Electronic Mechanisms of Intra and Intermolecular J Couplings in Systems with C-H···O Interactions

Abstract

Abstract: Correlation effects on the change of 1J(CH) couplings in model systems I:NCH...H2O and II:CH4...H2O as a function of the H...O distance are discussed. RPA and SOPPA results follow a similar trend in system II. In system I RPA values decrease monotonously as the H...O distance decreases, while SOPPA ones exhibit flat maximum near equilibrium. Such different behavior is ascribed to the π-transmitted component. Intermolecular couplings at the equilibrium geometry of I are analyzed by means of the CLOPPA approach. The larger absolute value of 2hJ(CO) compared to 1hJ(HO) is found to arise from contributions involving a vacant LMO localized in the C-H...O moiety.

Keywords

• C-H...O interactions
• NMR couplings
• Correlation effects
• Intermolecular couplings
• Localized molecular orbitals