Electron density distribution 1,3,5-hexatriene

Figure 1.4 shows electron density contours for benzene and 1,3,5-hexatriene. Note that the contours show completely uniform electron density distribution in benzene, but significant concentration between atoms 1,2 3,4 and 5,6 in hexatriene, as was argued qualitatively above. 

The addition or subtraction of an electron makes the distribution non-uniform (Fig. 4.3d-e). Also in six r-electron hexatriene molecules, uniform electron density is out of the question (Fig. 4.3b). Note that the maxima of the density coincide with the double bonds chemists like to write down. However, even in this molecule, there is still a certain equalization of bonds, since the TT electrons are also where chemists write a single bond (although the tt electron density is smaller over there ). 

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