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:

Chemical variability of Algerian Myrtus communis L. The composition of 55 samples of essential oil isolated from the aerial parts of wild growing Myrtus communis L. harvested in 16 locations from East to West Algeria were investigated by GC (determination of retention indices) and (13) C-NMR analyses. The essential oils consisted mainly of monoterpenes, α-pinene (27.4-59.2%) and 1,8-cineole (6.1-34.3%) being the major components. They were also characterized by the absence of myrtenyl acetate. The compositions of the 55 oils were submitted to k-means partitioning and principal component analysis, which allowed the distinction of two groups within the oil samples, which could be subdivided into two subgroups each. Groups I (78% of the samples) and II were differentiated on the basis of the contents of α-pinene, linalool, and linalyl acetate. Subgroups IA and IB could be distinguished by their contents of α-pinene and 1,8-cineole. Subgroups IIA and IIB differed substantially in their contents of 1,8-cineole and limonene. All the samples contained 3,3,5,5,8,8-hexamethyl-7-oxabicyclo[4.3.0]non-1(6)-ene-2,4-dione (up to 4.9%).
{"Chemical": ["3,3,5,5,8,8-hexamethyl-7-oxabicyclo[4.3.0]non-1(6)-ene-2,4-dione", "myrtenyl acetate", "\u03b1-pinene", "linalool", "1,8-cineole", "monoterpenes", "linalyl acetate", "(13) C", "limonene"]}