Atomic orbitals model and

Figure 2. [TCNE] [Bu,N].+ spin density obtained by MaxEnt reconstruction using an atomic orbital model, and subsequent projection onto the molecular plane of [TONE]-. Positive contour steps are 50 mpE/A- and negative contours are dashed (step 10mpB/A2). A significant off-centring is present.

The simple MO and VB treatments of benzene begin with the same atomic-orbital model and each treats benzene as a six-electron 77-bonding problem. The assumption is that the a bonds of benzene should not be very much different from those of ethene and may be regarded as independent of the 77 system. 

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