eng Science and Education Publishing World Journal of Chemical Education 2375-1657 2022-06-23 10 3 91 94 10.12691/wjce-10-3-1 WJCE20221031 article R. Sanjeev 1 V. Jagannadham jagannadham1950@yahoo.com 2 Department of Chemistry, Geethanjali College of Engineering and Technology, Cheeryal-501301, Telangana, India Department of Chemistry, Osmania University, Hyderabad-500007, India Hammett values are estimated for the two acid dissociation equilibriums eqn. 1 and 2 of pyridinium and pyridazenium ions from the Hammett plots of log KaH versus Hammett values. The Hammett values are found to be 5.94 and 5.29 for the two equilibriums eqns. 1 and 2 respectively. The effect of extra pyridine type nitrogen (=N-) on Hammett is discussed. Similarly, the average lone pair ionization potentials (IP) of pyridines and pyridazines also followed Hammett equation with Hammett of 1.18 for pyridines and 0.38 for pyridazines respectively. This article is useful in an undergraduate and graduate classroom who tries to study the substituent effects and reactivity-selectivity principle. http://pubs.sciepub.com/wjce/10/3/1/wjce-10-3-1.pdf pyridiene pyridazine hammett equation pK_a lone pair ionization potentials