Definition of oxidation reaction
This is a very unsatisfactory definition because many oxidation-reduction or redox reactions do not involve changes in hydrogen or oxygen content, as the following example illustrates:
Redox reactions or oxidation-reduction of organic compounds are better defined in terms of the concept of electron transfer. Thus an atom is said to be oxidized if, as the result of a reaction, it experiences a net loss of electrons; and is reduced if it experiences a net gain of electrons. This simple definition can be used to identify oxidation-reduction of organic compounds at carbon in terms of a scale of oxidation states for carbon based on the electronegativities of the atoms attached to carbon. The idea is to find out whether in a given reaction carbon becomes more, or less, electron-rich. We will use the following somewhat arbitrary rules:
1. Elementary carbon is assigned the zero oxidation state.
2. The oxidation state of any chemically bonded carbon may be assigned by adding —1 for each more electropositive atom and +1 for each more electronegative atom, and 0 for each carbon atom bonded directly to the carbon of interest (see Figure 10-11 for the Pauling electronegativity scale). That is,
—1 for electropositive atoms, H, B, Na, Li, Mg
+ 1 for electronegative atoms, halogens, O, N, S 0 for carbon.
The rationale for this mode of operation can be seen if we look more closely at the example of CH3Cl + Mg—–> CH3—Mg—Cl. Chlorine is more electronegative than either carbon or magnesium. Carbon is more electronegative than magnesium. Thus CH3Cl is written properly with a polar bond as
CH3 —–Cl, whereas the C-Mg bond is oppositely polarized, CH3—–Mg. If all of the bonds were ionized completely, we could write
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