Thermodynamic Rearrangement

Lassila, K. R., Ford, M. E. Solid acid catalysis of the Fries rearrangement thermodynamic limitations based on solvent polarity. Chem. Ind. 1992,47, 169-180. 

The rearrangement of carbonium ions that readily occurs according to the thermodynamic stabiUty of cations sometimes limits synthetic utility of aromatic alkylation. For instance, the alkylation of ben2ene with / -propyl bromide gives mostly isopropylben2ene (cumene) much less... 

Trifluoromethylpteridine and its 7-methyl and 6,7-dimethyl derivatives (69JCS(C)l75l) are, as expected, even more subject to hydration. The first two are essentially completely hydrated across the 3,4-double bond at equilibrium in neutral solution and the last is partly hydrated. On dissolution of 4-trifluoromethylpteridine in aqueous acid the 5,6,7,8-dihy-drated cation is the main product initially, rearranging more slowly to the thermodynamically more stable 3,4-hydrate. 

The ring contraction of a cyclohexyl cation to a methylcyclopentyl cation is thermodynamically favorable but would require a substantial energy of activation if the rearrangement proceeded through a primary cyclopentylmethyl catiotL... 

The most important sigmatropic rearrangements from the synthetic point of view are the [3,3] processes involving carbon-carbon bonds. The thermal rearrangement of 1,5-dienes by [3,3] sigmatropy is called the Cope rearrangement. The reaction establishes equilibrium between the two 1,5-dienes and proceeds in the thermodynamically favored direction. The conversion of 24 to 25 provides an example ... 

Reaction of A with water under kinetic control conditions leads to the 5)5,19-cyclo-6 -ol (69a), whereas under conditions of thermodynamic control A rearranges to the isomeric cation B which reacts with water to give the B-homo-7)5-ol (70a). 

The yields of thermal rearrangements of some perfluorinated olefins are very low The fact that perfluorocyclobutene yields perfluoro-l,3-butadiene at 650 °C only in a 12% yield [7] is due to the higher thermodynamic stability of perfluoro cyclobutene compared with the-open chain product [72 ]... 

Rearrangement studies give an interesting insight into the specific effect of fluonne on the thermodynamic stability and rearrangement kinetics of fluonnated cyclopropanes Fluorine decreases the thermodynamic stability of the cyclopropyl nng, in contrast with the generally observed effect of fluonne increasing the stability of molecules to which it is introduced [124]... 

Would you describe the transition state for the Claisen rearrangement as early (like reactants), late (like products) or in between Given the overall thermodynamics of reaction, do you conclude that the Hammond Postulate applies Explain. 

Assignment of the l,2,4-triazolo[l,5-c]pyrimidine structures to the products obtained from the previously described cyclizations and not the alternative [4,3-c] structures has been rationalized and corroborated on the basis of (a) preference of cyclization at the more nucleophilic triazole ring N2 rather than at its less nucleophilic N4 (65JOC3601 88JMC1014), (b) inability of the obtained products to undergo acid- or base-catalyzed Dimroth rearrangement, a property characteristic of the thermodynamically less stable [4,3-c] isomers (91JMC281), (c) comparison with unequivocally prepared... 

Tlie thermodynamically more stable l,2,4-triazolo[l,5-c]pyrimidines 23 were frequently prepared by Dimroth rearrangement of their thermody-... 

This reaction proceeds by a concerted, [3,3] sigmatropic rearrangement (cf. the Claisen rearrangement) where one carbon-carbon single bond breaks, while the new one is formed. It is a reversible reaction the thermodynamically more stable isomer is formed preferentially ... 

The vapor-phase chlorination reaction occurs at approximately 200-300°C. The dichlorobutene mixture is then treated with NaCN or HCN in presence of copper cyanide. The product 1,4-dicyano-2-butene is obtained in high yield because allylic rearrangement to the more thermodynamically stable isomer occurs during the cyanation reaction ... 

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