Reversal in the sequence of the two highest occupied molecular orbitals in the series pyrazine, 2,6-dimethylpyrazine, and tetramethylpyrazine

Abstract

Comparison between the photoelectron spectra of pyrazine (1), 2,6-dimethylpyrazine (2), and tetramethylpyrazine (3) indicates that in (3) the HOMO is π(b2g) while in (1) and (2) it is n+, suggesting a different behaviour towards electrophilic attack on (3) compared with (1) and (2).