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Two-Bond ¹⁹F−¹⁵N Spin−Spin Coupling Constants (^2hJ_F-N) across F−H···N Hydrogen Bonds

Janet E. Del Bene,*^†^‡ S. Ajith Perera,^† Rodney J. Bartlett,^† Manuel Yáñez,^§ Otilia Mó,^§ José Elguero, and Ibon Alkorta

Quantum Theory Project, University of Florida, Gainesville, Florida 32611, Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555, Departamento de Química, C-9, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain, and Instituto de Química, Médica, CSIC, Juan de la Cierva, 3, 28006-Madrid, Spain

J. Phys. Chem. A, 2003, 107 (17), pp 3121–3125

DOI: 10.1021/jp022555h

Publication Date (Web): April 5, 2003

In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.

†

University of Florida.

‡

Youngstown State University.

Universidad Autónoma de Madrid.

‖

Instituto de Química, Médica, CSIC.

Abstract

Equation-of-motion coupled cluster calculations (EOM-CCSD) have been performed to determine two-bond ¹⁹F−¹⁵N spin−spin coupling constants (^2hJ_F_-_N) for thirteen neutral complexes stabilized by F−H···N hydrogen bonds. The proton acceptors include nitrogens that are sp (HCN and its derivatives), sp² (aromatic azines), and sp³ (NH₃ and its derivatives) hybridized. ^2hJ_F_-_N is determined by the Fermi-contact term, which is strongly dependent on the intermolecular F−N distance but varies only slightly with small perturbations of the hydrogen bond from linearity. ^2hJ_F_-_N is more sensitive to the hybridization and bonding at the nitrogen in F−H···N hydrogen bonds than is ^2hJ_N_-_N for complexes stabilized by N−H−N and N−H⁺−N hydrogen bonds. As a result, ^2hJ_F_-_N at the same F−N distance for different complexes can vary by 10−15 Hz, and this reduces the quality of the quadratic curve used to relate ^2hJ_F_-_N to the F−N distance. However, if the complexes are grouped according to the hybridization of the nitrogen, excellent quadratic correlations are found between ^2hJ_F_-_N and the F−N distance. Moreover, if the same groupings are used, ^2hJ_F_-_N also correlates with the charge density at the bond critical point of the hydrogen bond.