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13 C and 19 F chemical shifts of bridgehead halogenated adamantanes
Author(s) -
Perkins Robert R.,
Pincock Richard E.
Publication year - 1976
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270080314
Subject(s) - chemical shift , halogen , chemistry , substituent , fluorine , additive function , stereochemistry , medicinal chemistry , organic chemistry , mathematical analysis , alkyl , mathematics
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.