The Substituent Effect. VII. Substituent Chemical Shifts of NH Proton of Acetanilides

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概要

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• NMR chemical shifts of the NH proton of fifty-three <I>m</I>- and <I>p</I>-substituted acetanilides were determined in dilute DMSO solutions. The substituent chemical shifts were correlated with σ<SUP>0</SUP> constants with considerable scatter. Deviations Were particularly significant for −<I>R</I> groups having α-hydrogen. Improved correlation was found for −<I>R</I> substituents with (σ<SUP>0</SUP>)<SUB>DMSO</SUB> values which had been derived from the phenol hydroxyl chemical shifts in DMSO. Application of the LArSR equation using the DMSO-modified substituent parameters gave a good linear correlation for all substituents; <I>Δ</I>δ<SUP>NHAc</SUP>=0.686 [(σ<SUP>0</SUP>)<SUB>DMSO</SUB>+0.277 (<I>Δ</I>\barσ<SUB>R</SUB><SUP>−</SUP>)<SUB>DMSO</SUB>]. These results indicate that the deviations are caused primarily by solvent-modification of substituents, the modification being essentially the same for both the acetanilide and the phenol systems in DMSO. The lower <I>r</I><SUP>−</SUP> value 0.277 in the chemical shifts for the acetanilides than for the phenols suggests that the π-electronic contribution of +<I>R</I> <I>para</I> substituents is less important in the acetanilide system than in the phenol one. The resonance substituent parameter for these solvent-modified substituents was found to be proportional to both (\barσ<I><SUB>p</SUB></I><SUP>OH</SUP>−\barσ<I><SUB>p</SUB></I><SUP>NH</SUP>), the difference between the apparent \barσ<I><SUB>p</SUB></I> constants of the two systems, and to \barσ<I><SUB>p</SUB></I>−0.85\barσ<I><SUB>m</SUB></I> of each series. Estimation of a practical set of inductive and resonance substituent parameters for DMSO-modified substituents is attempted.

• 公益社団法人 日本化学会の論文

著者

• TAKAI Yoshio

  Institute of Scientific and Industrial Research, Osaka University

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• The Substituent Effect. VII. Substituent Chemical Shifts of NH Proton of Acetanilides

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