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Identification and characterization of biproducts/ impurities present in agrochemicals are critical in view of their efficacy and safety towards public health. We herein present our study on identification and characterization of an impurity, 5‐chloro‐2‐cyano‐N,N‐dimethyl‐4‐p‐tolylimidazole‐1‐sulfonamide (2) present in the fungicide, "cyazofamid". Intermittent HPLC analysis of the reaction of substituted imidazole (1) with N,N‐dimethylsulfamoyl chloride suggested that 2 is formed during the reaction. Isolation by preparative HPLC and characterization by NMR, LC/HRMS, MS/MS and single crystal XRD analysis confirmed 2 as an isomer of cyazofamid, wherein the N,N‐dimethyl sulfonamide group was positioned on the other nitrogen of imidazole in close proximity to chloride group. Computational studies further supported the formation of 2 and ruled out the other possible isomeric structures. [ABSTRACT FROM AUTHOR]