Temperature effects on the one-electron reduction potentials of nitroaryl compounds

Area of Science:

• Chemical Kinetics
• Electrochemistry
• Radiochemistry

Background:

• One-electron transfer reactions are fundamental in chemistry and biology.
• Viologens and nitroaryl compounds are important redox-active molecules.
• Understanding their redox potentials is crucial for various applications.

Purpose of the Study:

• To establish one-electron transfer equilibria between radical cations of viologens and nitroaryl compounds.
• To investigate the temperature dependence of these redox equilibria.
• To quantify the changes in electron affinity with temperature.

Main Methods:

• Pulse radiolysis was employed to generate radical cations.
• Spectrophotometric detection was used to monitor electron transfer.
• Equilibrium constants were determined in aqueous solutions at pH 8.
• Mid-point reduction potentials were measured across a temperature range (approx. 5-75°C).

Main Results:

• One-electron transfer equilibria were successfully established.
• The difference in reduction potentials (ΔE) between nitro compounds and viologens varied with temperature.
• Increasing temperature decreased the apparent electron affinity of nitroaryl compounds relative to viologens.
• Temperature coefficients (Δ(ΔE)/ΔT) were quantified, ranging from -0.7 to -1.1 mV K⁻¹ at 25°C.

Conclusions:

• Temperature significantly influences the redox properties of nitroaryl compounds.
• Nitroaryl compounds become less electron-affinic relative to viologens at higher temperatures.
• The findings provide valuable thermodynamic data for redox systems involving these compounds.