Theoretical estimates of the height of the barrier to inversion have been made by Shoppee (1946), 9-10 kcal mole-1, and Beckett et al. (1947), 14 kcal mole-1. A more recent theoretical estimate is that by Hendrickson (1961), 12-7 kcal mole-1. The symmetry of the intermediate boat form assumed in these calculations suggests an entropy of activation of 4-9 e.u. The diagram of Jensen et al. (1962), given as Fig. 21, is undoubtedly quite [Pg.235]

Adapted from Cortright et al. (55). Difference between theoretical A G° (see Table V) and the fitted A G° of this table. Fitted parameter is the rato of surface entropy to the DFT-predicted entropy for the adsorbed species. The value of this parameter was found to be 1.4 0.15. Parameters maintained at values predicted by DFT calculations (see Table V). Value constrained such that adsorbed hydrogen does not exceed two degrees of translational mobility. - Fitted parameter is the ratio of surface entropy of the activated complex to the DFT-predicted entropy of that activated complex. The value of this parameter was found to be 0.86 0.13. Value constrained to be within 50 kJ/mol of the theoretical value. [Pg.216]

K. N. Houk, N. G. Rondan, and J. Mareda, Theoretical Studies of Halocarbene Cycloaddition Selectivities. A New Interpretation of Negative Activation Energies and Entropy Control of Selectivities, Tetrahedron 1985, 41, 1555. Calculations on carbene addition reactions led to a general explanation of why it is possible for very exothermic, bimolecular reactions to have negative activation enthalpies. [Pg.1000]

Hcuts et a .,64 while not disputing that penultimate units might influence the activation energies, proposed on the basis of theoretical calculations that penultimate unit effects of the magnitude seen in Ihe S-AN and other systems (i.e. 2-5 fold) can also be explained by variations in the entropy of activation for the process. They also proposed that this effect would mainly influence rate rather than specificity. [Pg.350]

© 2019 chempedia.info