Activation energy vinyl allyl ether

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. 

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... 

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 ...

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. 

C-0 bond in alkyl aryl ethers is more resistant toward cleavage than that in allyl or vinyl ethers. In alkyl aryl ethers such as anisole, activation of RO-Ar bond (type a in Scheme 3.41) is difficult in comparison with that of R-OAr bond (type b), probably because the relatively stronger bond dissociation energy of the aryl-0 bond than that of alkyl-0 bond due to aromatic conjugation as well as higher stability of aryloxo-metal products. 

In a more recent study, Hillier placed two water molecules around the oxygen of allyl vinyl ether and its transition state for formation of 4-pentenal in an MP2/RHF/6-31G calculation [56]. When the SCRF model was used, no net decrease in activation free energy was obtained at the /= 1 level (atomic monopoles) and lack of convergence accompanied attempts to use higher terms in the multipole expansion. However, the PCM model provided a net energy decrease of 4.3kcalmol, which corresponds favorably to experiment. Somewhat disconcerting, however, were the calculated kinetic isotope effects = 1.149 and =0.919), which differed from the exper-... 

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