To better understand the nature of the orbital contributions, we compute the phase and transmission through individual MOs. For benzene, the phases are presented in Figure and the MO contributions to the transmission (|t i | 2 ) are presented in Figure . We can understand the differences between meta and para substitution by considering the differences in the transmission and phase of three pairs of orbitals: the HOMO and LUMO, the HOMO ′ and LUMO ′ , and the HOMO-1 and LUMO+1. For each case, these pairs of orbitals are symmetry related (from the Coulson-Rushbrooke orbital pairing theorem ). This results in equal widths for the transmission peaks from paired orbitals as well as identical lineshapes for the phase as a function of energy (shifted in energy).