H/D Isotope Effects in Hydrogen Bonded Systems

Molecules

Lucjan Sobczyk¹  Monika Obrzud² 

[1] Faculty of Chemistry, University of Wrocław, Joliot-Curie 14, 50-383 Wrocław, Poland;

关键词: hydrogen bonding;    isotope effects;    infrared spectra;    NQR and NMR spectra;    ferroelectric properties;   

DOI  :  10.3390/molecules18044467

来源: mdpi

【 摘 要 】

An extremely strong H/D isotope effect observed in hydrogen bonded A-H^…B systems is connected with a reach diversity of the potential shape for the proton/deuteron motion. It is connected with the anharmonicity of the proton/deuteron vibrations and of the tunneling effect, particularly in cases of short bridges with low barrier for protonic and deuteronic jumping. Six extreme shapes of the proton motion are presented starting from the state without possibility of the proton transfer up to the state with a full ionization. The manifestations of the H/D isotope effect are best reflected in the infra-red absorption spectra. A most characteristic is the run of the relationship between the isotopic ratio ν_H/ν_D and position of the absorption band shown by using the example of NHN hydrogen bonds. One can distinguish a critical range of correlation when the isotopic ratio reaches the value of ca. 1 and then increases up to unusual values higher than . The critical range of the isotope effect is also visible in NQR and NMR spectra. In the critical region one observes a stepwise change of the NQR frequency reaching 1.1 MHz. In the case of NMR, the maximal isotope effect is reflected on the curve presenting the dependence of Δδ (¹H,²H) on δ (¹H). This effect corresponds to the range of maximum on the correlation curve between δH and ΔpK_a that is observed in various systems. There is a lack in the literature of quantitative information about the influence of isotopic substitution on the dielectric properties of hydrogen bond except the isotope effect on the ferroelectric phase transition in some hydrogen bonded crystals.

【 授权许可】

CC BY   
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