Linked Life Data

19711937

Source:http://linkedlifedata.com/resource/pubmed/id/19711937

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PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
38
pubmed:dateCreated
2009-9-17
pubmed:abstractText
Enthalpies for bond-forming reactions that are subject to organocatalysis have been predicted using the high-accuracy CBS-QB3 model chemistry and six DFT functionals. Reaction enthalpies were decomposed into contributions from changes in bonding and other intramolecular effects via the hierarchy of homodesmotic reactions. The order of the reaction exothermicities (aldol < Mannich approximately alpha-aminoxylation) arises primarily from changes in formal bond types mediated by contributions from secondary intramolecular interactions. In each of these reaction types, methyl substitution at the beta- and gamma-positions stabilizes the products relative to the unsubstituted case. The performance of six DFT functionals (B3LYP, B3PW91, B1B95, MPW1PW91, PBE1PBE, and M06-2X), MP2, and SCS-MP2 has been assessed for the prediction of these reaction enthalpies. Even though the PBE1PBE and M06-2X functionals perform well for the aldol and Mannich reactions, errors roughly double when these functionals are applied to the alpha-aminoxylation reactions. B3PW91 and B1B95, which offer modest accuracy for the aldol and Mannich reactions, yield reliable predictions for the two alpha-aminoxylation reactions. The excellent performance of the M06-2X and PBE1PBE functionals for aldol and Mannich reactions stems from the cancellation of sizable errors arising from inadequate descriptions of the underlying bond transformations and intramolecular interactions. SCS-MP2/cc-pVTZ performs most consistently across these three classes of reactions, although the reaction exothermicities are systematically underestimated by 1-3 kcal mol(-1). Conventional MP2, when paired with the cc-pVTZ basis set, performs somewhat better than SCS-MP2 for some of these reactions, particularly the alpha-aminoxylations. Finally, the merits of benchmarking DFT functionals for the set of simple chemically meaningful transformations underlying all bond-forming reactions are discussed.
pubmed:grant
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Sep
pubmed:issn
1520-5215
pubmed:author
pubmed:issnType
Electronic
pubmed:day
24
pubmed:volume
113
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
10376-84
pubmed:dateRevised
2010-9-27
pubmed:meshHeading
pubmed:year
2009
pubmed:articleTitle
Accurate reaction enthalpies and sources of error in DFT thermochemistry for aldol, Mannich, and alpha-aminoxylation reactions.
pubmed:affiliation
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, Non-P.H.S., Research Support, Non-U.S. Gov't, Research Support, N.I.H., Extramural