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Imidacloprid and a series of the related compounds were synthesized, and influence of 3-N substituents(R) on the insecticidal activities against Brown plant hopper(Nilaparvata lugens) and Green peach aphid(Myzus persicae) were examined quantitatively from the structure-activities relationships(SAR) techniques. The results indicated that the molecular hydrophobicity(π) and inductive substituent constant(σ^*) of substituents(R) at 3-nitrogen position on the imidazolidine ring were important factors. Variations in the potency were parabolically related to the both constants. In case of Brown plant hopper, optimum value of π constant was 0.52, whereas the value of σ^* constant against Green peach aphid was 1.17, respectively. Among them, the strong electron withdrawing groups(σ^*$gt;0) such as methyl and benzenesulfonyl group(7 & 8) showed lower insecticidal activity and non-substituted, 1(imidacloprid) showed the best insecticidal activity. It seems that the intramolecular associated(H-bond) form between 2-N-nitro group and 3-imid group may contribute to the higher insecticidal activity to the both sucking insects. And in aqueous solution, 1 showed higher residual activity below pH 6.0, and the half-life(T_½) was about 6 month at pH 7.0 (ca. k_(obs) : 5×10^(-8) sec.^(-1)) and 45℃.
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