Gas phase vibrations of an anionic, hydrogen-bonded homodimer of a nucleobase analogue: Isocytosino-8-trifluoromethylquinolone

Synthesis and spectra of isocytosino-8-trifluoromethylquinolone (1), as well as the gas phase InfraRed Multiple Photon Dissociation (IRMPD) spectra in the fingerprint region of the corresponding deprotonated anion (3), its d₃ analogue, the monodeprotonated homodimer (2), and its d₇ analogue are reported here. The anions represent nucleobase analogues having the hydrogen bonding pattern ADAAD (where A stands for acceptor and D stands for donor), in which the site of negative charge is unambiguous (as opposed to guanine, which has more than one acidic nitrogen). The match between experimental vibrational spectra and calculation is good, except for the out-of-plane HNH bends of the undeuterated and deuterated monomer anions between 400 and 600 cm⁻¹. The anionic homodimers form in a parallel orientation.