Yang and Heilbronner used a Hückel model to predict how bond localization is alleviated by electron-donating substituents at positions with large LUMO coefficients or by electronwithdrawing substituents at HOMO coefficient positions. We apply this strategy using donor substituents at LUMO positions (step 3 in Figure ). Yang and Heilbronner noted that electron-withdrawing substituents seem to have less effect in practice. Our results agree with this, and we find primarily that electron-donating substituents at the LUMO positions have a notable effect on the bond-length alternation of the molecular core.