eng Science and Education Publishing World Journal of Chemical Education 2375-1657 2020-03-07 8 2 61 66 10.12691/wjce-8-2-1 WJCE2020821 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 The strong empirical relation, = (2.4)(2-i), between the Hammett for proton dissociation of several acids and the number, ¡°i¡±, of atoms between the ionizable hydrogen and the ring carbon (Andrew Williams, Free Energy Relationships in Organic and Bioorganic Chemistry, Royal Society of Chemistry, Cambridge, 2003, p. 75) is used to construct a graph for twenty one different proton dissociation equilibriums. The plot of Hammett versus number of atoms i between ionizable hydrogen and the ring carbon atom is observed to be an excellent exponential-decay locus. A good average and intelligent value of Hammett is obtained for the benzene dissociation equilibriums by interpolating the locus of the correlation on to Y-axis. Using this Hammett value and the Hammett equation log [(Ka)X / (Ka)H] = , the pKa value can be calculated for any substituted benzene knowing the pKa value of benzene to be 43. The points for proton dissociation equilibriums of phenylethyl ammonium ions and benzyl alcohols deviated from the graph hence not included in the correlation. Possible explanations are given for deviation of these two equilibriums. http://pubs.sciepub.com/wjce/8/2/1/wjce-8-2-1.pdf attenuation effect linear Free Energy Relationships methylene group acid dissociation equilibriums pK_a of substituted benzenes Andrew Williams¡¯ empirical relation