Synonyms: 2,2,5,5-Tetramethyl-3-carboxypyrrolidine-N-oxyl;2,2,5,5-Tetramethyl-3-carboxypyrrolidinooxy; 2,2,5,5-Tetramethylpiperidine-1-oxyl-3-carboxylicacid; 2,2,5,5-Tetramethylpyrrolidine-1-oxyl-3-carboxylic acid;3-Carboxy-1-oxyl-2,2,5,5-tetramethylpyrrolidine;3-Carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy;3-Carboxy-2,2,5,5-tetramethylpyrrolidin-1-oxy; 3-Carboxy-2,2,5,5-tetramethylpyrrolidine-1-oxyl;3-Carboxy-2,2,5,5-tetramethylpyrrolidinyloxy;3-Carboxy-2,2,5,5-tetramethylpyrrolidinyloxyl;DL-3-Carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxyl; NSC 158842; PCA; PCA(radical); T 517