Systematic ab initio study of 15N-15N and 15N-1H spin-spin coupling constants across N-H+-N hydrogen bonds: predicting N-N and N-H coupling constants and relating them to hydrogen bond type.
A systematic ab initio EOM-CCSD study of 15N-15N and 15N-1H spin-spin coupling constants has been carried out for a series of complexes formed from 11 nitrogen bases with experimentally measured proton affinities. When these complexes are arranged in order of increasing proton affinity of the proton-acceptor base and, for each proton acceptor, increasing order of proton affinity of the protonated N-H donor, trends in distances and signs of coupling constants are evident that are indicative of the nature of the hydrogen bond. All two-bond spin-spin coupling constants (2hJ(N-N)) are positive and decrease as the N-N distance increases. All one-bond N-H coupling constants (1J(N-H)) are negative (1K(N-H) are positive). 1J(N-H) is related to the N-H distance and the hybridization of the donor N atom. One-bond H...N coupling constants (1hJ(H-N)) are positive (1hK(H-N) are negative) for traditional hydrogen bonds, but 1hJ(H-N) becomes negative when the hydrogen bond acquires sufficient proton-shared character. The N-N and H...N distances at which 1hJ(H-N) changes sign are approximately 2.71 and 1.62 A, respectively. Predictions are made of the values of 2hJ(N-N) and 1J(N-H), and the signs of 1hJ(H-N), for those complexes that are too large for EOM-CCSD calculations.
Del Bene
Janet E
JE
Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555, USA. jedelbene@ysu.edu
Elguero
José
J
D006859:Hydrogen / Q000737:chemistry*; D006860:Hydrogen Bonding; D008956:Models, Chemical; D009584:Nitrogen / Q000737:chemistry*; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular; D009930:Organic Chemicals / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory
D009587:Nitrogen Isotopes; D009930:Organic Chemicals; D011522:Protons; D006859:Hydrogen; D009584:Nitrogen