An Accurate Molecular Structure of Phenyl, the Simplest Aryl Radical

The phenyl radical (C6H5.) is the prototypical sigma-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. Relative to benzene, the phenyl radical has a substantially larger C-C-ipso-C bond angle [125.8(3)degrees vs. 120 degrees], and a shorter distance [2.713(3)angstrom vs. 2.783(2)angstrom] between the ipso and para carbon atoms.