Monofluorobenzene cation

The spectroscopic technique described above is applicable to most ionic states, but is particularly useful for nonfiuorescing or nonpredissociating molecular ion states, such as those of many radical cations. Because of the considerably lower energies of their first excited electronic states in comparison to their neutral parent molecules, internal conversion is enhanced, thus suppressing fluorescence. Typical examples are the cations of all mono- and of many di- and trihalogenated benzenes as well as of the benzene cation itself. For illustration, the UV/VIS spectrum of the monofluorobenzene cation shown in Fig. 4.41c was measured by the method described above and revealed for the first time vibrational resolution for this molecular cation. 

The importance of electrostatics in the interaction of aromatics fluorine with cations and hydrogen bond donors can be visualized using electrostatic potential surfaces (Figure 20.37). In monofluorobenzene, the potential of the fluorine is concentrated on the unique fluorine present, whereas in polyfluorobenzene the negative charge is spread over several fluorine atoms. For this reason, monofluorobenzene may give stronger interactions. 

Zakharieva, O., M. Grodzicki, A.X. Trautwein, C. Veeger, and I.M.C.M. Rietjens (1996). Molecular orbital study of the hydroxylation of benzene and monofluorobenzene catalysed by iron-oxo porphyrin TT-cation radical complexes. J. Biol. Inorg. Chem. 1, 192-204. 

---

See also in sourсe #XX -- [ , , , ]

---