Cover Picture: A Hydrogen-Bond Flip-Flop through a Bjerrum-Type Defect (Angew. Chem. Int. Ed. 9/2013)



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Hydrogen bonds can dynamically reverse their direction by means of an ultrafast flip-flop motion of the donor and acceptor moieties engaged in the noncovalent contact. In their Communication on page 2602 ff., P. Vöhringer and co-workers describe an application of femtosecond two-dimensional infrared exchange spectroscopy (2DIR-EXSY) in which these elementary dynamics are observed in the time domain of a simple model system, a vicinal diol.