Unexpected IR Characteristics of Hydrogen Bonds in the 18-Crown-6-Ether Complex of the H<sub>3</sub>O<sup>+</sup> Hydronium Ion. Can the Location of the Protons Be Specified?
Аннотация
The νas(COC) IR spectral signatures of polyethers in H-bonded hydronium ion complexes have been established in studies of H3O+ and H5O2+ complexes with 15-crown-5, 18-crown-6, dibenzo-18-crown-6, and their open chain poly(ethylene glycol) analogues in 1,2-dichoroethane solutions. When experiment meets theory in the structure of the H3O+·18-crown-6 complex, there is disagreement. While DFT calculations at the BLYP/II‘//BLYP/6-31G* level indicate a C3v structure with three normal, static linear H bonds to alternate O atoms of the crown ether, IR spectroscopy in the ν(C−O−C) region indicates that all six O atoms are equivalent. A new type of low-barrier H-bonding involving rotational mobility of H3O+ is proposed to rationalize the experimental observations.
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