Activation energy allyl ether

Ab initio molecular orbital calculations, coupled with activation energies and entropies from experimental data, have been employed to determine the nature of the intermediates in the reaction of singlet oxygen with alkenes, enol ethers, and enamines.214 Allylic alkenes probably react via a perepoxide-like conformation, whereas the more likely pathway for enamines involves a zwitterionic cycloaddition mechanism. The reactions of enol ethers are more complex, since the relative stabilities of the possible intermediates (biradical, perepoxide, and zwitterionic) here depend sensitively on the substituents and solvent polarity. 

The effects of solvation have been studied by an implementation of an ellipsoid cavity model into Kohn-Sham theory [94]. The lowering of the activation energy by water solvation of the allyl vinyl ether has been calculated to be 0.3 kcal/mol by this method. This value is considerably lower than the results from other calculations on the same system using cavity models [95], free energy perturbation [96], or QM/MM calculations [97] as well as the values... 

Gas phase kinetic data have been reported for only two of these reaction subclasses, allyl esters (2), and vinyl allyl ethers (4). Subclasses (5), (6) and (1) have very fast reverse processes (see activation energy predictions), but could be observed in terms of loss of optical activity at the 4-position. It would be interesting to look for these reactions. 

Similar activation parameters have been observed for Cope rearrangements in diene systems that incorporate a heteroatom. For the rearrangement of allyl vinyl ether to 4-pentenal, the activation energy is 30.6 kcal/mol and the entropy of activation is -8 eu ... 

The bond lengths in the optimized transition structures at the three levels of theory are tabulated (Table 4.1). B3LYP/6-31G gave the best agreement with activation energy relative to the experimentally observed activation every of the rearrangement of 2-OTMS allyl vinyl ether. The calculated relative activation energies for the 2-OH versus the parent allyl vinyl ether were most accurate at the RHF/ 6-31G level. 

Scheme 11.41 Predicted structural and energetic data for the Claisen rearrangement of 2-substitued allyl vinyl ethers according to Aviyente and Houk (2001) [57], Gas-phase calculations were performed on the B3LYP/5-31G level of theory./< = dipole moment, AS = charge separation in the transition state, A = reaction energy, AE" = activation energy, = relative intrinsic contribution to the activation energy ...

In addition to ethylene and propylene oxide, a variety of other cyclic ethers have also been copolymerized with MA. Monomers such as cyclohexene oxide,piperylene dimer mono and diepoxide, epichlorohydrin, " " 3,3,3-trichloropropylene oxide, " tetrahydrofuran, " " and ethylene carbonate or ethylene sulfite " have received attention. Condensation reactions between allyl glycidyl ether and MA are reported to be highly useful for preparing plastics with remarkable hardness, high heat distortion, and brilliant clarity.The cyclohexene oxide copolymerizations were second order in MA, with an activation energy of 13.8 kcal/mol. For the epichlorohydrin system the rate was dependent on the temperature and proportional to the catalyst concentration, with an activation energy of 14.5 kcal/mol. 

The discovery of coordinate polymerization of oxirane led to an enormous expansion in the range of polyether structures that could be synthesized. Some of the remarkable synthesis chemistry is outlined in Section III. Coordinate copolymerization further increased the range of polymer structures that could be synthesized in highly controlled ways. Two examples have already been described copolymers of epichlorohydrin and ethylene oxide (71) and of propylene oxide and allyl glycidyl ether (94, 137). The activation energy for copolymerization of epichlorohydrin and maleic anhydride was found to be 14.5 kcal/mol, and the polymerization rate is dependent on temperature and proportional to catalyst concentration (138-140). 

Table 11 Transition-structure Geometries and Activation Energies of the [3,3]-Sigmatropic Shift of Allyl Vinyl Ether...

A comparison between experimental and MO data on regioselectivity concerning the hydroformylation of several vinyl substrates (propene, 2-methylpropene, 1-hexene, 3,3-dimethylbutene, fluoroethene, 3,3,3-trifluoropropene, vinyl methyl ether, allyl methyl ether, styrene) with unmodified rhodium catalysts was reported. The activation energies for the alkyl rhodium intermediate formation, computed at either level along the pathways to branched or linear aldehydes, allowed one to predict the regioselectivity ratios. Steric effects may be less important for the unmodified carbonyl complexes and electronic factors dominate, assuming that alkene insertion in Rh-H is irreversible. 

KF is ineffective in the reaction, even when activated by a crown ether. This allylation apparently involves cleavage to a and b, which adds to the carbonyl group to give c, and is possible because of the high Si—F bond energy. Aldehydes are more reactive than ketones. 

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