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| - Barrier Crossing Reaction of Electronically Excited DBMBF2 in n-Nitriles: The Role ofSolvent Polarity on Activation Energy
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| - Solvent viscosity and polarity effects on the picosecond barriercrossing reaction of (dibenzylmethine)boron difluoride in n-nitrile and n-alcoholsolutions have been studied. The hydrodynamic Kramerstheoryyields a poor description of the barrier crossing rates inn-nitriles. Nonlinear isoviscosity plots,solvent-dependent effective potential barrier height, and the anomalous Kramersbehaviour in long-chain n-nitrilessuggest that the transition state is highly polar and the subsequentsolvation effects contribute to the reactionrates. An excellent description of the kinetics is obtained bytaking into account the contribution of thesolvation energy through solute−solvent dipole−dipole interactions.The results suggest that the effectivepotential barrier of the reaction is higher in more polarn-nitriles than in less polar n-nitriles.The dipole−dipole model yields a lower effective potential barrier inn-nitriles than in n-alcohols due toequilibriumsolvation caused by a fast dielectric relaxation of nitriles. Thenovel approach provides an excellentunderstanding of the barrier crossing kinetics of DBMBF2 inn-nitriles and n-alcohols since bothdynamicand static solvation effects are taken into account.
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