NMR Properties of the Formic Acid Dimer

摘要

NMR properties -nuclear quadrupole coupling constants,shielding constants and indirect spin-spin coupling constants -in the formic acid dimer are studied using ab initio methods.The accuracy of the calculations is examined for the C_(2h),minimum structure of (HCOOH)_2,comparing the MCSCF (multi-configuration SCF)and CCSD (coupled cluster singles and doubles)results.The dependence of the NMR parameters on dimer geometry is analysed for simultaneous double proton transfer,considering the C_(2h)minimum,the D_(2h)transition state and a few intermediate structures,as well as for two structures representing single proton transfer.For the nuclei involved in the hydrogen bonds not only the effects of the dimerization are very large;the computed NMR parameters also vary significantly with the structure of the cyclic formic acid dimer.