Opening of the Diamondoid Cage upon Ionization Probed by Infrared Spectra of the Amantadine Cation Solvated by Ar, N2, and H2O

Chemistry. 2022 May 25. doi: 10.1002/chem.202200577. Online ahead of print.ABSTRACTRadical cations of diamondoids, a fundamental class of very stable cyclic hydrocarbon molecules, play an important role in their functionalization reactions and the chemistry of the interstellar medium. Herein, we characterize the structure, energy, and intermolecular interaction of clusters of the amantadine radical cation (Ama + , 1-aminoadamantane) with solvent molecules of different interaction strength by infrared photodissociation (IRPD) spectroscopy of mass-selected Ama + L n clusters, with L=Ar ( n ≤3) and L=N 2 and H 2 O ( n =1), and dispersion-corrected density functional theory calculations (B3LYP-D3/cc-pVTZ). Three isomers of Ama + generated by electron ionization are identified by the vibrational properties of their rather different NH 2 groups. The ligands bind preferentially to the acidic NH 2 protons, and the strength of the NH…L ionic H-bonds are probed by the solvation-induced red-shifts in the NH stretch modes. The three Ama + isomers include the most abundant canonical cage isomer ( I ) produced by vertical ionization, which is separated by appreciable barriers from two bicyclic distonic iminium ions obtained from cage-opening (primary radical II ) and subsequent 1,2 H-shift (tertiary radical III ), the latter of which is the global minimum on the Ama + potential energy surface. The effect of solvation on the energetics of the reaction potential revealed by the calculati...
Source: Chemistry - Category: Chemistry Authors: Source Type: research