• Home
  • Search Results
  • Bimolecular electron transfers that deviate from the Sandros-Boltzmann dependence on free energy: steric effect.

Bimolecular electron transfers that deviate from the Sandros-Boltzmann dependence on free energy: steric effect.

The Journal of organic chemistry (2012-01-31)
Pu Luo, Joseph P Dinnocenzo, Paul B Merkel, Ralph H Young, Samir Farid
ABSTRACT

As we reported recently, endergonic to mildly exergonic electron transfer between neutral aromatics (benzenes and biphenyls) and their radical cations in acetonitrile follows a Sandros-Boltzmann (SB) dependency on the reaction free energy (ΔG); i.e., the rate constant is proportional to 1/[1 + exp(ΔG/RT)]. We now report deviations from this dependency when one reactant is sterically crowded: 1,4-di-tert-butylbenzene (C1), 1,3,5-tri-tert-butylbenzene (C2), or hexaethylbenzene (C3). Obvious deviation from SB behavior is observed with C1. Stronger deviation is observed with the more crowded C2 and C3, where steric hindrance increases the interplanar separation at contact by ~1 Å, significantly decreasing the π orbital overlap. Consequently, electron transfer (k(et)) within the contact pair becomes slower than diffusional separation (k(-d)), causing deviation from the SB dependency, especially near ΔG = 0. Fitting the data to a standard electron-transfer theory gives small matrix elements (~5-7 meV) and reasonable reorganization energies. A small systematic difference between reactions of C3 with benzenes vs biphenyls is rationalized in terms of small differences in the electron-transfer parameters that are consistent with previous data. The influence of solvent viscosity on the competition between k(et) and k(-d) was investigated by comparing reactions in acetonitrile and propylene carbonate.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
1,3,5-Tri-tert-butylbenzene, 97%

Social Media

LinkedIn icon
Twitter icon
Facebook Icon
Instagram Icon

MilliporeSigma

Research. Development. Production.

We are a leading supplier to the global Life Science industry with solutions and services for research, biotechnology development and production, and pharmaceutical drug therapy development and production.

© 2021 Merck KGaA, Darmstadt, Germany and/or its affiliates. All Rights Reserved.

Reproduction of any materials from the site is strictly forbidden without permission.