Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion^1,

Abstract

Spectral study of the cesium and lithium enolates of dibenzyl ketone (DBK) showed that both salts exist as contact ion pairs in THF solutions. The spectral data for the dicesium salt of DBK indicate that it exists as triple ions in which both cations are in contact with the dianion. The dilithium salt of DBK forms triple ions of two types in THF: in one, both cations are in contact with the DBK dianion, in the other, one of the lithium cations is solvent-separated. Evidence for dimerization of the ion pairs was obtained for both lithium and cesium enolates of DBK from UV-vis spectral (blue shift of the absorbance band at higher concentrations) and acidity (the decrease of pK at higher concentrations) studies. The dimerization constant for the cesium enolate of DBK obtained from the acidity data (3.5 x 10(3) M(-)(1)) is considered to be more accurate than that from the spectral analysis (1.7 x 10(3) M(-)(1)). The lithium enolate is much less dimerized than its cesium counterpart with a dimerization constant from acidity data of 4.2 x 10(2) M(-)(1). The first and second cesium pK values of DBK are 18.07 and 33.70, respectively, compared to the first lithium pK of 11.62.

Perspectives on Computational Organic Chemistry

“… (a) DMA = N,N-dimethylacetamide (b) Obtained by extrapolation (c) Ref 38 (d) Ref 39 (e) Ref 40 (f) Unpublished results (g) Ref 41 (h) Ref 42 (i) Ref 43 (j) Ref 44 (k) Ref 45 (l) Ref 46 (m) Ref 47 (n) Ref 48 (o) Ref 34, per hydrogen (p) For phenylacetylene (q) For aniline (r) For cyclohexyl phenyl ketone (s) For 1-indanone …”

Cs+/Alcohol Promoted[4C+2C]Annulation: ASynthetic Strategy for Polysubstituted Phenols

“…For the formation of 4 a (Scheme 5a), under the activation of the cesium ion, the dicesium salt I may be formed from 1 a with cesium ion in the presence of a base [19a] . The dicesium salt I might be stabilized by alcohol through chelating and attacks at the carbonyl carbon atom of 2 a to give intermediate II , where, an intramolecular cyclization occurs to form the unstable 2,3‐dihydro‐4 H ‐pyran‐4‐one III due to that III , as the ketene O,S ‐acetal, has two electron‐withdrawing groups [6] .…”

Nonlocal (Pair Site) Reactivity from Second-Order Static Density Response Function: Gas- and Solution-Phase Reactivity of the Acetaldehyde Enolate as a Test Case

“…13, 14 Several hypotheses have been advanced to pinpoint the factors controlling the ratios of C-alkylation to O-alkylation and the stereoelectronic factors governing the direction of attack on the enolate by the alkylating agent. 15,22 For instance, the introduction of metallic counterions into the substrate may favor either C-or O-alkylation by forming ion pair intermediates. 15,17 Solvent effect is also recognized as a determining factor controlling the kinetic products of alkylation.…”

“…15,22 For instance, the introduction of metallic counterions into the substrate may favor either C-or O-alkylation by forming ion pair intermediates. 15,17 Solvent effect is also recognized as a determining factor controlling the kinetic products of alkylation. 18,19 The nature of the electrophilic agent may also play a relevant role in the alkylation reaction of enolates.…”