Substituent effect on electronic structures of halonitrobenzenes.

The electronic structures and substituent effects of o-, m-, and p-chloronitrobenzene and bromonitrobenzene have been studied by ultraviolet photoelectron spectroscopy (UPS). It was found that the o-isomer possesses particular electronic properties. This characteristic depends on the conjugation between the benzene ring pi orbital and the nitro group pi orbital and the interaction of the halogen and nitro groups in the adjacent position.