Double proton transfer reactions with plateau-like transition state regions: pyrazole-trifluoroacetic acid clusters.
The double proton transfer reactions between carboxylic acids and pyrazole were studied by computational methods up to the coupled-cluster level. Introduction of substituents allowed for a systematic modulation of the reaction profile, resulting in imaginary frequencies of the associated transition states between -1180 and -45 cm(-1). In the latter case, a local transition state is replaced by an extremely flat (plateaulike) transition region, which constitutes the transition from a concerted toward a stepwise mechanism. Vertical excitation energies along the reaction path reveal that the feature of a plateau in the ground state is mirrored in the excited states.
Schweiger
Stefan
S
Institut für Theoretische Chemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
Rauhut
Guntram
G
D006860:Hydrogen Bonding; D008432:Mathematical Computing; D008958:Models, Molecular; D011522:Protons; D011720:Pyrazoles / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics; D014269:Trifluoroacetic Acid / Q000737:chemistry*
D011522:Protons; D011720:Pyrazoles; C031280:pyrazole; D014269:Trifluoroacetic Acid