Electron three-stage

A number of reaction pathways have been proposed for the Fischer indolization reaction. The mechanism proposed by Robinson and Robinson in 1918, which was extended by Allen and Wilson in 1943 and interpreted in light of modem electronic theory by Carlin and Fischer in 1948 is now generally accepted. The mechanism consists of three stages (I) hydrazone-ene-hydrazine equilibrium (II) formation of the new C-C bond via a [3,3]-sigmatropic rearrangement (III) generation of the indole nucleus by loss of... 

The integration of PS I and PS II in chloroplasts occurs as shown in Figure 7.10 [37,39]. The overall reaction of the transfer of electrons starting from water takes place in three stages. 

The metabolic machinery responsible for the heterotrophic respiration reactions is contained in specialized organelles called mitochondria. These reactions occur in three stages (1) glycolysis, (2) the Krebs or tricarboxylic acid cycle, and (3) the process of oxidative phosphorylation also known as the electron transport chain. As illustrated in... 

Fluorescence is a three-stage process excitation via the absorption of a radiation, excited state for a very short time -(10 9 sec), and emission. The excitation of a molecule is achieved by the absorption of a light quantum of an appropriate wavelength, promoting, in a simplified view, a ir or nonbonding (n) electron to a 7r antibonding orbital. The quantum yield is a fundamental molecular property that describes the ratio of the number of emitted photons to the number of photons absorbed. 

In the case of ester hydrolysis the O of the water is an electron-rich substance and the carbonyl carbon of the ester is an electron-deficient substance. Ester hydrolysis occurs in three stages (1) the initial stage in which electrons flow from the water molecule to the ester (2) the intermediate stage in which the ester carbonyl forms a tetrahedral complex involving the hydroxyl group originating from the water molecule that releases a proton and (3) the final stage in which carboxylic acid and alcohol are formed. 

Electron transfer reactions have been characterized with much more rigor in inorganic chemistry than with organic molecules. Marcus has provided the principal description relating the kinetics and thermodynamics of electron transfer between metal complexes (1). The Marcus theory, a computationally simple approach with good predictive power, is an empirical treatment which uses thermodynamic parameters and spectroscopic measurements to calculate kinetic data. It assumes that bimolecular electron transfer reactions occur in three stages as shown in Scheme 1 (1) formation of the precursor complex, (2) electron transfer, and (3) solvation of the redox pair. 

Near the resonances the cross section of vibrational excitation increases by several orders of magnitude. From the physical standpoint we can divide each resonance process into three stages. At the first stage the incident electron is captured by the electron shell of the molecule, forming an intermediate negative molecular ion. The second stage is the vibrational motion of the nuclei of the newly formed ion, which eventually leads to the third stage of the process—the decay of the intermediate ion. 

The change of electronic conductivity G(r) over diameter of such two-sphere model composition as element in a system of contacting particles is shown in a Figure 10.6b. The transfer of electron across this composition consists of three stages electron tunneling over the interspace — Rq is replaced by the M/SC conductivity across a particle with subsequent electron tunneling over the further interspace R — Rq. The probability of electron tunneling falls down exponentially with increase in distance from the surface of particle. 

Let us compare the probabilities of tunnel electron transfer from singly and doubly charged metallic nanoparticles (Z — —l and Z = —2) to an adsorbed molecule. In the general case, tunnel electron transfer occurs in three stages (i) thermal activation of an electron in the metal, (ii) tunneling of the electron through the barrier to a molecular level, and (iii) transformation of the adiabatic potential of the molecule. 

Figure 5-1. Schematic representation of the three stages of photosynthesis in chloroplasts (1) The absorption of light can excite photosynthetic pigments, leading to the photochemical events in which electrons are donated by special chlorophylls. (2) The elections are then transferred along a series of molecules, causing the oxidized form of nicotinamide adenine dinucleotide phosphate (NADP+) to become the reduced form (NADPH) ATP formation is coupled to the electron transfer steps. (3) The biochemistry of photosynthesis can proceed in the dark and requires 3 mol of ATP and 2 mol of NADPH per mole of C02 fixed into a carbohydrate, represented in the figure by (CH20).

In 1967, the first three-stage electron-transfer process examined by pulse radiolysis was reported [67], Such a cascade process is of relevance to electron transport in biological systems. By irradiating an aqueous solution containing acetone (0.82 mol dm ), acetophenone (3.34 mmol dm ), and benzophenone (72 pmol dm ) at pH 13, Adams et al. [67] were able to observe, at 2 ps after the pulse, the spectrum of the acetophenone radical anion (2max 445 nm, max 260 m mol ) [68] originating from the reduction of acetophenone by the (CH3)2CO radical. In the following 50 ps, the acetophenone radical anion reacted with benzophenone k — 7.8 X 10 dm mol" s ) so that the absorption band at 445 nm disappeared... 

Marcus [12-14] provided a simple approach allowing the prediction of the kinetics of the process, using thermodynamic parameters and spectroscopic measurements. Marcus theory assumes that bimolecular electron transfer, as shown in Scheme 1, occurs in three stages ... 

Chain polymerization involves three stages initiation, propagation, and termination. The most important of the chain polymerization methods is free radical polymerization, in which the initiation step occurs by an attack on the monomer molecule by a free radical. A free radical is a reactive molecule possessing an unpaired electron and is usually formed by the decomposition of a relatively unstable molecule referred to as an initiator. In particular, those compounds containing peroxide bonds, (—O— O—), can produce free radicals by thermal decomposition, for example,... 

Electrociystallization denotes nucleation and crystal growth in electrochemical sterns under the influence of an electric field [1.1-1.21]. Electrocrystallization of metals takes place at an electronic conducting substrate / ionic conducting electrolyte interface including, in general, three stages ... 

The transfer of electrons from NADH to 02 occurs in three stages, each of which involves a large protein complex in the inner mitochondrial membrane. 

Bimolecular electron transfer "" occurs in three stages ... 

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