However, in the present work we carried out calculations that show

However, in the present work we carried out calculations that show

Poster B.10
AB INITIO AND DFT STUDY OF THE DIELS-ALDER REACTION BETWEEN
1,2,4-PENTATRIENE AND ETHYLENE.
Mª Luisa Ferreiro and Jesús Rodríguez-Otero.
Depto. Química Física, Fac. Química, Universidad de Santiago de Compostela
Santiago de Compostela, Galicia (Spain).
Recently, M. Manoharan and P. Venuvanalingam [J. Chem. Soc., Perkin Trans. 2, (1997)
1799-1804] have shown that replacement of butadiene for 1,2,4-pentatriene (or vinylallene)
have a negative effect over the reaction rate of the simplest Diels-Alder cycloaddition. So, these
authors calculate a slightly higher activation energy.
+
However, in the present work we carried out calculations that show the opposite effect:
a significant decrease of the activation energy. The reason for this discrepancy could be
the insufficient level of the previous calculations. According to our results, the
activation energy for the butadiene-ethylene reaction is 24.91, 25.28 and 26.46 kcal/mol
from the MP4SDTQ/6-31G*//MP2/6-31G*, MP4SDTQ/6-31+G*//MP2/6-31G* and
B3LYP/6-31G** levels, respectively. These values are in very good agreement with the
experimental findings (25.1 kcal/mol). At the same levels of calculation, the substitution
of diene for vinylallene give rise to the next values: 21.61, 21.18 and 23.81 kcal/mol,
respectively. Complementary natural bond orbital (NBO) computations have been used
to assess the observed decreases.
149.0º
(150.0º)
2.244
(2.277)
2.356
(2.384)
B3LYP/6-31G**
(MP2/6-31G*)