State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Beijing National Laboratory for Molecular Science (BNLMS), Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080, China.
Aromatic isothiocyanates are interesting pseudohalides molecules which are widely existed in healthy intact
plants. However, few attempts were made to analyze their structures and correlate their electronic structure with other properties (e.g., chemical reactivity). In this paper, the electronic structures and substituent effects of o-, m-, and piodophenyl isothiocyanates were studied by the ultraviolet photoelectron spectroscopy and discussed through the careful analysis of ionization potentials corresponding to π and n orbitals. Owing to the effects of the iodine atom and the NCS group, the first ionization potentials of iodophenyl isothiocyanates are lower than that of iodobenzene and phenyl isothiocyanate. And the energetic order of the first six MOs is π3 > π2 > nS > n॥ > πNCS > n┴. The energy and electron density of the topmost occupied molecular orbitals of iodophenyl isothiocyanates were analyzed. It has been found that the ionization energy of πNCS orbital electrons in ρ -iodophenyl isothiocyanate is the lowest of the three iodophenyl isothiocyanates, which indicates the chemical reactivity of ρ -iodophenyl isothiocyanate is the highest.