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13C and 19F chemical shifts of bridgehead halogenated adamantanes

✍ Scribed by Robert R. Perkins; Richard E. Pincock

Publisher
John Wiley and Sons
Year
1976
Tongue
English
Weight
536 KB
Volume
8
Category
Article
ISSN
0749-1581

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✦ Synopsis

Abstract

The ^13^C chemical shifts of the sixteen bridgehead substituted mono‐, di‐, tri‐ and tetrahaloadamantanes (halo = F, Cl, Br, I) and four mixed 1,3‐dihaloadamantanes are reported. The effect of bridgehead halogens on the shift values of carbons in β and δ positions is well correlated by the simple additivity relationship based on substituent shifts of 1‐monohaloadamantanes. A substituted α‐carbon is shifted upfield with an increase in the number of halogens at other bridgehead positions and this shift is relatively greater in the order F < Cl < Br < I. This observed upfield shift of α‐carbons is opposite to the downfield shift expected from additivity. An unsubstituted bridgehead γ‐carbon is moved to lower fields by one, two and three bromines (or iodines) at other bridge‐heads while, in contrast, a third fluorine weakly shields the remaining unsubstituted γ‐carbon. Some special noncumulative effects of halogens operating across the 1,3‐bridgehead positions of adamantane are indicated by the data. The ^19^F chemical shifts of 1‐fluoro‐, 1,3‐difluoro‐, 1,3,5‐trifluoro‐ and 1,3,5,7‐tetrafluoroadamantanes are contrary to expectations based on inductive effects in that they move progressively upfield. Other 1‐fluoroadamantanes with chloro, bromo, or methyl groups present also show substituent‐induced chemical shifts which shield the fluorine.

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