Oxidation state or number

The following are few simple rules for determining the oxidation state or number of elements in chemical reactions (Madigan and Martinko, 2006). 

The oxidation state of C in simple compounds can be calculated by adding the oxidation numbers of the O and H atoms present in the compound. According to rule number 4, the sum of all oxidation numbers must equal to 0. For example, the oxidation state of C in COj can be determined as follows 0(-2 X 2 = -4) + C(+4) = 0. 

In organic compounds, it may not be possible to assign a specific oxidation number for C atoms, but the oxidation state of a whole compound can be calculated. For example, the oxidation state of C in the glucose molecule CgHi206 is 0, because 60 at -2 = -12 and 12H+ at +1 = +12. 

---

Fig.1. Structures of porphyrin 1, chlorophyll 2, and phthalocyanine 3. In the presence of metal salts M"+X (M=metal, X=counter anion, n=oxidation state or number of counter anions), porphyrins produce chelate complexes. Some metal chelates of the porphyrins, such as ZnPor, form further coordination bonds with other ligands such as pyridines...

FeO4 (ferrate) and Fe(catecholate)3 the covalence of iron is six and for Fe(CO)5 the covalence of iron is eight. In each of these compounds the iron atom is uncharged and has eight valence electrons (3d 4s2 —> d sp -> d sp. For these examples, the traditionally used formal oxidation states of iron [II, III, IV, VI, and VIII (or 0), respectively] are the same as their covalences (number of covalent bonds). However, the iron in (porphyrin)Fe( "> (OH2) (d5sp2) has a covalence of three, a formal oxidation state of three, and a charge of 1-t- via the covalently bound H2O. In the present discussion Roman numeral superscripts associated with the metals in the formulas for their compounds and complexes indicate their covalence (number of covalent bonds), not their oxidation state or number. 

It uses classical ideas and language that are common to all chemists, such as electronegativity or Lewis structures for the ligands. It provides important information, such as the oxidation state (or number) of the metal in the complex, the number of electrons in tbe immediate environment of tbe metal, and wbat one normally calls tbe electronic configuration of the complex. 

Plan First, we assign oxidation states, or numbers, to all the atoms and determine which elements change oxidation state. Second, we apply the definitions of oxidation and reduction. 

INTRODUCTION AND SECTION 20.1 In this chapter we have focused on electrochemistry, the branch of chemistry that relates electricity and chemical reactions. Electrochemistry involves oxidation-reduction reactions, also called redox reactions. These reactions involve a change in the oxidation state of one or more elements. In every oxidation-reduction reaction one substance is oxidized (its oxidation state, or number, increases) and one substance is reduced (its oxidation state, or number, decreases). The substance that is oxidized is referred to as a reducing agent, or reductant, because it causes the reduction of some other substance. Similarly, the substance that is reduced is referred to as an oxidizing agent, or oxidant, because it causes the oxidation of some other substance. 

Actinide ions form complex ions with a large number of organic substances (12). Their extractabiUty by these substances varies from element to element and depends markedly on oxidation state. A number of important separation procedures are based on this property. Solvents that behave in this way are thbutyl phosphate, diethyl ether [60-29-7J, ketones such as diisopropyl ketone [565-80-5] or methyl isobutyl ketone [108-10-17, and several glycol ether type solvents such as diethyl CeUosolve [629-14-1] (ethylene glycol diethyl ether) or dibutyl Carbitol [112-73-2] (diethylene glycol dibutyl ether). 

The concept of the oxidation state of an element in a chemical compound has a long and confusing history. In the most pretentious form of the concept the oxidation state or oxidation number is the electrical charge localised on the concerned atom in the compound. Confusion arises when we realise that the definition of the atomic domain is arbitrary and the experimental determination of the electrical charge in the once chosen domain is often problematic. 

In this review the oxidation state or oxidation number will be used in this formal sense, unless otherwise stated. ... 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

The oxidation state of an element in a compound is an indication of how many electrons each atom of that element has lost (positive oxidation state) or gained (negative). Since oxidation state is determined by a set of rules, rather than by experiment, its connection to the number of electrons actually transferred is rather tenuous. It is used in naming compounds and balancing some chemical equations. 

Copper(I) catalysis is very well established to promote intramolecular [2+2] photocycloaddition reactions of l,n-dienes (review [351]). The methodology recently enjoyed a number of applications [352-354], It is assumed that CuOTf, which is commonly applied as the catalyst, coordinates the diene and in this way mediates a preorganization. The Ghosh group recently reported a number of CuOTf-catalyzed photochemical [2+2] cycloaddition reactions, in which an organocopper radical complex was proposed as a cyclization intermediate (which should, however, have a formal Cu(II) oxidation state) (selected references [355-357]). A radical complex must, however, not be invoked, since the process may either proceed by a [2+2] photocycloaddition in the coordination sphere of copper without changing the oxidation state or according to a cycloisomerization/reductive elimination process. 

---