Abstract:

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 (E_red) were investigated by systematically comparing the E_red 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 E_red values and ¹³C NMR chemical shifts, δ_C(C＝N), of the C＝N bridging bond for XPNY; there are no linear relationships among the E_red values for XPNY versus XBAY and XPNY versus XPEAY, i.e., their E_red 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 E_red values of XPEAY and XBAY, but have little effect on E_red of XPNY; the excited-state substituent effect of the Y group contributes to the XPNY E_red, but rarely contributes to the E_red 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.

Key words: N-Phenyl-α-phenylnitrone, Substituent effect, Chemical shift, Reduction potential, Excited-state substituent parameter, Indicating parameter