Biswajit Bandyopadhyay, Tim Cheng and Michael A. Duncan Department of Chemistry, University of Georgia, Athens, GA, Infrared Spectroscopy of Protonated Benzene-Water Complexes

Motivation Proton transfer is ubiquitous in chemistry and biology. Bridged proton systems are key intermediates in proton transfer reactions. Protonated benzene-water complexes provide a simple system to study hydrophobic-hydrophilic interface. Protonated benzene complex and protonated water clusters have been studied by our group previously.

J. R. Roscioli, L. R. McCunn, M. A. Johnson, Science, 2007, 316, 249 PA of water: kJ/mol PA of Benzene: kJ/mol ∆PA( Bz-water ): kJ/mol

Experimental Arc Discharge(1-2kV) to create ions Mass Selection IR Excitation cm cm -1

(Bz)H + (H 2 O)Ar→(Bz)H + (H 2 O)+Ar B3LYP/6-311+G(d, p) Ar B.E.= 2.0 kcal/mol B.E.= 25 kcal/mol B.E.= 26 kcal/mol Infrared spectrum of protonated benzene-water complex

∆E= 0 kcal/mol ∆E= 13.7 kcal/mol B3LYP/6-311+G(d, p) ( Bz)H + (H 2 O) 2 →(Bz)+(H 2 O) 2 H + H + (H 2 O) 2 Ar→H + (H 2 O)+Ar Looks like protonated Water dimer Infrared spectrum of protonated benzene-(water) 2 complex

∆E= 0 kcal/mol ∆E= 20.9 kcal/mol (Bz)H + (H 2 O) 3 →(Bz)+(H 2 O) 3 H + H + (H 2 O) 3 Ar→H + (H 3 O)+Ar Infrared spectrum of protonated benzene-(water) 3 complex Looks like protonated Water trimer

∆E= 24.9 kcal/mol ∆E= 0 kcal/mol (Bz)H + (H 2 O) 4 →(Bz)+(H 2 O) 4 H + H + (H 2 O) 4 Ar→H + (H 4 O)+Ar Infrared spectrum of protonated benzene-(water) 4 complex Looks like protonated Water tetramer

∆E= 6.6 kcal/mol ∆E= 0 kcal/mol (Bz) 2 H + (H 2 O)Ar→ (Bz) 2 H + (H 2 O) + Ar Infrared spectrum of protonated (benzene) 2 -(water) complex

(Bz) 2 H + (H 2 O) 3 → (Bz)H + (H 2 O) 3 + Bz Infrared spectrum of protonated (benzene) 2 -(water) 3 complex

Conclusions Various isomers are possible but the location of the proton is determined by the solvation energy Structures consist primarily of protonated water clusters interacting with neutral benzene. Acknowledgement Michael A. Duncan Gary E. Douberly Allen M. Ricks NSF for funding