Experimental and Theoretical Characterization of the 3,5-Didehydrobenzoate Anion: A Negatively Charged meta-Benzyne
Price, J. M.; Nizzi, K. E.; Campbell, J. L.; Kenttämaa; H. I.;
Seierstad, M.; Cramer, C. J.
J. Am. Chem. Soc. 2003, 125, 131.
A negatively-charged analog of m-benzyne, 3,5-didehydrobenzoate, was synthesized in a Fourier transform ion cyclotron resonance mass spectrometer and its reactivity compared to the same ion generated previously in a flowing afterglow (FA) apparatus and to its positively-charged cousin, N-(3,5-didehydrophenyl)-3-fluoropyridinium. 3,5-didehyrdobenzoate was found to react as a nucleophile with electrophilic reagents. In contrast, N-(3,5-didehydrophenyl)-3-fluoropyridinium did not react the same electrophilic reagents but reacted instead with nucleophilic reagents. Neither ion is able to abstract hydrogen atoms from typical hydrogen atom donors. The absence of any radical reactivity for these m-benzynes is consistent with predictions that radical reactions singlet biradicals should be hindered compared to their monoradical counterparts. High-level calculations predict that the carboxylate moiety does not perturb the singlet-triplet gap of 3,5-didehydrobenzoate relative to the parent m-benzyne.
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