A series of O-(diethyl phosphoryl) and O-(methylcarbamoyl) oximes of substituted acetophenones and α-substituted benzaldehydes were evaluated for anticholinesterase activity, toxicity to insects, and for chemical reactivity. Multiple regression analysis was used to correlate reactivity and biological data with free energy parameters. Excellent correlation was obtained between electronic effects, reactivity and anticholinesterase activity for the ring-substituted acetophenone O-(diethyl phosphoryl)oximes and O-(methylcarbamoyl)oximes. With the α-substituted benzaldehyde O-(methylcarbamoyl)oximes, the addition of Hansch's π constant to the regression equation was necessary to provide correlation with anticholinesterase activity. An unusual example of the Beckmann rearrangement was discovered and the high reactivity of substituted acetophenone O-(diethyl phosphoryl)oximes containing electrondonating substituents is explained in terms of this rearrangement. © 1969, American Chemical Society. All rights reserved.