Extended lithium ion pair indicator scale in tetrahydrofuran

Aggregation and Reactivity of the Lithium Enolate of 2-Biphenylylcyclohexanone in Tetrahydrofuran1

“…The indicator needs to have an acidity comparable to that of the substrate and a spectrum sufficiently different that both can be measured. A number of indicators are now known on the lithium ion pair scale in THF. , In eq 3, {RLi} denotes the formal concentration of the lithium enolate. The indicators are lithium salts of highly delocalized carbanions that are solvent separated ion pairs and have dissociation constants K diss ≅ 1 × 10 -5 M -1 in THF solution .…”

Ion Pair Acidities and Aggregation of Some Amide and Oxazoline Enolates in THF,

“…Ion Pair Acidity. Ion pair acidities are defined as the transmetalation equilibria in eq 1 (M = Li, Cs) using indicators, InH, of known p K values in THF; , the resulting Δp K 's are converted to absolute numbers 14 by setting the p K of fluorene equal to its ionic p K of 22.9 (per hydrogen) measured in DMSO …”

“…The existence of suitable absorption spectra for the ion pairs of compounds 1 − 7 allows the use of the double-indicator method of acidity determination, in which the concentrations of the ion pairs are determined by linear least-squares fitting of the spectra of the separate species (enolate and indicator) to the spectra of the equilibrium mixtures. Details of this method are reported elsewhere. − …”

Ion-Pair Acidity of Some Substituted Ferrocenes in Tetrahydrofuran. Stabilization of a Carbanion by Ferrocene1

“…Ion-pair acidity is defined as the transmetalation equilibrium in eq 1 where RH is the carbon acid whose p K is to be measured and InH is an indicator whose p K is on the established acidity scale. , …”

“…Compound 3 does not suffer such an entropy loss on deprotonation and should, therefore, be more acidic than otherwise expected. Note that 9-phenyl-10,10-dimethyldihydroanthracene 4 , in which two benzene rings are also held rigid, is 3 p K units more acidic than triphenylmethane …”