Electrons in reactions

Assuming that reaction 3 leads also to the same excited state [(CD3)2SOp, Shislov and coworkers13 calculated that the energy of the hot electrons in reaction 3, e is given by... 

The resonance interaction of chlorine with the benzene ring can be represented as shown in 13 or 14, and both of these representations have been used in the literature to save space. However, we shall not use the curved-arrow method of 13 since arrows will be used in this book to express the actual movement of electrons in reactions. We will use representations like 14 or else write out the canonical forms. The convention used in dashed-line formulas like 14 is that bonds that are present in all canonical forms are drawn as solid lines, while bonds that are not present in all forms are drawn as dashed lines. In most resonance, a bonds are not involved, and only the n or unshared electrons are put in, in different ways. This means that if we write one canonical form for a molecule, we can then write the others by merely moving n and unshared electrons. 

Both these conversion processes involve the addition of electrons to the toxic substances. The trichloroethylene molecule is electrically neutral and must gain electrons in reactions that generate negatively charged chloride anions, hi addition, water or hydronium ions must supply hydrogen atoms that replace the chlorine atoms in the organic substance. The detailed reaction is complicated, but the net reaction is relatively simple CI2 C I CHCl + 3 H3 + 6 H2 C CH2 + 3 Cr + 3 H2 O... 

The frontier orbital approach (Fukui et al., 1962, 1954b) has met with considerable success in so far as frontier orbital charges correlate well with experimental data. The performance of these indices is often superior to that of others, with the possible exception of localization energies. It is, however, difficult to give meaning to the correlation since physical interpretations of the role of the frontier electrons in reaction mechanisms are often obscure, and attempts to give substance to Fukui s hypothesis have frequently embodied questionable procedures or models. 

Solution First, we find that 5.585 g of Fe3+ equal 0.100 0 mol of Fe3+. Because each Fe3+ ion requires one electron in Reaction 14-1. 0.100 0 mol of elections must have been transferred. Using the Faraday constant, we find that 0.100 0 mol of electrons corresponds to... 

At pH < 6, in the absende of excess bipy and with EDTA as electron donor, hydrogen production takes place by a different mechanism (reactions 32 to 37 and 39 to 42 for TEOA read EDTA). Presumably, the [Ru(bipy)3]3+ generated in reaction (40) is reduced by EDTA. However, the source of the electron in reaction (41) is unclear, although presumably it could arise from EDTA-formed by deprotonation of EDTA+ in an analogous reaction to that described above for TEOA. 

In turn, such a long-term accumulation of the trapped electrons indicates that the rate of withdrawal of the photogenerated electrons in reaction with water and ethanol in the absence of any additional electron transfer mediator proceeds with a small rate [11, 14]. 

The curved-arrow formalism is universally used for keeping track of the flow of electrons in reactions. We have also used this device (in Section 1-9, for example) to keep track of electrons in resonance structures as we imagined their flow in going from one resonance structure to another. Remember that electrons do not flow in resonance structures they are simply delocalized. Still, the curved-arrow formalism helps our minds flow from one resonance structure to another. We will find ourselves constantly using these (red) curved arrows to keep track of electrons, both as reactants change to products and as we imagine additional resonance structures of a hybrid. 

Positive charge can be stabilized by the nitrogen lone-pair electrons in reaction at both C2 and C3. In reaction at C2, however, stabilization by nitrogen destroys the aromaticity of the fused benzene ring. Reaction at C3 is therefore favored, even though the cationic intermediate has fewer resonance forms, because the aromaticity of the six-membered-ring is preserved. 

This movement of electrons in reactions can be illustrated using curved arrow notation. Because two electron pairs are involved in this reaction, two curved arrows are needed. Two products are formed. 

Curved arrow notation is used extensively to help students follow the movement of electrons in reactions. Where appropriate, mechanisms are presented in parts to promote a better conceptual understanding. 

In chemical reactions electrons move from full to empty orbitals Molecular shape and structure determine reactivity Representing the movement of electrons in reactions by curly arrows... 

Kavan [28] and Kijima et al. [29] have used the electrochemical method to synthesize carbyne. This technique may be realized by classical electrochemistry whereby the charge transfer reaction occurs at interface of a metal electrode and liquid electrolyte solution. Electrons in reaction were supplied either through redox active molecules or through an electrode, which contacts an ionically conducting solid or liquid phase and the precursor. In general, the structure and properties of electrochemical carbon may differ considerably from those of usual pyrolytic carbons. The advantage of this technique is the synthesis of carbyne at low (room) temperature. It was shown that the best product was prepared by cathodic defluorination of poly(tetrafluoroethylene) and some other perhalo-//-alkanes. The carbyne... 

Ions that carry a negative charge are collectively called anions. Nonmetals tend to gain electrons in reactions with metals to form anions. Remember, whether electrons are lost or gained by an atom, the name of the resulting ion is still associated with the name of the element from which it came. Again, only the electrons are involved, not the nucleus. 

Electron-metal+ ion-pairs are more reactive than the free solvated electrons in reactions yielding alkoxide or amides. Apparently, the charge transfer required for the formation of those anions is facilitated by the proximity of Met+ cation which becomes coordinated with the oncomming X-OR reagent. Since, in contrast to liquid ammonia, ion-pairs are the abundant species in organic amine or ether solutions, these directly... 

Such processes are important, for example, in the cytochrome P-450 system. With suitably small reductants, oxygenase activity also has been observed for hemoglobin A. This has led to the characterization of hemoglobin as a frustrated oxidase. Note the format similarity between this process (Equation 4.32) and the bimolecular irreversible oxidation of iron(II) porphyrins the second Fe(II) complex in Reaction (4.29b) functions like the electron in Reaction (4.32). 

Organic chemistry involves reactions between organic compounds and other organic or inorganic species. These reactions can involve both bond-breaking and bond-forming processes, and the key to both is the movement of electrons. Lewis structures provide the bookkeeping system to help us keep track of electrons in reactions. 

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