Directionality and the Role of Polarization in Electric Field Effects on Radical Stability

2017 ◽  
Vol 70 (4) ◽  
pp. 367 ◽  
Author(s):  
Ganna Gryn'ova ◽  
Michelle L. Coote

Accurate quantum-chemical calculations are used to analyze the effects of charges on the kinetics and thermodynamics of radical reactions, with specific attention given to the origin and directionality of the effects. Conventionally, large effects of the charges are expected to occur in systems with pronounced charge-separated resonance contributors. The nature (stabilization or destabilization) and magnitude of these effects thus depend on the orientation of the interacting multipoles. However, we show that a significant component of the stabilizing effects of the external electric field is largely independent of the orientation of external electric field (e.g. a charged functional group, a point charge, or an electrode) and occurs even in the absence of any pre-existing charge separation. This effect arises from polarization of the electron density of the molecule induced by the electric field. This polarization effect is greater for highly delocalized species such as resonance-stabilized radicals and transition states of radical reactions. We show that this effect on the stability of such species is preserved in chemical reaction energies, leading to lower bond-dissociation energies and barrier heights. Finally, our simplified modelling of the diol dehydratase-catalyzed 1,2-hydroxyl shift indicates that such stabilizing polarization is likely to contribute to the catalytic activity of enzymes.

Small ◽  
2018 ◽  
Vol 14 (21) ◽  
pp. 1800365 ◽  
Author(s):  
Congxin Xia ◽  
Wenqi Xiong ◽  
Juan Du ◽  
Tianxing Wang ◽  
Yuting Peng ◽  
...  

Materials ◽  
2003 ◽  
Author(s):  
Subramanian Sankaran ◽  
Jeffrey S. Allen ◽  
Leonard Gumennik

The effect of dc electric fields on destabilization of a vapor microlayer formed during film boiling at various subcooling levels is investigated. High voltage electric fields up to 2000 volts were applied between a 127 μm heater wire and a screen electrode that is concentrically placed at a radius of 25 mm. The qmax and qmin heat fluxes were also measured for the various subcooling and electric field strengths. Up to 50% increase in the qmax and the qmin heat fluxes were observed when using the electric fields in this range of experimental parameters. The relationship among subcooling level for a given fluid, the heat flux level, and the electric field strength required to reach the qmin condition is of interest. The preliminary experimental results and the bubble departure and transition boiling patterns resulting from destabilization of the vapor microlayer are discussed.


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