1. Infrared Spectroscopy of Protonated Acetylacetone and Mixed Acetylacetone/Water Clusters Daniel T. Mauney, David C. McDonald II, Jonathon A. Maner and Michael A. Duncan Department of Chemistry, University of Georgia, Athens, GA. USA http://research.franklin.uga.edu/maduncan

2. Proton transfer is ubiquitous in chemistry and biology Photosynthesis Electrochemistry Chemical Ionization Mass Spec Astrochemistry Organic Reactions Protonated species are thought to be intermediates http://www.noble.org/plantbio/sumner/ionization-technique/ DeCoursey, Physiol. Rev., 2003, 83, 475

3. Protonation Sites Protons typically prefer to attach to functional groups with electronegative elements Carbonyls Amines Alcohols Our lab has studied a number of protonated carbonyls H + (CO) n * H + (CO 2 ) n 1 H + (Formaldehyde) 2 H + (Biacetyl)* H + (Acetone) n 3 * unpublished 1. Duncan and co., J. Phys. Chem. A., 2008, 112, 950-959 2. Duncan and co., J. Phys. Chem. A., 2012, 116, 9287 3. Duncan and co.., Phys. Chem. Chem. Phys., 2008, 10, 77-79

4. Proton-Bound Dimers Protonated species and their dimers have been source of extensive research 4-9 Shared proton stretch frequency depends on difference in proton affinity of species This stretch can broaden and split depending on coupling between shared proton and backbone motions Harmonic frequency calculations have problems getting the positions and relative intensities of bands correct Duncan and co., Phys. Chem. Chem. Phys., 2008, 10, 77-79 4. Lee et al., J. Chem. Phys., 1989, 91, 7319 5. Asmis et al., Science, 2003, 299, 1375 6. Moore et al., ChemPhysChem, 2004, 5,740 7. Headrick et al., Science, 2005, 308, 1765 8. Hammer et al., J. Chem. Phys., 2005, 122, 244301 9. Fridgen et al., Phys. Chem. Chem. Phys., 2006, 8, 955 10. Johnson and co., Science, 2007, 316,249 Johnson and co., Science, 2007, 316,249

5. Intramolecular Proton-Bound Dimers Studied previously by Johnson and coworkers using vibrational spectroscopy previously in substituted naphthalene complexes 11 Acetylacetone (AcAc) is the simplest of the beta-diketones Two Tautomers Equilibrium Shifts based on environment Enol favored in gas phase di-keto favored in polar solvents (like water) Enoldi-keto 11. DeBlase et al., J. Chem. Phys., 2013, 139, 024301

6. Mass Selected IR photodissociation (IR-PD) In a Reflectron Time-of-Flight Mass Spectrometer Production of cold ionic and neutral molecules with electrical discharge in a supersonic expansion. IR photodissociation spectroscopy via argon tagging.

7. H + (AcAc)-Ar E10.0 kcal/molE2+2.5 K1+5.8 E3+11.7 Structures and their relative energies computed at the B3LYP/6-311+G** level of theory Note: There are two other di-Keto isomers, but their energy is significantly higher than the other isomers

8. H + (AcAc)-Ar Peak relative intensities consistent with lowest energy enol isomer Without scanning lower than 2000 cm -1, lowest keto isomer can not be excluded

9. H + (AcAc) 2 We have yet to find an isomer that explains each of the peaks in the current spectrum.

10. Monomer vs Water Complex Water complex previously studied by Chang 12 We are trying to expand on that work Multiple new peaks in the OH stretching region 12. Chang and coworkers, Mol. Phys., 2003, 101, 1285

11. H + (AcAc)(H 2 O)-Ar Spectrum obtained is believed to be from a mixture of the two lowest energy isomers

12. Conclusions We are currently probing structures of protonated acetylacetone monomer and dimer as well as the monomer/water complex. The protonated monomer spectrum is consistent with the lowest energy enol isomer, but may still contain the keto isomer (+5.8 kcal/mol). No isomer has yet been found for the dimer that would be consistent with the spectrum. The water complex spectrum is believed to be from a mixture of the two lowest energy isomers, but further study is needed to confirm this hypothesis

13. Acknowledgements Dr. Michael Duncan The Duncan Research Group The University of Georgia National Science Foundation