Lithium and Cesium Ion-Pair Acidities of Some Terminal Acetylenes and Aggregation in Tetrahydrofuran<sup>1</sup>

Gareyev, Roustam; Streitwieser, Andrew

doi:10.1021/jo951243q

Cited by 22 publications

(19 citation statements)

References 29 publications

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“…Experimental p K values at different concentrations of CsDBK are presented in Table S2. The decrease of the observed p K with increasing formal concentration of corresponding salt was shown previously for ketones , and other compounds , to result from aggregation of ion pairs to dimers or higher aggregates. The aggregation shifts the equilibrium 2 to the right, increasing the apparent K .…”

Section: Resultssupporting

confidence: 78%

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion¹^,

1996

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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.

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Section: Resultssupporting

confidence: 78%

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion¹^,

1996

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“…Recent computations show that solvation by H 2 O molecules has sufficient energy to overcome the π-interactions between lithiums and the triple bonds in ( 1-Li ) 2 …”

Section: Resultsmentioning

confidence: 99%

Alkali Metal Cation π-Interactions in Metalated and Nonmetalated Acetylenes: π-Bonded Lithiums in the X-ray Crystal Structures of [Li−C⋮C−SiMe₂−C₆H₄−OMe]₆and [Li−O−CMe₂−C⋮C−H]₆and Computational Studies

1997

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The X-ray crystal structure of [Li−C⋮C−SiMe2−C6H4−OMe]6 (14)6 features nearly symmetric π-interactions between the lithium ions and the acetylide anions (Li1−Cβ = 2.353(9) Å, Li1−Cα = 2.292(9) Å). These π-contacts are facilitated by the chelating o-anisyl methoxy groups (Li1−Cα−Cβ = 77.6(4)°, Li1−O1 = 2.169(9) Å). The Li−Cα distances in the (LiCα)6 core of (14)6 differ significantly (Li1α−Cα = 2.132(9) Å, Li1b−Cα = 2.205(11) Å). This Li−Cα distance differentiation is unique in organolithium hexamers, and is due to Li(C⋮C−R) “side-on-π” and “end-on-σ” contacts, as is shown computationally in H−C⋮C−Li(LiH)2 (20). A second X-ray crystal structure, [Li−O−CMe2−C⋮C−H]6 (22)6, reveals electrostatic π-interactions between the lithiums in the (LiO)6 core and the nonmetalated acetylene groups (Li1−C2 = 2.443(5) Å, Li1−C3 = 2.749(6) Å). These Li−C π-contacts shorten upon acetylene lithiation, as is shown computationally in Li−O−CH2−C⋮C−(H/Li) (24-H/Li). Additional computations reveal that the π-interactions in (HC⋮C)M2H (26-Li-Cs) complexes (modelling oligo- and polymeric M−C⋮C−R) are weak (only 0.7 kcal/mol for Li), but substantial in M+(H−C⋮C−H) (27-Li-Cs) species (20.2 kcal/mol for Li+). In 26-Li-Cs, the π-contacts increase the C⋮C bond lengths slightly (0.005 Å for Li) and lower the C⋮C stretching frequencies (33 cm-1 for Li), they polarize charge density from Cα toward Cβ and hence result in counterion-induced charge delocalizations. The degrees of π-interactions both in (26-Li-Cs) and in (27-Li-Cs) decrease with increasing size of the alkali cations.

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“… (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 …”

Section: Figures and Tablesmentioning

confidence: 99%

Perspectives on Computational Organic Chemistry

Streitwieser

2009

J. Org. Chem.

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The author reviews how his early love for theoretical organic chemistry led to experimental research and the extended search for quantitative correlations between experiment and quantum calculations. The experimental work led to ion pair acidities of alkali-organic compounds and most recently to equilibria and reactions of lithium and cesium enolates in THF. This chemistry is now being modeled by ab initio calculations. An important consideration is the treatment of solvation in which coordination of the alkali cation with the ether solvent plays a major role.

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Lithium and Cesium Ion-Pair Acidities of Some Terminal Acetylenes and Aggregation in Tetrahydrofuran¹

Cited by 22 publications

References 29 publications

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion¹^,

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion¹^,

Alkali Metal Cation π-Interactions in Metalated and Nonmetalated Acetylenes: π-Bonded Lithiums in the X-ray Crystal Structures of [Li−C⋮C−SiMe₂−C₆H₄−OMe]₆and [Li−O−CMe₂−C⋮C−H]₆and Computational Studies

Perspectives on Computational Organic Chemistry

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Lithium and Cesium Ion-Pair Acidities of Some Terminal Acetylenes and Aggregation in Tetrahydrofuran1

Cited by 22 publications

References 29 publications

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion1,

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion1,

Alkali Metal Cation π-Interactions in Metalated and Nonmetalated Acetylenes: π-Bonded Lithiums in the X-ray Crystal Structures of [Li−C⋮C−SiMe2−C6H4−OMe]6and [Li−O−CMe2−C⋮C−H]6and Computational Studies

Perspectives on Computational Organic Chemistry

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Lithium and Cesium Ion-Pair Acidities of Some Terminal Acetylenes and Aggregation in Tetrahydrofuran¹

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion¹^,

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion¹^,

Alkali Metal Cation π-Interactions in Metalated and Nonmetalated Acetylenes: π-Bonded Lithiums in the X-ray Crystal Structures of [Li−C⋮C−SiMe₂−C₆H₄−OMe]₆and [Li−O−CMe₂−C⋮C−H]₆and Computational Studies