Electron rearrangement

The operation time scale of molecular devices [point (iv)] can range from less than picoseconds to seconds, depending on the type of rearrangement (electronic or nuclear) and the nature of the components involved. 

The carbonium ion now being unstable, if not stabilized by resonance or by hyperconjugation, rearranges electronically to split out a proton, which is ready to repeat the process at another electron-rich point. 

Chen, J.C.Y. (1966). Dissociative attachment in rearrangement electron collision with molecules, Phys. Rev. 148, 66-73. 

In Baeyer-Villiger rearrangements electron-rich aryl groups migrate faster than H-atoms, and H atoms in turn migrate faster than electron-poor aryl groups. Aldehydes,... 

McLafferty rearrangement. Electron-impact-induced cleavage of carbonyl compounds having a hydrogen in the y-position, to an enolic fragment and an olefin. 

Rearrangements Compete with Sn2 and Sn1 Rearrangement Electron Flow Paths 1, 2R and 1,2RL Approaches to Rearrangement Mechanisms Summary... 

Note that one oxygen atom is bound to the heme iron and one oxygen atom is associated with Cub. This reaction is a rapid four-electron reduction of O2, bypassing any formation of toxic reactive oxygen species (superoxide, peroxide, hydroxide radical) (see Babcock ). Even though the Fe" " =0 state and Tyr radical that are formed at the catalytic site are reactive, they are bound to the COX and are not released. Note that the formation of Pm just rearranges electrons and protons that are already present at the catalytic site and does not require any additional proton or electron input. 

The reactivity of the excited species will be influenced by both its energy level and rearranged electron configuration. Excited species are usually both better electron donors and electron acceptors than their parent molecules. The excited electron would be more readily donated while the low-energy vacancy left by the excited electron would more readily accept an electron. The redistribution of electrons in molecular orbitals may influence shape and dipole moments. Hydrogen abstraction is a common reaction of excited species. For example, benzophenone in the presence of a suitable donor solvent such as ethanol is readily reduced to the alcohol. 

The simplest case corresponds to the one-electron transfer between the electrode and species that are chemically stable on the time scale of the experiments (Eq. (1.1)). However, electrochemical systems are frequently more complicated and the electroactive species take part in successive electron transfer reactions at the electrode (multistep processes) and/or in parallel chemical reactions in solution such as protonation, dimerisation, rearrangement, electron exchange, nucleophilic/electrophilic addition, disproportionation, etc., the product(s) of which may or may not be electroactive in the potential region under study. The simulation of these cases is described in Chapters 5 and 6. 

The analytical methods that employ this technique, such as mass spectrometry, typically study the properties of the molecular ions themselves rather than the electrons that were removed. The two processes are related, however, because the energies observed for one technique are often identical to those observed for the other. This can be understood at a rudimentary level by considering the law of conservation of energy as it must apply to the overall process of rearrangement. Electrons move from one orbital to another after one has been removed from an inner orbital and rearrangement of the electron distribution takes place to fill in the hole. ... 

Chemical reactions involve cross-linking, degradation, and rearrangement. Electronic energy transfer involves exothermic processes, where part of the energy is absorbed as heat, and part is emitted via fluorescence or phosphorescence from the donor molecule. 

Fig. 17. A schematic representation for the generation of a neutral soliton-antisoliton pair in PA. (a) trans-PA. (b) TWo electrons were promoted from the valence band to the conduction band via either thermal or photochemical means, (c) Chain relaxation rearranges electrons to the midgap energy level, (d) Rearrangement induces bond alterations between single electrons.

The insertion of isocyanates into C-H bonds is also well known. Olefins, alkanes, aromatic and heteroaromatic compounds are known to react with isocyanates to give N-substituted carboxylic acid amides. Often the formation of the linear adduct is the result of a [2+2] cycloaddition reaction and subsequent rearrangement. Electron donating groups on the aromatic nucleus on the one side and electron withdrawing groups on the isocyanate enhance the reactivity of both components. Lewis acids, such as aluminum chloride, are supplied successfully as catalysts... 

A Lewis acid has an empty orbital (or can rearrange electrons to create an empty orbital) that can accept an electron pair. 

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