Recent low energy electron diffraction experiments have shown that partial dissociation of benzene at the Ir{100} surface yields an ordered overlayer of ortho-benzyne radicals (C6H4) with ring-planes inclined at 47.2degrees to the normal. The primary molecule-surface interaction may be attributed to sigma bonds between radical C and surface Ir atoms, but this characteristic alone does not uniquely constrain the adsorbate to the observed orientation. Through first-principles density functional theory which gives good agreement with the experimental structure, we now demonstrate that the molecular tilt arises due to interaction of the aromatic pi orbitals with the surface d orbitals, and not because of any dispersive intermolecular forces.