## Abstract

Vicinal coupling constants ^{3}J_{HH} have been calculated at the optimized geometries for a series of selected molecules with the aim of developing a practical procedure for predicting this kind of coupling. Calculations of couplings and optimizations of molecular geometries have been carried out at the DFT/B3LYP level using a moderate sized basis set. When the Fermi contact contributions to ^{3}J_{HH} calculated for 25 mono- and 23 1,1-di-substituted ethanes are multiplied by a factor of 0.904, the corresponding predicted couplings J^{pre} are in good agreement with the experimental J^{exp} couplings, with standard deviation σ of 0.10 Hz. When such a comparison is carried out for the remaining sets of molecules the σ deviation increases to 0.26 Hz for a dataset of 21 couplings from 11 monosubstituted cyclohexanes, to 0.19 Hz for a dataset of 40 couplings from 6 norbornane type molecules and to 0.25 Hz for a dataset of 54 couplings from 14 three-membered rings. For the complete dataset of 163 couplings the σ deviation amounts to 0.20 Hz. This figure is further reduced to 0.17 Hz by adding to the J^{pre} coupling a small correction given by the term -0.15cosφ, depending on the dihedral angle φ between the coupled protons. A larger σ deviation of 0.31 Hz was reported for the best empirically parameterized extended Karplus equation. DFT J^{pre} values could be further improved by more accurate calculations for the pertinent substituted ethane constituents of the molecule in question by applying a substituent effect model.

Original language | English |
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Pages (from-to) | 1307-1326 |

Number of pages | 20 |

Journal | Molecular Physics |

Volume | 103 |

Issue number | 9 |

DOIs | |

State | Published - May 10 2005 |

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