Different substituents for these two compounds are in column ii. The corresponding Hammett plots are given in figure and figure . The pKaH+ data is available in 5% aqueous ethanol at 30 o C for nine substituted benzimidazolium cations at position 2. A Taft plot is presented in figure . The data corresponds to the columns xiii, xiv and xv of table 1. The point of the branched chain substituent i-Pr which may cause steric effect and the points of the substituents CH(OH)CH3, COCH3, and CF3 capable of forming hydrogen bonding as shown in scheme 4, scheme 5, and scheme 6 are deviating from the Taft correlation (figure ).