [14,15], however, have found evidence for the formation of some homopolymer. In the ceric ion method free radicals are first generated and are then capable of initiating the grafting process [16-18]. 

It is, however, more likely that the discrepancies observed in the periodate oxidation of malonaldehyde concern mainly the hydroxylation step. In the mechanism proposed (5) for this reaction, it is the enol form of malonaldehyde which is hydroxylated. However, titrations of a solution of malonaldehyde, prepared by hydrolysis of an aqueous solution (33) of carefully distilled 1, 3, 3-tri-ethoxypropene (46, 47), both with strong base and with iodine, indicate that only about 80% of the enol form is present in the equilibrium solution. On the other hand, the thio-barbituric acid test (58, 59) gave consistently higher values for the malonaldehyde content of the solution. The fact that only about 80% of the enol form is present in the equilibrium solution is all the more important as it can be shown (56) by titration with strong base that the enolization is slow, and moreover does not seem to go to completion. 

What evidence is there to support the carbocation mechanism proposed for the electrophilic addition reaction of alkenes One of the best pieces of evidence was discovered during the 1930s by F. C. Whitmore of the Pennsylvania State University, who found that structural rearrangements often occur during the reaction of HX with an alkene. For example, reaction of HC1 with 3-methyl-1-butene yields a substantial amount of 2-chloro-2-methylbutane in addition to the "expected" product, 2-chloro-3-methylbutane. 

It is highly probable that the monomer is first coordinated onto a vacant position of the complex and then pushed between a boron-carbon bond of the catalyst. The following mechanism, proposed by Bawn, can be considered as a prototype of coordinated complex polymerization ... 

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