Lipophilicity and the tendency for decomposition of imidac}oprid and related compounds by oxygen, hydrolytic mediums, and simulated sunlight were studied to see whether these physicochemical faetors haye any relation to the biological actiyity of the compounds in vitro, in a greenhouse, or under field conditions. Lipophi]icity indices based on HPLC bore no definite relationship with the binding aMnity to the acetylcholine receptor. Howeyer, the compounds haying high insecticidal potential in greenhouse tests were generally less hydrophilic. In neutral water or in an oxygen-saturated solution, the compounds tested were completely stable.Aneyidentdifferencewasobseryedintheirbehayiortowardthesunlightwayelength,thenitromethylene compounds decomposing far more rapidly than nitroimines like imidacloprid. The photolability of the nitromethylenes is ascribed to their longer maximum absorption wayelength of oyer 320nm. Imidacloprid(21),1-(6-chloronicotinyl)-2-nitroiminoimidespecially connected with the in vivo behavior of the azolidine, is a new insecticide with high activity especially molecules. However, we have not dealt here with the against sucking pests.2) The cliscovery of this compound behavior in soil, another important degradation pathway was the result of seeking improved activity by changing the for pesticides. structure of the originally announced insecticide, 2nitromethylenetetrahydrothiazine (SKI-71; 33).3) We have Materials and Methods prepared about 2000 compounds and selected imidacloprid Matexiais. The reagents and solvents used were of ttnalyticul grade. The for commercial use based on, above all, its insecticidal following compounds were prepared aocording to the descriptions in the gg`.