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Dielectric permittivity and temperature effects on spin–spin couplings studied on acetonitrile
Author(s) -
Sahakyan Aleksandr B.,
Shahkhatuni Astghik A.,
Shahkhatuni Aleksan G.,
Panosyan Henry A.
Publication year - 2008
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.2137
Subject(s) - chemistry , dielectric , permittivity , acetonitrile , coupling constant , dipole , scalar (mathematics) , density functional theory , condensed matter physics , relative permittivity , spin (aerodynamics) , coupling (piping) , polarization (electrochemistry) , solvent effects , solvent , thermodynamics , computational chemistry , molecular physics , quantum mechanics , physics , organic chemistry , materials science , geometry , metallurgy , mathematics
Dielectric permittivity (ε) and temperature effects on indirect spin–spin coupling constants were studied using acetonitrile as a probe molecule. Experiments were accompanied by hybrid DFT (density functional theory) studies, where the solvent was modeled using the polarization continuum model. Owing to its numerous types of J ‐couplings, acetonitrile is a very convenient molecule against which various basis sets can be tested or the best basis set can be selected for a given study. The results show reasonable agreement between calculated and experimental values. According to our data, scalar spin–spin coupling constants undergo substantial shifts at lower values of the dielectric constant. Thus J ‐coupling values are not transferable between measurements made at differing ε–conditions, and the assumption of the ε‐independence of the J ‐coupling can lead to crucial mistakes in experiments using low‐ε media. Dielectric permittivity also causes small geometric fluctuations within the molecule, which themselves can affect J ‐coupling values. Examinations of the results computed with frozen and relaxed geometries show that geometry mediation mostly affects the spin‐dipole term of the J ‐coupling; hence, for accurate evaluation of the latter, frozen geometries are not acceptable. Another interesting fact revealed is the connection between the solvent dielectric properties and the temperature‐dependence slopes of J ‐couplings in corresponding media. Copyright © 2008 John Wiley & Sons, Ltd.