Counterintuitive deshielding on the C-13 NMR chemical shift for the trifluoromethyl anion

Author(s)

Viesser, Renan V. ; Tormena, Claudio F.

• Document type: Journal article
• Source: Magnetic Resonance in Chemistry; v. 58, n. 6, p. 8-pg., 2019-12-08.

Abstract

The trifluoromethyl anion (CF3-) displays C-13 NMR chemical shift (175.0 ppm) surprisingly larger than neutral (CHF3, 122.2 ppm) and cation (CF3+, 150.7 ppm) compounds. This unexpected deshielding effect for a carbanion is investigated by density functional theory calculations and decomposition analyses of the C-13 shielding tensor into localized molecular orbital contributions. The present work determines the shielding mechanisms involved in the observed behaviour of the fluorinated anion species, shedding light on the experimental NMR data and demystify the classical correlation between electron density and NMR chemical shift. The presence of fluorine atoms induces the carbon lone pair to create a paramagnetic shielding on the carbon nucleus. (AU)

• FAPESP's process: 15/08541-6 - Nuclear magnetic resonance spectroscopy: beyond molecular structure assignment
• Grantee: Claudio Francisco Tormena
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 17/20890-1 - Evaluation of shielding and transmission mechanisms of 1H, 13C and 19F NMR
• Grantee: Renan Vidal Viesser
• Support Opportunities: Scholarships in Brazil - Post-Doctoral