Research

 

Electron Transfer Initiated Reactions

 

Sticky dissociative ET in The electrochemical reduction of p-substituted arene sulfonyl chlorides
Sticky dissociative ET in The electrochemical reduction of p-substituted arene sulfonyl chlorides
(A. Houmam and E. M. Hamed, PhysChemChemPhys. 2012, 14, 113)
Electron transfer reactions are among the most elementary of all chemical reactions and play a fundamental role in many areas including organic synthesis, biological processes, novel energy sources, energy storage devices, amperometric sensors, etc. A field that has attracted considerable attention is that involving electron transfer to organic and bioorganic molecules. In such reactions, electron transfer is very often accompanied by the formation of new chemical bonds and/or the dissociation of existing ones. A wide variety of chemical transformations that are initiated by a single initial electron transfer are described in the literature and can be encountered under both oxidative and reductive conditions. Unravelling the nature of the fundamental steps involved in the electron transfer and the subsequent reactions has always been an essential step towards reaching a molecular understanding of these processes. In these multiple step reactions important questions arise not only concerning their mechanisms and the factors controlling them but also the associated energies and kinetics and any similarity to certain non-electron transfer processes. Extensive studies have already shed considerable new light on many of these important questions.

 

Dissociation mechanisms of p-substituted arene sulfenonyl phthalimide radical anions
Dissociation mechanisms of p-substituted arene sulfenonyl phthalimide radical anions
(A. Houmam and E. M. Hamed, Chem. Commun. 2012, 48, 11328)
Considerable progress has been achieved in understanding electron transfer initiated bond formation and/or bond breaking reactions. From a mechanistic standpoint, the electron transfer step in these reactions can be classified into two main pathways. In the first mechanism, the bond formation or dissociation occurs subsequent to the initial electron transfer process, and involves either an oxidized or a reduced species of the parent substrate that only undergoes a degree of reorganization and no bond disruption. In the second mechanism the electron transfer is associated with a simultaneous bond cleavage. Progress made in the fundamental understanding of electron transfer processes has not only made it possible, to distinguish between processes associated with different degrees of reorganization, but also to account for the structural changes involved. It has also allowed distinction to be made between processes involving different degrees of donor-acceptor interactions in the transition states.

 

Electrochemical reduction of p-nitrophenyl sulfenyl chloride: Cyclic voltammogram, potential energy variation and LUMO and SOMOs structures of neutral and reduced species
Electrochemical reduction of p-nitrophenyl sulfenyl chloride: Cyclic voltammogram, potential energy variation and LUMO and SOMOs structures of neutral and reduced species (C. Ji; M. Ahmida; M. Chahma and A. Houmam, J. Am. Chem. Soc. 2006, 128, 15423)

The ability to unravel the more intricate details of electron transfer reactions has greatly benefited from the widespread interest that the chemistry of reactive intermediates including radicals, ions and radical ions has attracted in recent decades. The considerable amount of experimental and theoretical data concerning these reactive intermediates that has become available has allowed a more accurate analysis of the dynamics of such electron reactions.

 

Our research group is interested in all aspects related to electron transfer initiated chemical reactions. Particular attention is given to understanding the mechanisms, kinetics and thermodynamics of the studied reactions, and the factors controlling them. The investigated organic compounds are particularly chosen based on specific functional groups and on their potential use in organic synthesis and as precursors for surface modification and materials synthesis. These compounds are usually synthesized and then investigated using a series of electrochemical and photochemical techniques including cyclic voltammetry, convolution analysis, electrolysis, laser flash photolysis, etc. The products are extracted and are analyzed using techniques such as HPLC, GCMS, NMR spectroscopy, etc. Analysis of the data is done through application of the fundamental electron transfer theories.

 

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