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** Conformation energy calculations **

Theoretical calculations (6-31G ) have been used to compare the energies of four possible transition states for Diels-Alder reaction of the BF3 complex of methyl acrylate with 1,3-butadiene. The results are summarized in Fig. 6.4. The endo transition state with the s-trans conformation of the dienophile is preferred to the others by about 2kcal/mol.14 [Pg.337]

The selection of theoretical model with which to obtain the energy profile should be based on documented performance with regard to calculation of relative conformer energies and barrier heights. Full discussion has already been provided in Chapter 8. [Pg.407]

The situation appears decisively different in 3-formyl derivatives. Theoretical calculations (77JCS(P2)1601 79NJC473) reveal a small energy difference between X,0-cis and X,0-trans conformations in furan-3-carboxaldehyde (4, X = O), and pyrrole-3-carboxaldehyde (4, X = NH), and the X,0-cis form is [Pg.94]

In mobile equilibria, the increase in the dielectric constant of the solution should enhance the population of the conformer with higher polarity (SOM 18), as is also proved by theoretical calculations. The solvation energy may lead to inversion in isomer stability on going from the vapor phase to a solution of a certain polarity, as occurs for furan-2-carboxaldehyde (72T3015). Inversion in conformer stability may also occur on going from the vapor to the liquid or solid state. [Pg.166]

** Conformation energy calculations **

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