52 samples of 4,4'-disubstituted N-benzylidenebenzenamine (p-XPhCH=NC 6 H 4 Y-p) derivatives were synthesized, the effect of substituents on the reduction potential E Red of these compounds was systematically investigated. The result shows that there is not linear relation between their E Red and the chemical shift δ C (C=N) of the 13 C NMR of C=N bridge bond in the molecules. The factors affecting E Red are obvious different from that affecting on δ C (C=N), and the change regularity of E Red can not be expressed well by only employing Hammett substituent constant. The main factors affecting the E Red are the field/inductive effect of substituent X, the conjugative effects of substituents X and Y, and the excited-state substituent constant of substituent X plays an important role of influence on E Red. Above four parameters have good correlations with the E Red of the 52 samples of compounds, the correlation coefficient of the correlation equation is 0.9756, and the standard derivation is 0.052 V. Among the four factors, the contributions of the field/inductive effect, the conjugative effect and the excited-state substituent constant of group X to the changes of E Red are relative large, while the contribution of the conjugative effect of group Y is relative small, and can not be ignored.
Thirty-six samples of disubstituted N-phenyl-α -phenylnitrones, XArCH = N(O)ArY (XPNY), were synthesized. The effects of their substituents on their reduction potentials (Ered) were investigated by systematically comparing the Ered differences for XPNY versus XArCH = NArY (XBAY) and XPNY versus XArC(Me)=NArY (XPEAY). The results show the following: there is no linear relationship between the Ered values and 13 C NMR chemical shifts, δC(C=N), of the C=N bridging bond for XPNY; there are no linear relationships among the Ered values for XPNY versus XBAY and XPNY versus XPEAY, i.e., their Ered values show their own specific regular changes; the excited-state substituent effect of X and the indicating parameter of the metaposition group make important contributions to the Ered values of XPEAY and XBAY, but have little effect on Ered of XPNY; the excited-state substituent effect of the Y group contributes to the XPNY Ered, but rarely contributes to the Ered values of XPEAY and XBAY, and can be ignored; the parents of XBAY and XPNY have similar reduction potentials, but the reduction potential of the parent of XPEAY is lower than those of XBAY and XPNY. In general, XPEAY is more difficult to be reduced than XBAY or XPNY, for these three types of compound with X-Y group couples.
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