Oxygen paramagnetism, illustration

Figure 7.4 Schematic of 180° superexchange between two paramagnetic cations via the filled p orbitals of an intermediate oxygen ion, illustrated by Mn ...

A cyclization reaction involving a half-formed bridge in which alkyl halide functions interact with (initially) coordinated oxygen atoms is illustrated by [2.9] (Kluiber Sasso, 1970). The X-ray structure of the red paramagnetic nickel complex (65) indicates that the macrocycle coordi-... 

An important illustration of the importance of the Pauli exclusion principle is seen in the Oj molecule. If we were to describe Oj using either the sp hybridization or bent bond model, we would expect a double bond with all the electrons paired. In fact, O2 is paramagnetic, with two unpaired electrons, and yet it does have a double bond. If we ask how electrons would be distributed to maintain maximum separation, we arrive at two tetrahedral arrays, with the tetrahedra offset by the maximum amount. Electronic spin can be represented as x and 0. The structure still has four bonding electrons between the oxygen atoms, that is, a double bond. It also obeys the octet rule for each oxygen and correctly predicts that two of the electrons are unpaired. 

The blue question mark suggests that there is some doubt about the validity of structure (10.9), and the source of the doubt is illustrated in Figure 10-3. The structure fails to account for the paramagnetism of oxygen—the O2 molecule must have unpaired electrons. Unfortunately, no completely satisfactory Lewis structure is possible for O2, but in Chapter 11, bonding in the O2 molecule is described in a way that accounts for both the double bond and the observed paramagnetism. 

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