In this Account we have compiled a list of reliable bond energies that are based on a set of critically evaluated experiments. A brief description of the three most important experimental techniques for measuring bond energies is provided. We demonstrate how these experimental data can be applied to yield the heats of formation of organic radicals and the bond enthalpies of more than 100 representative organic molecules.

Bond Dissociation Energies of Organic Molecules

▪ Abstract Proton-coupled electron transfer (PCET) is an important mechanism for charge transfer in a wide variety of systems including biology- and materials-oriented venues. We review several are...

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Proton-Coupled Electron Transfer

The miniaturization of components used in the construction of working devices is being pursued currently by the large-downward (top-down) fabrication. This approach, however, which obliges solid-state physicists and electronic engineers to manipulate progressively smaller and smaller pieces of matter, has its intrinsic limitations. An alternative approach is a small-upward (bottom-up) one, starting from the smallest compositions of matter that have distinct shapes and unique properties-namely molecules. In the context of this particular challenge, chemists have been extending the concept of a macroscopic machine to the molecular level. A molecular-level machine can be defined as an assembly of a distinct number of molecular components that are designed to perform machinelike movements (output) as a result of an appropriate external stimulation (input). In common with their macroscopic counterparts, a molecular machine is characterized by 1) the kind of energy input supplied to make it work, 2) the nature of the movements of its component parts, 3) the way in which its operation can be monitored and controlled, 4) the ability to make it repeat its operation in a cyclic fashion, 5) the timescale needed to complete a full cycle of movements, and 6) the purpose of its operation. Undoubtedly, the best energy inputs to make molecular machines work are photons or electrons. Indeed, with appropriately chosen photochemically and electrochemically driven reactions, it is possible to design and synthesize molecular machines that do work. Moreover, the dramatic increase in our fundamental understanding of self-assembly and self-organizational processes in chemical synthesis has aided and abetted the construction of artificial molecular machines through the development of new methods of noncovalent synthesis and the emergence of supramolecular assistance to covalent synthesis as a uniquely powerful synthetic tool. The aim of this review is to present a unified view of the field of molecular machines by focusing on past achievements, present limitations, and future perspectives. After analyzing a few important examples of natural molecular machines, the most significant developments in the field of artificial molecular machines are highlighted. The systems reviewed include 1) chemical rotors, 2) photochemically and electrochemically induced molecular (conformational) rearrangements, and 3) chemically, photochemically, and electrochemically controllable (co-conformational) motions in interlocked molecules (catenanes and rotaxanes), as well as in coordination and supramolecular complexes, including pseudorotaxanes. Artificial molecular machines based on biomolecules and interfacing artificial molecular machines with surfaces and solid supports are amongst some of the cutting-edge topics featured in this review. The extension of the concept of a machine to the molecular level is of interest not only for the sake of basic research, but also for the growth of nanoscience and the subsequent development of nanotechnology.

Artificial Molecular Machines.

Tetrathiafulvalenes, oligoacenenes, and their buckminsterfullerene derivatives: the brick and mortar of organic electronics.

Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate properties of materials and electrode reactions. This Primer provides a guide to the use of EIS with a comparison to other electrochemical techniques. The analysis of impedance data for reduction of ferricyanide in a KCl supporting electrolyte is used to demonstrate the error structure for impedance measurements, the use of measurement and process models, as well as the sensitivity of impedance to the evolution of electrode properties. This Primer provides guidelines for experimental design, discusses the relevance of accuracy contour plots to wiring and instrumentation selection, and emphasizes the importance of the Kramers-Kronig relations to data validation and analysis. Applications of EIS to battery performance, metal and alloy corrosion, and electrochemical biosensors are highlighted. Electrochemical impedance measurements depend on both the mechanism under investigation and extrinsic parameters, such as the electrode geometry. Experimental complications are discussed, including the influence of nonstationary behaviour at low frequencies and the need for reference electrodes. Finally, emerging trends in experimental and interpretation approaches are also described.

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Electrochemical Impedance Spectroscopy

International consensus report on diagnosis and treatment of asthma.

L'etude est faite par voltammetrie cyclique en solution aqueuse a pH 9,2 dans laquelle le ferrocene est present sous forme d'anion ferrocenecarboxylate

Electron-Transfer Reactions Associated with Host-Guest Complexation. Oxidation of Ferrocenecarboxylic Acid in the Presence of β-Cyclodextrin

Certainly one of the first topics to come to mind on seeing the term “molecular electrochemistry” is the subject of electron-transfer reactions. In most cases, a multistep electrode reaction will be initiated by an electron-transfer step, either gain or loss of an electron. The product of that reaction will subsequently participate in chemical and electrochemical reactions leading finally to the end product of the reaction. Thus, an understanding of electron transfer is basic to the entire field of molecular electrochemistry. For a majority of electrode reactions of organic and organometallic species, only a single oxidation or reduction is encountered within the accessible potential range of the solvent/electrolyte medium that is chosen. This is often because that single electron transfer is situated fairly close to the solvent breakdown potential so that second or subsequent electron transfers are masked. However, in many instances two separate electron-transfer reactions can be detected with the normal pattern being that addition or removal of the second electron occurs with greater difficulty than the first. In many of these cases, but not all, the molecule contains two identical electroactive groups, an example being the reduction of dinitroaromatics such as 1,4-dinitrobenzene.

One-electron and two-electron transfers in electrochemistry and homogeneous solution reactions.

Although the reactions of lithium and Grignard reagents with buckminsterfullerene (C{sub 60}) forming alkylated or arylated products have been reported, no structurally well-defined anionic products has been isolated. The compounds (R{sub 3}P){sub 2}M({eta}{sup 2}-C{sub 60}) (M=Ni,Pd,Pt) were 0.36 V harder to reduce than C{sub 60}, indicating that the electron affinity and reactivity of the C{sub 60} cluster toward nucleophiles is reduced. We reasoned that addition of a single alkyl anion to produce RC{sub 60}{sup -} should be possible. Here we report the synthesis and properties of the tert-butyllithium adduct of C{sub 60} isolated in impure form as t-BuC{sub 60}{sup -}Li{sup +}{center_dot}3-4THF(1a), and in pure form as t-BuC{sub 60}{sup -}Li{sup +}{center_dot}4CH{sub 3}CN(1b). Protonation of 1b yields a mixture of isomers of t-BuC{sub 60}H (2a and 2b) with 2a converting to 2b over time. The compound t-BuC{sub 60}H is one of the strongest acids made up of only carbon and hydrogen and has a relatively weak C{sub 60}-H bond. 14 refs., 1 fig.

Dennis H. Evans

Papers

International consensus report on diagnosis and treatment of asthma.

Electron-Transfer Reactions Associated with Host-Guest Complexation. Oxidation of Ferrocenecarboxylic Acid in the Presence of β-Cyclodextrin

One-electron and two-electron transfers in electrochemistry and homogeneous solution reactions.

Synthesis, chemistry, and properties of a monoalkylated buckminsterfullerene derivative, tert-BuC60 anion

Acquisition and analysis of cyclic voltammetric data