Activation energy oxetane

It can be concluded that the [3+2] pathway seems to be the only feasible reaction pathway for the dihydroxylation by permanganate. The study on the free activation energies for the oxidation of a. P unsaturated carboxylic acids by permanganate shows that the [3+2] mechanism is in better agreement with experimental data than the [2+2] pathway. Experimentally determined kinetic isotope effects for cinnamic acid are in good agreement with calculated isotope effects for the [3+2] pathway, therefore it can be concluded that a pathway via an oxetane intermediate is not feasible. 

CPCM) solvation, to study the mechanisms and stereochemistries of this important synthetic reaction. Interestingly, from these calculations, it was concluded that secondary enamine-mediated aldols have high activation energies if there is no proton source, and oxetane intermediates such as 1 can be formed (Equation 1) <2001JA11273>. 

The Woodward-Hoffmann rules predict high activation energies for the suprafacial-suprafacial addition of two carbon-carbon double bonds, which can be lowered, however, by polar effects. [2 + 2] Photocycloadditions are common and usually involve diradical intermediates e.g., photoexcited ketones react with a variety of unsaturated systems (Scheme 1). Both the singlet and triplet (n, 7t ) excited states of the ketones will form oxetanes with electron-rich alkenes. With electron-deficient alkenes only the singlet states give oxetanes. Diradicals are the immediate precursors to the oxetanes in all cases, but the diradicals are formed by different mechanisms, depending on the availability of electrons in the two components. 

Acetaldehyde, 119-20, 380-82 Acetone, chemical titration. 428 oxetane formation, 318, 427 singlet and triplet states, 382. 428 Acetophenone. 407. 467 Acetylene, 203. 348 cycloaddition, 415, 423 excited state geometry. 45-46 2-Acetylnaphthalene, 398 6-Acetyloxycyclohexadienones. 463 Acidity, excited states, 48-52 Acrolein, 34, 382-83, 433 Acrylonitrile, 328, 414-15, 417 Activation energy, 382-83, 400 Acyl radical. 3S2-S5, 380-82, 460 Adiabatic. See Potential energy surface ... 

Mill and Montorsi [38], in a more detailed kinetic study, showed that, not only was intramolecular abstraction the dominant process, but the ratio of rates of intra- and intermolecular abstraction was almost unchanged with temperature indicating little (<1 kcal mole-1), if any, difference in activation energy between the two steps. Moreover, at very low oxygen concentrations, some oxetane formed by ring closure of I in competition with (the much faster) addition of oxygen, viz. 

A computational study of the concerted C(sp )-0 reductive elimination of olefin oxides from complexes 19a and 19b showed that the Gibbs activation energy of epoxide elimination increases in the following order of 19a 19b 20 [33]. In other words, migration of a secondary aUcyl from the Pt center to the oxetane oxygen atom is a more facile process than that involving a primary alkyl group. 

The calculations of the transition states led to the following predictions concerning the kinetically most favorable reactions pathways [140]. The reaction of ketene with OSO4 should proceed via [3+2] addition across the C=C bond. The [2+2] addition reactions of all LReOj species to ketene have lower activation energies than the [3+2] addition. These were the first examples where calculations showed that the [2+2] addition of a metal oxide to a C=C bond has a lower barrier than the [3+2] addition. For Re07 and (HjPNlReOj it was found that the [2+2] addition to the C=0 bond is kinetically even more favorable than the addition to the C=C bond. However, the calculation predicted that the [2+2] addition of MeReOj, CpReOj and Cp ReOj should proceed via [2+2] addition across the C=C bond yielding the metalla-2-oxetane. 

The activation energy of polymerizations of oxetane monomers is higher that that of tetrahy-drofuran (see next section). This indicates that the orientation of the cyclic oxonium ion and the monomer is looser in the Siv2 transition state" ... 

The role of formaldehyde dimer in 0-containing heterocycles formation by the Prins reaction have been investigated. It was shown that the 1,3-di-oxanes, hydrogenated pyrans and oxetanes can be can be obtained from formaldehyde dimers and alkenes in the gas phase. The activation energy of these reactions is different. It is lower for 1,3-dioxanes formation, and higher for oxetanes formation. Thus formation of 1,3-dioxanes happens in the conditions of kinetic control. Opposite, the hydrogenated pyrans formation happens in the conditions of thermodynamic control... 

Thus, according to the calculated data, hydrogenated pyrans and oxetanes are possible to be formed along with the formation of alkyl-substituted 1,3-dioxanes in the reaction of FD with alkenes. In this case the formation of 1,3-dioxanes is characterized by lower activation energy... 

The most extensively used source of trifluoromethyl radicals is the photolysis of hexafluoroacetone. The primary process has been investigated in some detail by Kutschke and co-workers. Two mechanisms of photolysis were observed, one from thermally excited singlet and the other from the lowest triplet state ( ). The quantum yield is temperature dependent, the activation energy for the decomposition of the triplet being estimated at 16 kcal mol". There is evidence that the excited singlet hexafluoroacetone can undergo cyclic addition with perfluoroolefins to form the corresponding oxetane (4). This reaction involves addition of the triplet state of the ketone to the electron deficient double bond of the fluoroolefin( ). 

Kinetic measurements of the ring-opening polymerization of trimethylene carbonate (TMC) versus the enchainment of oxetane and CO2 to provide poly (TMC) reveal that these processes in the presence of (salen)CrCl and an ammonium salt have similar free energies of activation (AG ) at 110°C. This similarity in reactivity coupled with the observation that in situ infrared studies of the copolymerization of oxetane and CO2 showed the presence of TMC during the early stages of the reaction has led to the overall mechanism for copolymer production shown in... 

The mechanism of decarboxylation of /3-lactones has attracted much attention. The gas-phase decomposition of 2-oxetanone is a unimolecular first-order process. It has a considerably lower energy of activation than the pyrolysis of oxetane and a much higher entropy of activation, indicating a loose activated complex (69JA7743). The ease of the reaction is greatly affected by the electronic effect of substituents at position-4, but not at position-3. The Hammett treatment of a series of rrans-4-aryl-3-methyl-2-oxetanones gave a good correlation with [Pg.374]

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