Comparison of gas-phase acidities of some carbon acids with their rates of hydron exchange in methanolic methoxide

Vincent F. DeTuri, Heinz F. Koch, Judith G. Koch, Gerrit Lodder, Masaaki Mishima, Han Zuilhof, Neal M. Abrams, Cecily E. Anders, Justin C. Biffinger, Patrick Han, Adam R. Kurland, Jason M. Nichols, Anne M. Ruminski, Patricia R. Smith, Karen D. Vasey

    Research output: Contribution to journalArticlepeer-review

    8 Citations (Scopus)

    Abstract

    Hydron exchange reaction rates, kexch M-1s -1, using methanolic sodium methoxide are compared with gas-phase acidities, ΔGAcid0 kcal/mol, for four 9-YPhenylfluorenes-9-iH, seven YC6H4C iH(CF3)2, seven YC6H 4-CiHClCF3, and C6F5 iH. Fourteen of the fluorinated benzylic compounds and pentafluorobenzene result in near unity experimental hydrogen isotope effects that suggest substantial amounts of internal return associated with the exchange process. Although the reactions of 9-phenylfluorene have experimental isotope effects that appear to be normal in value, they do not obey the Swain-Schaad relationship. This suggests that they occur with small amounts of internal return. The entropies of activation, ΔS‡, are +12 to +14 eu, for the benzylic compounds and different significantly from those for the 9-YPhenylfluorenes, ΔS‡ of -8 to -12 eu. The ΔS‡ ∼ 1 eu for the reactions of pentafluorobenzene falls between the other compounds. Density functional calculations using B3LYP/6-31+G(d,p) are reported for the reactions of CH3O-(HOCH3)3 with C6F5H, C6H5CH(CF3) 2, C6H5CHlCF3, and 9-phenylfluorene.

    Original languageEnglish
    Pages (from-to)308-317
    Number of pages10
    JournalJournal of Physical Organic Chemistry
    Volume19
    Issue number5
    DOIs
    Publication statusPublished - 2006 May

    Keywords

    • B3LYP/6-31+G(d,p) calculations
    • Kinetic acidities
    • Methanolic sodium methoxide
    • ΔG (gas phase)

    ASJC Scopus subject areas

    • Physical and Theoretical Chemistry
    • Organic Chemistry

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