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Two-Bond ¹³C−¹⁵N Spin−Spin Coupling Constants (^2hJ_C_-_N) Across C−H−N Hydrogen Bonds^†

Janet E. Del Bene,*^‡^§ S. Ajith Perera,^‡ Rodney J. Bartlett,^‡ Manuel Yañez, 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 (18), pp 3222–3227

DOI: 10.1021/jp021619l

Publication Date (Web): November 12, 2002

†

Part of the special issue “George S. Hammond & Michael Kasha Festschrift.”

Corresponding author. E-mail: fr042008@ysub.ysu.edu.

‡

University of Florida.

Youngstown State University.

‖

Universidad Autónoma de Madrid.

⊥

CSIC.

Abstract

Ab initio EOM-CCSD calculations have been performed to determine ¹³C−¹⁵N spin−spin coupling constants (^2hJ_C_-_N) across C−H−N hydrogen bonds in 17 neutral, 3 cationic, and 3 anionic complexes. The contributions of the paramagnetic spin−orbit, diamagnetic spin−orbit, and spin−dipole terms to the total ¹³C−¹⁵N spin−spin coupling constants (^2hJ_C_-_N) are negligible, so ^2hJ_C_-_N is determined solely by the Fermi contact term, which is distance-dependent. ^2hJ_C_-_N for complexes stabilized by C−H···N hydrogen bonds exhibits some dependence on the nature of the hybridization and the nature of the bonding at the C atom of the proton-donor C−H group. Nevertheless, a single curve can be constructed from ^2hJ_C_-_N and C−N distances for the equilibrium structures of the entire set of complexes that should be useful for estimating C−N distances from experimental measurements of coupling constants across C−H−N hydrogen bonds. Small deviations from linearity of the C−H−N hydrogen bond lead to only small changes in ^2hJ_C_-_N.