Abstract
The nucleophilic character and stability of the carbanions vs. alkoxides derived from 2,2,2-trifluoro-1-(9-anthryl)ethanol and 1-(9-anthryl)ethanol containing X electron-releasing and X electron-acceptor substituents attached to C-10, have been studied at the B3LYP/6-31+G(d,p) level of theory. Results analyzed in terms of the absolute gas-phase acidity, Fukui function, the local hard and soft acids and bases principle, and the molecular electrostatic potential, show that the central ring of the 9-anthryl group confers an ambident nucleophilic character and stabilizes the conjugated carbanion by electron-acceptor delocalization.
Highlights
Pure enantiomers of 2,2,2-trifluoro-1-(9-anthryl)ethanol (1a, Figure 1), are mainly used as chiral solvating agents [1,2] and chiral selectors [1,2,3,4] due to their particular hydroxyl (OH) and methine (CH) acidity [5,6,7,8]
The CH acidity is higher than the OH acidity for 1e–1g and 2b–2g, which implies that the carbanions 1e–1g and 2b–2g are more stable than the alkoxides by 3.1–12.4 and 3.8–26.1 kcal mol−1 respectively
The nucleophilic character and the relative stability of the carbanions vs. the corresponding alkoxides of 1-(9-anthryl)ethanol and its derivatives has been studied in terms of the absolute gas phase acidity, Fukui function, the local hard and soft acids and bases principle (HSAB) bases principle and the molecular electrostatic potential
Summary
Pure enantiomers of 2,2,2-trifluoro-1-(9-anthryl)ethanol (1a, Figure 1), are mainly used as chiral solvating agents [1,2] and chiral selectors [1,2,3,4] due to their particular hydroxyl (OH) and methine (CH) acidity [5,6,7,8]. These results imply that the anthryl ring stabilizes more efficiently the negative charge in the carbanion than the alkoxide (Scheme 1). The resonance effects on the alkoxide are absent; while the resonance effects on the carbanion are present and the negative charge ought to be delocalized mainly on the C-11 and C-10 carbon atoms. An ambident nucleophilic character should be observed for the carbanion, and there would be an electrophilic attack on the C-11 and C-10 carbon atoms
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