ISSN:
0749-1581
Keywords:
NMR
;
19F NMR
;
chlorine isotope shift
;
bromine isotope shift
;
substituted fluorobenzenes
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Long-range isotope shifts, Δδ, due to 37Cl/35Cl and 81Br/79Br, in the 19F NMR spectra of some substituted benzenes are reported. The shifts appear to be invariant to solvent and are additive when the isotopes are in chemically equivalent positions relative to the fluorine site. The three-bond isotope shift attributed to chlorine is approximately -1.60 ppb and that from bromine varies from -0.25 to -0.28 ppb. These shifts appear to be invariant to the substituent pattern. However, there is a large difference in the four-bond shift for 2,6-dichloro-4-fluorophenol (-0.16 ppb) and 2-chloro-6-fluorocyanobenzene, (-0.55 ppb), suggesting that this isotope shift is mediated by the intervening group. In all cases, substitution by the heavier chlorine isotope resulted in increased shielding. The nearly equal natural abundance of 81Br and 79Br resulted in double peaks of approximately equal intensity. However, in almost all cases, the high-field peak is of slightly lower intensity, suggesting that the sign of this isotope effect is also negative.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260331107
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