Vibrational contributions to vicinal proton-proton coupling constants3JHH

• Published in: Molecular physics Vol. 108; no. 5; pp. 583 - 595
• Main Authors: Esteban, Angel L, Diez, Ernesto, Galache, Maria P, San Fabian, Jesus, Casanueva, Jorge, Contreras, Ruben H
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Ltd 01-02-2010
• Subjects: Computation; Coupling (molecular); Couplings; Derivatives; Deviation; Mathematical models; Molecular physics; Standard deviation
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268971003630687

Vibrational contributions to the [image omitted] couplings of six mono- and five 1,1-di-substituted ethanes, three mono-substituted cyclohexanes, three norbornane-type molecules, and 11 three-membered rings have been calculated at the DFT/B3LYP level for the Fermi contact term using a moderate sized basis set. When, for a data set of 70 couplings, the sums of the values for the equilibrium configurations Je and the respective vibrational contributions [image omitted] at 300 K are multiplied by a factor of 0.8485, the corresponding predicted couplings [image omitted] are in good agreement with the experimental couplings [image omitted] with a standard deviation σ of 0.18 Hz. The same σ results when [image omitted] values are obtained by multiplying the Je values by 0.9016. However, the vibrational contributions must be taken into account, together with the Je values, in order to achieve a procedure for a reliable and accurate prediction of [image omitted] couplings since, globally, [image omitted] contributions amount to about 7% of the Je values and the correlation coefficient between [image omitted] and Je is only 0.68 with a σ deviation of 0.20. The first and diagonal second derivatives of J with respect to each normal coordinate Qk, required to estimate the vibrational contributions, have been obtained from six Jk values computed for molecular geometries positively [image omitted] and negatively [image omitted] displaced from the equilibrium geometry along the normal coordinate Qk and using for δ the values 0.01, 0.05 and 0.10. The computational precision of the results obtained when using one, two and three δ values is analysed.