| Abstract
| - Second-order rate constants and equilibrium constantshave been determined for the benzoate ionpromoted deprotonation reactions of(m-nitrophenyl)nitromethane,(p-nitrophenyl)nitromethane,and (3,5-dinitrophenyl)nitromethane in methanol solution. ThepKa values for the arylnitromethanes in methanol are the following: pKa= 10.9, 10.5, and 9.86 for(m-nitrophenyl)nitromethane, (p-nitrophenyl)nitromethane, and(3,5-dinitrophenyl)nitromethane, respectively,relative to benzoic acid (pKa = 9.4). ABronsted βB value of 0.50 and αCH value of1.31 have beencalculated for the 3,4-dimethylbenzoate, benzoate,m-bromobenzoate, and 3,4-dichlorobenzoate ionpromoted reactions of (3,5-dinitrophenyl)nitromethane, and for thebenzoate ion promoted reactionsof (m-nitrophenyl)nitromethane,(p-nitrophenyl)nitromethane, and(3,5-dinitrophenyl)nitromethane,respectively. The log of the intrinsic rate constants for benzoateion promoted deprotonations of(m-nitrophenyl)nitromethane,(p-nitrophenyl)nitromethane, and(3,5-dinitrophenyl)nitromethaneare 0.0212, 0.270, and 0.877, respectively. These values are 6.3× 104, 2.0 × 104, and 2.5 ×104times lower than for the same reactions in acetonitrile solution.The transfer activity coefficientfrom methanol to acetonitrile solution, logMγAN, for(m-nitrophenyl)nitromethyl anion (3.6) and(m-nitrophenyl)nitromethane (−1.0) have beencalculated. The solvent effect on these reactionsin methanol and acetonitrile, two solvents with similar dielectricconstants, are analyzed withinthe framework of the Principal of Nonperfect Synchronization. Theresults suggest that the observedsolvent effect is a result of an imbalanced transition state(i.e., PNS effects), and a strongertransitionstate hydrogen bond between the carbon acid and benzoate ion inacetonitrile than in methanolsolution.
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