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:

Isolation of a p-hydroxyphenyl anhydride from the leaves of Diphysa carthagenensisw. Diphysidione (1), a new p-hydroxyphenyl anhydride, and vitexin (2) were isolated from the leaves of Diphysa carthagenensis. The structure of the new metabolite was characterised as 4-(4-hydroxy-phenyl)-3H-pyran-2,6-dione using 1D and 2D NMR spectroscopy.
{"Chemical": ["4-(4-hydroxy-phenyl)-3H-pyran-2,6-dione", "p-hydroxyphenyl anhydride", "vitexin", "Diphysidione"]}