You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Synthesis and anti-acetylcholinesterase properties of novel β- and γ-substituted alkoxy organophosphonates. Activated organophosphate (OP) insecticides and chemical agents inhibit acetylcholinesterase (AChE) to form OP-AChE adducts. Whereas the structure of the OP correlates with the rate of inhibition, the structure of the OP-AChE adduct influences the rate at which post-inhibitory reactivation or aging phenomena occurs. In this report, we prepared a panel of β-substituted ethoxy and γ-substituted propoxy phosphonoesters of the type p-NO(2)PhO-P(X)(R)[(O(CH(2))(n)Z] (R=Me, Et; X=O, S; n=2, 3; Z=halogen, OTs) and examined the inhibition of three AChEs by select structures in the panel. The β-fluoroethoxy methylphosphonate analog (R=Me, Z=F, n=2) was the most potent anti-AChE compound comparable (ki ∼6 × 10(6)M(-1)min(-1)) to paraoxon against EEAChE. Analogs with Z=Br, I, or OTs were weak inhibitors of the AChEs, and methyl phosphonates (R=Me) were more potent than the corresponding ethyl phosphonates (R=Et). As expected, analogs with a thionate linkage (PS) were poor inhibitors of the AChEs.
{"Chemical": ["Et", "thionate", "I", "R=Me, Et; X=O, S; n=2, 3; Z=halogen, OTs", "F", "R=Me, Z=F, n=2", "Z=Br, I, or OTs", "Me", "R=Me", "organophosphate", "\u03b2-fluoroethoxy methylphosphonate", "OTs", "\u03b2- and \u03b3-substituted alkoxy organophosphonates", "methyl phosphonates", "R=Et", "Br", "ethyl phosphonates", "\u03b2-substituted ethoxy and \u03b3-substituted propoxy phosphonoesters", "O", "S", "p-NO(2)PhO-P(X)(R)[(O(CH(2))(n)Z]", "paraoxon", "halogen"]}