The vibrational spectra of 2-amino-5-chlorobenzonitrile was studied using density functinal theory. 2-Amino-5-chlorobenzonitrile was used to build up the 2,2-dioxide-1H-2,1,3-benzothiadiazine ring system. The vibrational spectra of 2-amino-5-chlorobenzonitrile was studied using density functinal theory. 2-Amino-5-chlorobenzonitrile was used to build up the 2,2-dioxide-1H-2,1,3-benzothiadiazine ring system.