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Angular dependence of geminal spin–spin coupling constants in a prototype CH 2 group. J (H,H) versus interbond angle in methane
Author(s) -
Geertsen Jan,
Oddershede Jens,
Raynes William T.
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310806
Subject(s) - geminal , chemistry , coupling constant , spin (aerodynamics) , proton , atomic physics , coupling (piping) , ab initio , methane , physics , thermodynamics , stereochemistry , quantum mechanics , mechanical engineering , organic chemistry , engineering
Correlated ab initio calculations of the dependences of the proton–proton spin–spin coupling constant J (H 1 , H 2 ) in methane with the variation of the H 1 CH 2 interbond angle are reported. The other coupling constants, including J (C, H), were simultaneously calculated. The coupling constants J (H 1 , H 2 ) and J (C, H 1 ) increase nearly linearly with the opening of the interbond angle whereas J (H 2 , H 3 ) and J (C, H 3 ) decrease. J (H 3 , H 4 ) is only very slightly affected. The changes are due almost solely to changes in the Fermi contact term. The angular dependence is slightly larger at the SCF level of calculation than at the correlated level. The change in the geminal coupling constant J (H 1 , H 2 ) with respect to equilibrium geometry is given to within 0.025 Hz by Δ J (H 1 , H 2 ) (Hz) = 41.57 sin α 12 − 8.90 sin 2 α 12 , where α 12 is the increase in the interbond angle with respect to equilibrium ( − 10° ⩽ α 12 ⩽ 10°).