Photoelectron Spectra and Electronic Structures of Substituted Pyrimidines

The electronic structures of pyrimidine (1) and its substituted derivatives 2−15 have been investigated by ultraviolet photoelectron spectroscopy and quantum chemical methods. The ionisation potentials corresponding to the π MOs π1‐π3 and the two nN orbitals of the pyrimidine unit could be determined and assigned for 1−15. Multiple linear regression analyses of the IPs related to these orbitals with different substituent constants indicated that Hammett σp values performed well for all these IPs, whereas the resonance parameters R and R+ were satisfactory for π and poor for nN ionisations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)