Understanding alkyl substituent effects in R–O bond dissociation reactions in open- and closed-shell systems

Michelle Coote, Addy Pross, Leo Radom

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review


The effects of alkyl substituents (R = Me, Et, i-Pr and t-Bu) on the barriers and enthalpies for R–O bond dissociation reactions are examined via high-level ab initio molecular orbital calculations for the open-shell systems, R–OCH2• and R–OC(SCH3)2•. To assist in the interpretation of the results, R–X bond dissociation energies (BDEs) are also examined in the closed-shell systems (X = H, CH3, OCH3, OH and F). The effects of increasing alkylation on the R–O bond dissociation reactions show an unusual and somewhat counterintuitive trend. Specifically, the BDEs broadly increase and the barriers decrease in going from R = Me to R = t-Bu. However, on closer examination, these effects are readily understood in terms of the competing effects of hyperconjugative stabilization of the leaving R• radical and charge-transfer stabilization of the R–O bond. As part of this work, we also show that B3-LYP yields the wrong qualitative trends for the effect of alkyl substituents on the R–O BDEs.
Original languageEnglish
Title of host publicationFundamental World of Quantum Chemistry
Subtitle of host publicationA Tribute to the memory of Per-Olov Löwdin
EditorsErkki J. Brandas, Eugene S. Kryachko
Place of PublicationDordrecht
ISBN (Electronic)9789401704489
ISBN (Print)9789048166879
Publication statusPublished - 2004
Externally publishedYes


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