Acid ionization in aprotic media is studied using molecular dynamics techniques. In particular, models for HCl ionization in acetonitrile and dimethylsulfoxide are investigated. The proton is treated quantum mechanically using Feynman path integral methods and the remaining molecules are treated classically. Quantum effects are shown to be essential for the proper treatment of the ionization, The potential of mean force is computed as a function of the ion pair separation and the local solvent structure is examined. The computed dissociation constants in both solvents differ by several orders of magnitude which are in reasonable agreement with experimental results. Solvent separated ion pairs are found to exist in dimethylsulfoxide but not in acetonitrile. Dissociation mechanisms in small clusters are also investigated. Solvent separated ion pairs persist even in aggregates composed of rather few molecules, for instance, as few as 30 molecules, For smaller clusters or for large ion pair separations cluster finite-size effects come into play in a significant fashion.
Molecular dynamics study of solvation effects on acid dissociation in aprotic media / Laria, D; Kapral, R; Estrin, D; Ciccotti, Giovanni. - In: THE JOURNAL OF CHEMICAL PHYSICS. - ISSN 0021-9606. - 104:(1996), pp. 6560-6568. [10.1063/1.471375]
Molecular dynamics study of solvation effects on acid dissociation in aprotic media
CICCOTTI, Giovanni
1996
Abstract
Acid ionization in aprotic media is studied using molecular dynamics techniques. In particular, models for HCl ionization in acetonitrile and dimethylsulfoxide are investigated. The proton is treated quantum mechanically using Feynman path integral methods and the remaining molecules are treated classically. Quantum effects are shown to be essential for the proper treatment of the ionization, The potential of mean force is computed as a function of the ion pair separation and the local solvent structure is examined. The computed dissociation constants in both solvents differ by several orders of magnitude which are in reasonable agreement with experimental results. Solvent separated ion pairs are found to exist in dimethylsulfoxide but not in acetonitrile. Dissociation mechanisms in small clusters are also investigated. Solvent separated ion pairs persist even in aggregates composed of rather few molecules, for instance, as few as 30 molecules, For smaller clusters or for large ion pair separations cluster finite-size effects come into play in a significant fashion.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.