<br/>Bridging the disparate concepts of homogeneous and heterogeneous catalysis remains a challenge in modern chemistry. Towards that end, here we connect the homogeneous chemistry concept of Hammett parameter that quantifies the polarizing capability of a functional group, to the electrochemical concept of polarization induced by a biased electrode used in heterogeneous catalysis. Since molecular polarization is controlled either by functional groups or by an external electrochemical potential, we believe they share similar origins which can be established by experiments and theory. Monitoring the vibrational frequency shift induced by these factors is a suitable experiment to connect the two concepts. Accordingly, first we have measured the nitrile vibrational frequency of 4-R-benzonitrile for a series of polarizing functional groups R spanning a Hammett parameter range -0.83 ≤ σ<sub>p</sub> ≤ +1.11. The Hammett parameter of the R group affects the molecular polarization which in turn influences the nitrile stretch frequency. Second, using vibrational sum frequency generation spectroscopy, we have measured the nitrile stretch frequency of 4-mercaptobenzonitrile adsorbed on a gold electrode as a function of polarizing potentials from -1.4 V to +0.6 V vs Ag/AgCl. By comparing the nitrile stretch frequency in these two experiments, we found a correlation between the Hammett parameter, and the local electric field at the electrode interface. This correlation allows us to think of a polarizing electrode as a functional group. The experimental findings are backed by computational work. We envision our work will serve as a Rosetta stone connecting the realms of homogeneous and heterogeneous chemistry.<br/>

Electrodes as polarizing functional groups: Correlation between Hammett parameters and electrochemical polarization

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.