Empirical quantitative correlation of substituent size with proton nuclear magnetic resonance chemical shift difference between nonequivalent geminal methylene protons of hindered N-substituted acetanilides and difluorooxyboranes

Benjamin Staskun*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    7 Citations (Scopus)

    Abstract

    In N-ethyl- and N-benzyl-substituted difluorooxyboranes nonequivalence of the geminal methylene protons is exhibited in the 1H NMR (CDCl3) when the neighboring ortho X substituent on the arylamido moiety is sufficiently large. The observed chemical shift difference (ΔδAB) correlates quantitatively with the van der Waals radius (or a specially assigned "effective radius", rX) of the X substituent, and the linear relationship (ΔδAB = arX + b) is rationalized in terms of a preferred conformation for the difluorooxyborane. The correlation also extends to the hindered N-substituted acetanilides.

    Original languageEnglish
    Pages (from-to)1643-1646
    Number of pages4
    JournalJournal of Organic Chemistry
    Volume46
    Issue number8
    Publication statusPublished - 1981

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