IR Spectroscopic Properties of H(MeOH)n+ Clusters in the Liquid Phase: Evidence for a Proton Wire

• Published in: Chemistry : a European journal 2008-04, Vol.14 (12), p.3596-3604
• Main Authors: Stoyanov, Evgenii S., Stoyanova, Irina V., Reed, Christopher A.
• Format: Article
• Language: English
• Subjects: Grotthuss mechanism; Hydrogen Bonding; hydrogen bonds; IR spectroscopy; Methanol - chemistry; proton solvate; proton wire; Protons; Solvents - chemistry; Spectrophotometry, Infrared - methods
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.200701746

The long‐standing problem of understanding the nature of the “excess proton” in acidified water is simplified by studying the proton in methanol. The 3D network of hydrogen bonds in H(aq)+ is reduced to a 1D problem. Infrared spectroscopic characterization of linear chain methanol proton solvates in H(CH3OH)n+ for n=2–8 provides insight into some of the puzzling IR spectral features associated with O‐H‐O vibrations. These include the virtual disappearance of otherwise strong bands from H‐bonded methanol molecules adjacent to symmetrical O‐H+‐O groups. The data indicate that a chain of up to four OH⋅⋅⋅O bonds either side of this group can act as an electrical wire to separate positive charge. This suggests a refinement of the Grotthuss proton‐hopping mechanism for explaining the anomalously high mobility of H+ in H‐bonded media. Grotthuss proton‐hopping in methanol is facilitated by the formation of true proton wires up to eight molecules in length (see scheme). This is deduced from condensed phase IR studies of H(CH3OH)n+ clusters (n=2–8).