Acid−Base Properties of Fulleropyrrolidines:  Experimental and Theoretical Investigations

The acid−base equilibria of 2-(n-alkyl)fulleropyrrolidines and N-methyl-2-(n-alkyl)fulleropyrrolidines in aqueous micellar media of a sodium dodecyl sulfate surfactant are examined experimentally and modeled theoretically by using ab initio 3-21G(*) methods. The pKa values, for 2-(n-alkyl)fulleropyrrolidines and N-methyl-2-(n-alkyl)fulleropyrrolidines, determined both by HCl and NaOH titration with potentiometric detection of the end point, are equal to 6.3 ± 0.1 and 7.5 ± 0.1, respectively, and are independent of the alkyl chain length within a range of C1 to C8. The obtained results indicate that the fullerene cage fused to a pyrrolidine ring increases the acidity of the protonated pyrrolidine nitrogen mainly due to the induced electronic effects and, to a smaller extent, by structural effects. The 3-21G(*) estimated free energy difference, ΔE (with solvation corrections incorporated based on the Cramer-Truhlar SM5.4 solvation model), between the protonated and unprotonated fulleropyrrolidines, and the ...