Radical Cation of N,N-Dimethylpiperazine: Dramatic Structural Effects of Orbital Interactions through Bonds

The radical cation of N,N-dimethylpiperazine (DMP) has been studied using time-resolved optical absorption and resonance Raman spectroscopy. Different quantum-chemical methods were used to calculate the molecular structures and vibrational force fields in the ground state of the radical cation and in the resonant excited state. An excellent agreement between theoretical and experimental vibrational frequencies as well as resonance Raman intensities could be achieved. It is concluded that through-σ-bond interaction between the formal lone pair on one amino nitrogen and the odd electron on the other is strong enough to lead to a symmetric charge-delocalized molecular structure of the DMP radical cation, with a chair-type geometry.