19F NMR Chemical Shift Table
Fluorine-19 (19F) nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique that leverages the unique properties of fluorine. With a nuclear spin of 1/2, high natural abundance (approximately 100%), and exceptional sensitivity - nearly 83% that of 1H-19F is an ideal nucleus for NMR studies. The chemical shift in 19F NMR arises from variations in the local electronic environment of fluorine nuclei.
- Shielding Effects: Electron-donating groups enhance shielding, causing upfield shifts (lower ppm values).
- Deshielding Effects: Electron-withdrawing groups reduce shielding, leading to downfield shifts (higher ppm values).
These effects are highly pronounced in 19F NMR because fluorine's electronegativity amplifies changes in electron density, creating significant and easily interpretable chemical shift ranges, typically from -200 ppm to +200 ppm.
Below is a comprehensive table summarizing typical 19F chemical shifts for various functional groups and fluorine compounds, referenced to trichlorofluoromethane (CFCl3, 0 ppm). These values are approximate and may vary with solvent, temperature, and molecular context.
Table of Chemical Shift Ranges
| Compound | Chemical Shift Range (ppm) vs. CFCl3 |
| -F-C=O | -70 to -20 |
| -CF3- | +40 to +80 |
| -CF2- | +80 to +140 |
| -CF- | +140 to +250 |
| -ArF- | +80 to +170 |
Table of Chemical Shift
| Compound | Chemical Shift (ppm) vs. CFCl3 |
| CFCl3 | 0 |
| MeF | -271.9 |
| CF3H (in CFCl3) | -78.6 |
| CF3H (in EtO) | -78.6 |
| CF2H2 | -143.6 |
| EtF | -213 |
| FCH=CH2 | -114 |
| F2C=CH2 | -81.3 |
| F2C=CF2 | -135 |
| CF3COOH (in CFCl3) | -76.55 |
| CF3COOH (neat) | -78.5 |
| CF3COOH (in CCl4） | -76.3 |
| CF3COOC6H6 | -73.85 |
| CF3COOCH2C6H6 | -75.02 |
| CF3COOCH3 | -74.21 |
| CF3COOEt (neat) | -78.7 |
| CF3COO(CH2)n | -74 to -75 |
| C6F6 | -164.9 |
| C6H5F | -113.5 |
| p-FC6H4F | -106 |
| CFH2Ph | -207 |
| C6H5CF3 | -63.72 |
| C4F8 | -135.15 |
| C5F10 | -132.9 |
| CF3R | -60 to -70 |
| CHF2OR | ~-82 |
| (CF3)2CO | -84.6 |
| CH2CN | -251 |
| F2 (elemental fluorine) | 422.92 |
| CF3Cl | -28.6 |
| ClF3 | +116, -4 |
| ClF5 | +247,+412 |
| CF2Cl2 | -8 |
| CFCl2CFCl2 | -67.8 |
| CFBr3 | 7.38 |
| CF2Br2 | 7 |
| IF4F(equatorial) | 58.9 |
| Aqueous F- (KF) | -125.3 |
| CH2FCN (monofluoro acetonitrile) | -251 |
| HF (aq) | -204 |
| IF7 | 170 |
| AsF3 | -40.6 |
| AsF5 | -66 |
| [AsF6]-1 | -69.5 |
| BF3 | -131.3 |
| (CH3)2O.BF3 | -158.3 |
| (C2H5)2O.BF3 | -153 |
| [BeF4]-1 | -163 |
| MoF6 | -278 |
| ReF7 | 345 |
| SF6 | 57.42 |
| SO2F | -78.5 |
| S2O5F2 | 47.2 |
| SbF5 | -108 |
| [SbF6]-1 | -109 |
| SeF6 | 55 |
| (C2H5)2SiF2 | -143 |
| SiF4 | -163.3 |
| [SiF6]-2 | -127 |
| TeF6 | -57 |
| WF6 | 166 |
| XeF2 | 258 |
| XeF4 | 438 |
| XeF6 | 550 |
| NF3 | 147 |
| SOF2 | 75.68 |
| C6H5SO2F (dilute) | 65.464 |
| C6H5SO2F (20% conc) | 65.514 |
| SF6 (dilute) | 57.617 |
| SF6 (10% conc) | 57.42 |
| SO2F2 | 33.17 |
| CBr3F (dilute) | 7.388 |
| CBr3F (80% conc) | 7.043 |
| CCl2F2 | -6.848 |
| CClF3 | -28.1 |
| PF3 | -34 |
| (CF3)3N (dilute) | -55.969 |
| (CF3)3N (30% conc) | -55.969 |
| CF3CF2CF2I | -60.47 |
| CF4 | -62.3 |
| C6H5CF3 (dilute) | -63.732 |
| C6H5CF3 (40% conc) | -63.37 |
| PF5 | -71.5 |
| CCl2F.CCl2F (dilute) | -67.775 |
| CCl2F.CCl2F (20% conc) | -67.834 |
| (CF3)3CF | -74.625 |
| CF3CO2H (dilute) | -76.53 |
| CF3CO2H (20% conc) | -76.542 |
| CF3(CF2)5CF3 | -81.6 |
| CF3(CF2)2CF3 | -81.85 |
| [CF3CF2CF2]N | -85.19 |
| POF3 | -90.7 |
| CF3CF2CF2CF2CN | -107.1 |
| CF3CF2CF2CF2CN | -105.764 |
Positive (+) values indicate downfield shifts, lower-shielding, or higher frequency.
Negative (-) values correspond to upfield shifts, higher-shielding, or lower frequency.
Factors Influencing 19F Chemical Shifts
The 19F chemical shift depends on several intrinsic and extrinsic factors:
a. Electronic Effects: The presence of strongly electronegative substituents, such as oxygen or nitrogen, can significantly deshield fluorine atoms, shifting the chemical shift downfield. Resonance effects within aromatic systems alter electron density, often inducing complex shifts in 19F signals.
b. Bonding and Hybridization: Fluorine attached to sp3 -hybridized carbon exhibits different shifts compared to those bonded to sp2- or sp-hybridized carbons due to changes in electron density.
c. Intermolecular Interactions: Hydrogen bonding, dipole-dipole interactions, or ion pairing can modify the local environment of fluorine atoms, causing deviations from expected shifts.
d. Temperature and Solvent Effects: Variations in temperature or solvent polarity influence fluorine's electronic surroundings, altering chemical shifts.
Applications of 19F Chemical Shifts
The broad and sensitive chemical shift range of 19F NMR enables its application in diverse scientific and industrial contexts:
- Organic Synthesis and Structural Elucidation
Fluorinated compounds are increasingly common in pharmaceuticals, agrochemicals, and materials science. 19F chemical shifts facilitate the identification of molecular frameworks, including stereochemistry and functional group placement.
- Pharmaceutical Development
Fluorine incorporation enhances drug properties like bioavailability and metabolic stability. 19F NMR tracks fluorinated drug metabolism and binding interactions, providing critical insights into drug design.
Fluorinated pollutants, such as perfluoroalkyl substances (PFAS), are analyzed using 19F NMR to assess their environmental impact and breakdown pathways.
Fluorinated polymers and advanced materials, such as perfluorinated membranes, benefit from 19F NMR to determine polymer structure, cross-linking, and crystallinity.
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