Ab Initio EOM-CCSD Spin-Spin Coupling Constants for Hydrogen-Bonded Formamide Complexes: Bridging Complexes with NH3, (NH3)2, H2O, (H2O)2, FH, and (FH)2
EOM-CCSD spin−spin coupling constants across hydrogen bonds have been computed for complexes in which NH3, H2O, and FH molecules and their hydrogen-bonded dimers form bridging complexes in the amide region of formamide. The formamide one-bond N−H coupling constant [1J(N−H)] across N−H···X hydrogen bonds increases in absolute value upon complexation. The signs of the one-bond coupling constants 1hJ(H−X) indicate that these complexes are stabilized by traditional hydrogen bonds. The two-bond coupling constants for hydrogen bonds with N−H as the donor [2hJ(N−X)] and the carbonyl oxygen as the acceptor [2hJ(X−O)] increase in absolute value in the formamide/dimer relative to the corresponding formamide/monomer complex as the hydrogen bonds acquire increased proton-shared character. The largest changes in coupling constants are found for complexes of formamide with FH and (FH)2, suggesting that bridging FH monomers and dimers in particular could be useful NMR spectroscopic probes of amide hydrogen bonding.