Fine structure in the transition region: reaction force analyses of water-assisted proton transfers.
We have analyzed the variation of the reaction force F(ξ) and the reaction force constant κ(ξ) along the intrinsic reaction coordinates ξ of the water-assisted proton transfer reactions of HX-N = Y (X,Y = O,S). The profile of the force constant of the vibration associated with the reactive mode, k ξ (ξ), was also determined. We compare our results to the corresponding intramolecular proton transfers in the absence of a water molecule. The presence of water promotes the proton transfers, decreasing the energy barriers by about 12 - 15 kcal mol(-1). This is due in part to much smaller bond angle changes being needed than when water is absent. The κ(ξ) profiles along the intrinsic reaction coordinates for the water-assisted processes show striking and intriguing differences in the transition regions. For the HS-N = S and HO-N = S systems, two κ(ξ) minima are obtained, whereas for HO-N = O only one minimum is found. The k ξ (ξ) show similar behavior in the transition regions. We propose that this fine structure reflects the degree of synchronicity of the two proton migrations in each case.
Facultad de Ciencias Exactas, Departamento de Ciencias Químicas, Laboratorio de Química Teórica, Universidad Andres Bello, Av. República 275, Santiago, Chile.
Diana
D
Yepes
Jane S
JS
Murray
Juan C
JC
Santos
Alejandro
A
Toro-Labbé
Peter
P
Politzer
Pablo
P
Jaque
D003198:Computer Simulation; D007700:Kinetics; D015394:Molecular Structure; D011522:Protons; D011789:Quantum Theory; D014867:Water / Q000737:chemistry*
D011522:Protons; D014867:Water