NMR shielding constants in group 15 trifluorides.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Nuclear Magnetic Resonance Spectroscopy

Background:

• Nuclear magnetic resonance (NMR) shielding constants are crucial for molecular structure determination.
• Accurate prediction of NMR parameters, especially for compounds with significant dynamic electron correlation, remains a challenge.
• Group 15 trifluorides (NF3, PF3, AsF3) serve as excellent test cases due to their electronic properties.

Purpose of the Study:

• To achieve near-quantitative accuracy in calculating NMR shielding constants for NF3, PF3, and AsF3.
• To investigate the impact of dynamic electron correlation on NMR shielding constants.
• To validate advanced theoretical methods for NMR prediction and guide experimental efforts.

Main Methods:

• Coupled-cluster theory calculations, including up to CCSDT expansions.
• Extensive basis sets, such as aug-cc-pCV6Z, and complete basis set (CBS) extrapolations.
• Inclusion of rovibrational and relativistic corrections to computed geometries and energies.

Main Results:

• Near-quantitative accuracy for NMR shielding constants in NF3, PF3, and AsF3 was demonstrated.
• The study highlights the importance of large basis sets and high-level coupled-cluster expansions.
• A revised reference 19F NMR shielding constant for gas-phase CFCl3 was determined by combining chemical shifts.

Conclusions:

• State-of-the-art theoretical techniques can accurately predict NMR shielding constants.
• These computational methods can effectively guide and supplement NMR experimentation.
• The findings provide a robust benchmark for future theoretical studies on NMR properties.