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Study of prototypical Diels-Alder reactions by a hybrid density functional/Hartree-Fock approach

✍ Scribed by Vincenzo Barone; Roger Arnaud

Publisher: Elsevier Science
Year: 1996
Tongue: English
Weight: 537 KB
Volume: 251
Category: Article
ISSN: 0009-2614
DOI: 10.1016/0009-2614(96)00072-3

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✦ Synopsis

Kinetic and thermodynamic parameters for the Diels-Alder reactions of butadiene with ethylene, formaldehyde and thioformaldehyde have been computed by a density functional method (B3LYP) which incorporates gradient corrections and some Hartree-Fock exchange. Post Hartree-Fock computations have also been performed for comparison. The activation energies computed for the addition of C2H 4 at the B3LYP and QCISD[T] levels approach the experimental value, whereas HF and MP2 approaches are not sufficiently reliable. The computed activation energy for H2CO is close to that for C2H 4 by the B3LYP approach, whereas it significantly decreases at MP2. QCISD[T] computations give an intermediate result. A low activation energy is computed for H2CS, in agreement with observations that thioaldehydes and activated thioketones rapidly undergo hetero-Diels-Alder reactions at or below room temperature. The B3LYP result is closer to the QCISD[T] reference than the MP2 value. These trends have been interpreted by interactions between frontier orbitals or by energy partitioning based on natural bond orbitals.

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