Electrostatic Catalysis of Proton-Transfer Reactions: Hydrogen Exchange in Chloroform and Ionization of 2-Nitropropane

Article abstract of DOI:10.1021/ja00354a033

Rates of detritiation of chloroform-t catalyzed by a series of ω-trimethylammonioalkylamines, (CH3)3N⁺(CH2)nNH2 with n = 3-5, were measured in aqueous solution at 25 deg C, and rates of ionization of 2-nitropropane catalyzed by the same amines with n = 2-5, four additional uncharged primary amines, two aminocarboxylate ions, and ethylenediamine and its monoprotonated conjugate acid were also measured.The uncharged primary amines give a good Broensted correlation for the nitroalkane ionization, with β = 0.61 +/- 0.03; the positively charged catalysts show positive deviation from this correlation and the negatively charged catalysts show negative deviations.The ω-trimethylammonioalkylamines also give positive deviations from a previously constructed Broensted correlation for the chloroform detritiation reaction; the latter deviations are much larger than the corresponding ones for 2-nitropropane ionization, which is consistent with the greater developement and concentration of charge in the transition state of the chloroform reaction.The pattern of electrostatic effects provided by these results indicates a field rather than an inductive mechanism for transmission of the polar interaction.