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.
|Number of pages||4|
|Journal||Journal of Organic Chemistry|
|Publication status||Published - 1981|