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Proximity and the heteroatom effects on the carbon‐13 chemical shifts of methyl‐substituted phenols, anilines and thiophenols
Author(s) -
Netzel Daniel A.
Publication year - 1978
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.1270110203
Subject(s) - aryl , chemistry , substituent , chemical shift , heteroatom , phenols , ring (chemistry) , medicinal chemistry , carbon fibers , organic chemistry , materials science , alkyl , composite number , composite material
Upfield substituent‐induced 13 C chemical shifts for aryl carbons of polymethyl substituted benzenes, phenols, anilines and thiophenols were investigated as a function of the proximity between substituents X and CH 3 (X = CH 3 , NH 2 , OH and SH). The results indicate that the induced shifts of the substituted aryl carbons are, in general, independent of the polar substituent but depend on the number of adjacent substituted aryl carbons. A −2.0 ppm upfield shift was found for a substituted aryl carbon adjacent to one substituted aryl carbon and a −3.8 ppm upfield shift for a substituted aryl carbon bound by two substituted aryl carbons. It is suggested that the near additivity of the upfield shifts is the result of changes in the bond order between the aromatic ring carbons in the region of the substituted aryl carbons due to distortion of the ring. The 13 C chemical shifts of the methyl substituents for methyl substituted phenols, anilines and thiophenols were determined, and it was found that the values could be predicted from the additivity parameters reported for the analogous methylbenzenes plus an additional pair‐interaction term associated with the through‐space electronic influence of the heteroatom.