Resolving an apparent discrepancy between theory and experiment: spin-spin coupling constants for FCCF.
Janet E Del Bene1, Patricio F Provasi, Ibon Alkorta
1Department of Chemistry, Youngstown State University, Youngstown, Ohio 44555, USA. jedelbene@ysu.edu
Magnetic Resonance in Chemistry : MRC
|September 16, 2008
Summary
Ab initio calculations for difluoroethyne (FCCF) resolve a long-standing theory-experiment discrepancy for the spin-spin coupling constant (3)J(F-F). This study provides accurate theoretical values for FCCF coupling constants, aiding future research.
Area of Science:
- Quantum chemistry
- Computational physics
- Spectroscopy
Background:
- Spin-spin coupling constants provide insights into molecular structure and electronic properties.
- Previous theoretical studies on difluoroethyne (FCCF) showed discrepancies with experimental values for the (3)J(F-F) coupling constant.
Purpose of the Study:
- To accurately compute spin-spin coupling constants for FCCF using advanced theoretical methods.
- To resolve the discrepancy between theoretical and experimental values for (3)J(F-F) in FCCF.
- To investigate the factors influencing the (3)J(F-F) coupling constant.
Main Methods:
- Ab initio equation of motion coupled cluster singles and doubles (EOM-CCSD) calculations.
- Second-order polarization propagator approximation (SOPPA) calculations.
- Evaluation of spin-spin coupling constants, including (3)J(F-F), (1)J(C-C), (1)J(C-F), and (2)J(C-F).
Main Results:
- The computed EOM-CCSD value for (3)J(F-F) at the experimental geometry agrees with the experimental value of 2.1 Hz, resolving the discrepancy.
- The (3)J(F-F) coupling constant is sensitive to C-C and C-F bond distances and depends on paramagnetic spin-orbit (PSO) and spin-dipole (SD) contributions.
- Calculated (1)J(C-F) agrees with experimental data, while (2)J(C-F) is computed to be larger than the estimated experimental value.
Conclusions:
- The study successfully resolves the theoretical-experimental discrepancy for (3)J(F-F) in FCCF using EOM-CCSD.
- The findings highlight the importance of accurate theoretical methods and the balance of PSO and SD terms in determining spin-spin couplings.
- Further investigation may be needed for the (2)J(C-F) coupling constant to reconcile computed and experimental values.
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