Abstract
Carbon-13 chemical shift assignments for nine 7,7-disubstituted 2,6-ditert-butylquinone methides of the types III-VI are reported. The 13C shifts of the exocyclic double bond carbon atoms are extraordinarily sensitive to C(7) substitution, viz. ΔδC(7) = 82.4 ppm and ΔδC(4) = 56.7 ppm on going from the dimethylamino to the cyano substituent. In contrast, electronic properties of the substituents are only weakly expressed on the carbonyl carbon atom. Satisfactory Swain-Lupton correlations were found for C(1), C(2) and C(4) chemical shifts yielding more than 50% of resonance contribution to the total transmission of substituent effects. Intercorrelations between the exocyclic double bond carbon chemical shifts of quinone methides and of identically substituted fulvenes as well as styrenes are also presented.
Published Version
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