Table 1. pKa values of pyridinium and phosphorinium ions and Hammett values for the three equilibriums

From

Comparison of Substituent Effects in Benzenes (XC5H5C), Pyridines (XC5H4N) and Phosphorines (XC5H4P) and their Protonated Species

R. Sanjeev, V. Jagannadham

World Journal of Chemical Education. 2020, 8(4), 155-162 doi:10.12691/wjce-8-4-3