Substitution and protonation effects on spin-spin coupling constants in prototypical aromatic rings: C6H6, C5H5N and C5H5P.
Ab initio equation-of-motion coupled cluster calculations have been carried out to evaluate one-, two-, and three-bond 13C-13C, 15N-13C, 31P-13C coupling constants in benzene, pyridine, pyridinium, phosphinine, and phosphininium. The introduction of N or P heteroatoms into the aromatic ring not only changes the magnitudes of the corresponding X-C coupling constants (J, for X = C, N, or P) but also the signs and magnitudes of corresponding reduced coupling constants (K). Protonation of the heteroatoms also produces dramatic changes in coupling constants and, by removing the lone pair of electrons from the sigma-electron framework, leads to the same signs for corresponding reduced coupling constants for benzene, pyridinium, and phosphininium. C-C coupling constants are rather insensitive to the presence of the heteroatoms and protonation. All terms that contribute to the total coupling constant (except for the diamagnetic spin-orbit (DSO) term) must be computed if good agreement with experimental data is to be obtained.
Del Bene
Janet E
JE
Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555, USA. jedelbene@ysu.edu
Elguero
José
J
D001554:Benzene / Q000737:chemistry*; D001555:Benzene Derivatives / Q000737:chemistry*; D007554:Isotopes / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009943:Organophosphorus Compounds / Q000737:chemistry*; D011522:Protons; D011725:Pyridines / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000737:chemistry
D001555:Benzene Derivatives; D007554:Isotopes; D009943:Organophosphorus Compounds; D011522:Protons; D011725:Pyridines; D011726:Pyridinium Compounds; C519090:phosphinine; D001554:Benzene; C023666:pyridine