## Abstract

A series of N-fluoroamide derivatives were synthesized by the reaction of CF_{3}OF with the corresponding amides. The reaction procedure of Barton et al.^{1} was appropriately modified to maximize the yield of the pure monofluoro derivatives. The compounds were examined as models for the determination of the Ø′ (^{3}Jhf) and ѱ′ (^{4J}_{HF}) angles of peptides with ^{1}H, ^{19}F, and ^{13}C NMR spectroscopy. Investigation of this series of compounds has led to Karplus-type relations between Ø′ vs. ^{3}J_{HF} and ѱ vs. ^{4}J_{HF} using the experimental coupling constants. As the signs of the coupling constants could not be determined at this time, several possibilities arise for these relations. Of these, the fitted equation (R = 0.990), ^{3}J_{NF-CH} ^{=} 70.8 cos^{2} Ø′ − 44.1 cos Ø′ − 7.2, best describes the angular relation for the Ø′ angle. The fitted equation (R = 0.983), ^{4}J_{NF-CO-CH} ^{=} −19.5 cos^{2} ѱ + 8.8 cos ѱ + 4.9, best describes the angular relation for the ѱ′ angle. The plots of both equations give typical Karplus curves except that they go through zero, i.e., undergo an inversion of sign. Fluorination of the amides causes the chemical shift of the carbonyl carbon to be shifted upfield 4–5 ppm while the carbon α to the nitrogen is shifted downfield 7–12 ppm. Furthermore, these carbons appear as doublets (^{2}J_{c-nf} ^{=} 4-9 Hz for the CᆖO and <1.0–14.7 Hz for Cα) because of their coupling with the fluorine atom. The ^{19}F chemical shifts of the model N-fluoroamide derivatives vary more than 39 ppm (δ_{F} 42 to 81 downfield of external CFC1_{3}) and are very sensitive to structural changes. It was not possible, however, to observe less than 5-Hz couplings in the ^{19}F spectra because of the quadrupolar broadening caused by the ^{14}N atom.

Original language | English (US) |
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Pages (from-to) | 1543-1552 |

Number of pages | 10 |

Journal | Journal of the American Chemical Society |

Volume | 106 |

Issue number | 6 |

DOIs | |

State | Published - Mar 1 1984 |

## ASJC Scopus subject areas

- Catalysis
- Chemistry(all)
- Biochemistry
- Colloid and Surface Chemistry

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