A comparison of substituent effects on the proton and carbon basicities of thiophenoxide ions

A comparison is made of the effects of substituents on the proton and carbon basicities of thiophenoxide ions. The carbon basicities were determined by measurements of the equilibrium constants for formation of 1 : 1 covalently bound addition complexes of the thiophenoxides with 1,3,5-trinitrobenzene. They show a somewhat greater susceptibility to change in substituent than do the proton basicities although the general behaviour pattern is similar. The correlation of the substituent effects by σ° values is discussed.