Photodetachment of Deprotonated R-Mandelic Acid: The Role of Proton Delocalization on the Radical Stability

The photodetachment and stability of R-Mandelate, the deprotonated form of the R-Mandelic acid, was investigated by observing the neutral species issued from either simple photodetachment or dissociative photodetachment in a cold anions set-up. R-Mandalate has the possibility to form an intramolecular ionic hydrogen-bond between adjacent hydroxyl and carboxylate groups. The potential energy surface along the proton transfer (PT) coordinate between both groups (O- horizontal ellipsis H+ horizontal ellipsis -OCO) features a single local minima, with the proton localized on the O- group (OH horizontal ellipsis -OCO). However, the structure with the proton localized on the -OCO group (O- horizontal ellipsis HOCO) is also observed because it falls within the extremity of the vibrational wavefunction of the OH horizontal ellipsis -OCO isomer along the PT coordinate. The stability of the corresponding radicals, produced upon photodetachment, is strongly dependent on the position of the proton in the anion: the radicals produced from the OH horizontal ellipsis -OCO isomer decarboxylate without barrier, while the radicals produced from the O- horizontal ellipsis HOCO isomer are stable.

Automated summary

The photodetachment and stability of R-Mandelate, the deprotonated form of R-Mandelic acid, were investigated. It was found that R-Mandelate has the possibility to form an intramolecular ionic hydrogen-bond, and the stability of the resulting radicals is dependent on the position of the proton.