29/28, 30/28Silicon, 34/32sulfur and 80/77selenium isotope‐induced fluorine chemical shifts through two bonds

Tordeux, Marc; Magnier, Emmanuel; Guidotti, Jérôme; Diter, Patrick; Wakselman, Claude

doi:10.1002/mrc.1422

Cited by 6 publications

(4 citation statements)

References 20 publications

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“…Replacement of 12 C with 13 C on one of the CF carbons shifts the directly attached fluorine upfield by ca. 0.1 ppm, due to an isotope effect, and removes the chemical shift equivalence. The resulting doublets in F2 , from the F–C–C– 13 C– F isotopomer are shifted upfield and are ca.…”

Section: Resultsmentioning

confidence: 91%

Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene

et al. 2015

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A conformational analysis of o-fluoro Z-azobenzene reveals a slight preference for aromatic C-F/π interaction. Density functional theory (DFT) indicates that the conformation with a C-F/π interaction is preferred by approximately 0.3-0.5 kcal/mol. Ground-state conformations were corroborated with X-ray crystallography. (Z)-Azobenzene (Z-AB) with at least one o-fluoro per ring displays (19)F-(19)F through-space (TS) coupling. 2D J-resolved NMR was used to distinguish through-bond from TS coupling ((TS)JFF). (TS)JFF decreases as the temperature is lowered and the multiplets coalesce into broad singlets. We hypothesize that the coalescence temperature (Tc) corresponds to the barrier for phenyl rotation. The experimentally determined barrier of 8-10 kcal/mol has been qualitatively verified by DFT where transition states with a bisected geometry were identified with zero-point energies of 6-9 kcal/mol relative to ground state. These values are significantly higher that values estimated from previous theoretical studies but lie within a reasonable range for phenyl rotation in hydrocarbon systems.

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Section: Resultsmentioning

confidence: 91%

Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene

et al. 2015

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“…Two-bond 19 F-12 C/ 13 C isotope shifts for similar structures are reported to be 0.010-0.015 ppm and are below the error of the chemical shift measurements in these 2D experiments. [23] In the spectra A 2 , A 3 and a 2 groups all exhibit only single sets of 13 C chemical shifts. There are three stereogenic centers in the K 4 sample; however, they do not influence the A chain-end 13 C shifts.…”

Section: F{ 13 C} Ghsqc 2d-nmrmentioning

confidence: 99%

“…Note that the 19 F shifts in the 1 J CF HSQC spectra are offset by −0.10 ± 0.01 ppm compared with their corresponding 19 F shift in the 2 J CF HSQC. [23] This is due to a large 13 C isotope shift of the 19 F resonance for the former correlation. In the 1 J CF HSQC, the cross-peaks come from 19 F directly bound to 13 C. By comparison, in the 2 J CF HSQC experiment, cross-peaks are from 19 F directly bound to 12 C and are two bonds away from 13 C. This isotope shift is identical for the resonances of all the structure units in this compound and is easily taken into account when interpreting the NMR data for this class of fluoropolymers.…”

Section: Assignment Of a Unitsmentioning

confidence: 99%

2D‐NMR studies of a model for Krytox^® fluoropolymers

McCord

Baiagern

et al. 2011

Magnetic Reson in Chemistry

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Multiple two-dimensional nuclear magnetic resonance (2D-NMR) techniques have been used to study the structures of Krytox(®) perfluoro(polyalkyl ether) and its mechanism of polymerization. Model compound K(4), containing four Krytox(®) fluoropolymer repeat units, was analyzed to interpret the multiplet patterns in the NMR spectra from the polymer model. (19)F {(13)C}-Heteronuclear single-quantum correlation experiments, performed with delays optimized for (1)J(CF) and (2)J(CF), provided spectra that permitted identification of resonances from individual monomer units. Selective, (19)F-(19)F COSY 2D-NMR experiments were performed with different excitation regions; these experiments were combined with selective inversion pulses to remove (19)F-(19)F J couplings in the f(1) dimension. The resulting COSY spectra were greatly simplified compared with standard (19)F-(19)F COSY spectra, which are too complicated to interpret. They give information regarding the attachments of monomer units and also provide insights into the nature of the stereoisomers that might be present in the polymer. Both infrared and NMR spectra show peaks identifying chain end structures. With the help of these studies, resonances can be assigned, and the average number of repeat units in the polymer chain can be calculated based on the assignments obtained.

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“…Note that the 19 F bound to 13 C (top) is shifted by ca. 0.1ppm upfield compared the the 19 F bound to 12 C as a result of the well-known isotope shift (25). Many regions such as this were identified in the HSQC spectra, in order to identify resonances from each of the unique structure fragments in tHFPO.…”

Section: Characterization Of Phfpo Structurementioning

confidence: 99%

Advanced Solution 2D-NMR of Fluoropolymers

Rinaldi

Baiagern

Fox

et al. 2011

ACS Symposium Series

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C heteronuclear single quantum correlation (HSQC) 2D-NMR experiments based on 1 J CF and 2 J CF experiments provide short range correlations within monomer units and in many cases help to distinguish between structure fragments identified using 3 J FF , 4 J FF and 5 J FF correlations. COSY and especially selective COSY experiments provide high resolution 2D-NMR experiments with correlations based on 3 J FF , 4 J FF and 5 J FF couplings. These permit identification of long-range structure correlations between monomer units. Examples using poly(hexafluoropropylene oxide) and poly(vinylidene fluoride) are shown.

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^29/28, ^30/28Silicon, ^34/32sulfur and ^80/77selenium isotope‐induced fluorine chemical shifts through two bonds

Cited by 6 publications

References 20 publications

Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene

Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene

2D‐NMR studies of a model for Krytox^® fluoropolymers

Advanced Solution 2D-NMR of Fluoropolymers

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29/28, 30/28Silicon, 34/32sulfur and 80/77selenium isotope‐induced fluorine chemical shifts through two bonds

Cited by 6 publications

References 20 publications

Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene

Conformational Dynamics of o-Fluoro-Substituted Z-Azobenzene

2D‐NMR studies of a model for Krytox® fluoropolymers

Advanced Solution 2D-NMR of Fluoropolymers

Contact Info

Product

Resources

About

^29/28, ^30/28Silicon, ^34/32sulfur and ^80/77selenium isotope‐induced fluorine chemical shifts through two bonds

2D‐NMR studies of a model for Krytox^® fluoropolymers