Molecular oxygen unpaired electrons

Molecular oxygen contains two unpaired electrons and has the distinction of being capable of both initiating and inhibiting polymerization. It functions in the latter capacity by forming the relatively unreactive peroxy radical ... 

As shown in Fig. 12-6, hydroxyl radicals primarily add to either of the carbon atoms which form the double bond. The remaining carbon atom has an unpaired electron which combines with molecular oxygen, forming an RO2 radical. There are two types of RO2 radicals labeled C3OHO2 in Fig. 12-6. Each of these RO2 radicals reacts with NO to form NO2, and an alkoxy radical reacts with O2 to form formaldehyde, acetaldehyde, and HOj. 

The presence of oxygen can modify the course of a fiee-radical chain reaction if a radical intermediate is diverted by reaction with molecular oxygen. The oxygen molecule, with its two unpaired electrons, is extremely reactive toward most free-radical intermediates. The product which is formed is a reactive peroxyl radical, which can propagate a chain reaction leading to oxygen-containing products. 

This could account for the paramagnetism, but esr evidence shows that the 2 cobalt atoms are actually equivalent, and X-ray evidence shows the central Co-O-O-Co group to be planar with an 0-0 distance of l3l pm, which is very close to the 128 pm of the superoxide, 02, ion. A more satisfactory formulation therefore is that of 2 Co atoms joined by a superoxide bridge. Molecular orbital theory predicts that the unpaired electron is situated in a rr orbital extending over all 4 atoms. If this is the case, then the jr orbital is evidently concentrated very largely on the bridging oxygen atoms. 

Sulfonyl radicals are often represented simply as XS02 where the sulfur atom is understood to be bonded to two oxygens as well as to X the moiety X may be an alkyl, aryl, amino or alkoxy group. The unpaired electron does not reside on one particular atom but rather it extends over all atoms of the S02 group. It should be noted that in recent literature some authors refer to alkanethiyl peroxyl radicals, the adduct of alkanethiyl (RS ) to molecular oxygen, as RS02 rather than RSOO and the fact has already caused some inconvenience. 

Molecular oxygen in the ground state is a diradical with one unpaired electron on... 

Alcohols, like hydrocarbons, are oxidized by the chain mechanism. The composition of the molecular products of oxidation indicates that oxidation involves first the alcohol group and the neighboring C—H bond. This bond is broken more readily than the C—H bond of the corresponding hydrocarbon, since the unpaired electron of the formed hydroxyalkyl radical interacts with the p electrons of the oxygen atom. 

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