Friedel oscillations arise due to the large enough electron delocalization within a considered molecule or quantum system (please see Appendix A.2 for different delocalization measures). The most obvious candidates for such a system are metals; however, strongly conjugated π-electron systems should also be considered. For example, a prediction of charge density waves in conjugated π-electron systems has been introduced as early as 1968 in a paper by E. W. Fenton 142 to explain the bond alteration in long polyenes. In this section, we show how FOs appear in such carbon chains. To illustrate some effects and provide the basis for an in-depth discussion of FOs, we have performed some textbook Hartree-Fock and density functional theory calculations for selected long carbon chains. Details of these calculations can be found in the Appendix A.3. Finally, we make a connection to the mesomeric effect observed in various organic molecules. 7