| 1. |
- Prakash, G. K. Surya, et al.
(author)
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Long-Lived Trifluoromethanide Anion: A Key Intermediate in Nucleophilic Trifluoromethylations.
- 2014
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In: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 53:43, s. 11575-11578
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Journal article (peer-reviewed)abstract
- The trifluoromethanide anion is the postulated key intermediate in nucleophilic trifluoromethylation reactions. However, for more than six decades, the trifluoromethanide anion was widely believed to exist only as a short-lived transient species in the condensed phase. It has now been prepd. in bulk for the first time in THF soln. The trifluoromethanide anion with the [K(18-crown-6)]+ cation was unequivocally characterized by low-temp. 19F and 13C NMR spectroscopy. Its intermediacy in nucleophilic trifluoromethylation reactions was directly evident by its reaction chem. with various electrophilic substrates. Variable-temp. NMR spectroscopy, along with quantum mech. calcns., support the persistence of the trifluoromethanide anion. [on SciFinder(R)]
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| 2. |
- Prakash, G. K. Surya, et al.
(author)
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The Trifluoromethyl Group as a Conformational Stabilizer and Probe: Conformational Analysis of Cinchona Alkaloid Scaffolds.
- 2014
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 136:29, s. 10418-10431
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Journal article (peer-reviewed)abstract
- The introduction of the CF3 group on the C9 atom in quinidine can significantly increase the conformational interconversion barrier of the cinchona alkaloid scaffold. With this modification the conformational behavior of cinchona alkaloids in various solvents can be conveniently studied via 19F NMR spectroscopy. Based on the reliable conformational distribution information obtained, the accuracy of both theor. (PCM) and empirical (Kamlet-Taft) solvation models was assessed using linear free energy relation methods. The empirical solvation model provides accurate prediction of solvent effects, while PCM demonstrated a relatively low reliability. Using similar empirical solvation models along with Karplus-type equations, the conformational behavior of quinidine and 9-epi-quinidine also was studied. A model SN2 reaction was presented to reveal the important role of solvent-induced conformational behavior of cinchona alkaloids in their reactivity. [on SciFinder(R)]
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| 3. |
- Zhang, Zhe, et al.
(author)
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The Nucleophilicity of Persistent α-Monofluoromethide Anions.
- 2016
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In: Angewandte Chemie - International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55, s. 12845-12849
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Journal article (peer-reviewed)abstract
- α-Fluorocarbanions are key intermediates in nucleophilic fluoroalkylation reactions. Although frequently discussed, the origin of the fluorine effect on the reactivity of α-fluorinated CH acids has remained largely unexplored. We have now investigated the kinetics of a series of reactions of α-substituted carbanions with ref. electrophiles to elucidate the effects of α-F, α-Cl, and α-OMe substituents on the nucleophilic reactivities of carbanions. [on SciFinder(R)]
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