The group derived by loss of an H from benzene is a phenyl
group abbreviated Ph.
The phenyl radical (C6H5·) is
the prototypical σ-type aryl radical and one of
the most common aromatic building
blocks for larger ring
molecules. Using a
combination of rotational spectroscopy of singly substituted isotopic species and vibrational corrections
calculated theoretically, an extremely accurate molecular structure has been determined.
Figure
1. Side-by-side comparison of the
structures of benzene
and the phenyl radical.
The phenyl radical (C6H5·) is a highly reactive
species formed by the homolytic
cleavage of a C–H
bond in benzene (Figure 1), the prototypical
aromatic compound. It is one of the most common aromatic radicals, and plays a central role in many reactions, ranging from astronomy to
combustion and biochemistry.
As the simplest aryl radical, it also serves as the benchmark for
computational investigations of larger, open-shell ring molecules.
The reactivity of aryl radicals is due to the localization of the unpaired electron in a σ-type orbital at the C–H cleavage site, as
indicated by the
very high C–H bond dissociation
energy of benzene (465 ± 3 kJ mol-1).
