Analysis of long-range NMR spin-spin coupling in polyenes and the π-mechanism

Jürgen Gräfenstein, Tell Tuttle, Dieter Cremer

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

The J-OC-PSP (decomposition of J into Orbital Contributions using Orbital Currents and Partial Spin Polarization) method is applied to analyze NMR spin-spin coupling constants in polyenes, which were calculated using coupled perturbed density functional theory in connection with the B3LYP hybrid functional and a [7s,6p,2d/4s,2p] basis set. The analysis revealed that the π-mechanism for Fermi contact (FC) spin coupling is based on passive π-orbital contributions. The π-orbitals transfer spin information between σ orbitals (spin-transport mechanism) or increase the spin information of a σ orbital by an echo effect. The calculated FC(π) values are rather constant for small polyenes ranging between 3.5-5.5 Hz for a double bond. They decay more slowly with the distance between perturbing and responding nucleus than the σ contributions to the FC term. The sign of the passive FC(π) contribution can be assessed from a Dirac vector model. The limits for longrange coupling in a polyene were determined and their practical implications discussed.

Original languageEnglish
Pages (from-to)452-462
Number of pages11
JournalPhysical Chemistry Chemical Physics
Volume7
Issue number3
Early online date12 Jan 2005
DOIs
Publication statusPublished - 7 Feb 2005

Keywords

  • decomposition
  • spin-spin coupling constants
  • SSCCs
  • Fermi contact spin coupling

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