Concerning negligible aqueous solvent effects on proton transfer equilibrums of aryl carbocations

Wolf, J. Frederick; Harch, Paul G.; Taft, Robert W.

doi:10.1021/ja00843a051

Cited by 36 publications

(17 citation statements)

References 1 publication

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“…We, therefore, conclude that the proton of PSH+ is involved in a strong intramolecular H-bond which precludes H-bonding to water, or even to more basic Me2S0 as we have seen. Further support of this point comes from the remarkable correlation of Taft et al (23) which suggests that the solvation behaviour of PSH+ in water is more like that of resonance-stabilized carbonium ions.…”

Section: Enthalpies Of Transfermentioning

confidence: 88%

Basicity of 1,8-bis(dimethylamino)naphthalene and 1,4-diazabicyclo[2.2.2]octane in water and dimethylsulfoxide

Benoit¹,

Lefebvre²,

Fréchette³

1987

Can. J. Chem.

114

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. 65, 996 (1987). The ionization constants of the conjugate acids BH:' of two bases widely used in synthesis, 1,8-bis(dimethy1amino)naphthalene (PS), and 1,4-diazabicyclo[2.2.2]octane (DABCO), have been obtained in Me2S0 and water. The partition coefficients of both bases B and their heats of solution and protonation have also been determined. The basicity of PS is dramatically reduced when passing from water to Me2S0 while the basicity of DABCO remains unchanged, thus making DABCO the stronger base in Me2S0. The solvent effect on the base strength is analyzed in terms of free energy and enthalpy of transfer for B and H', and for BH', from water to Me2S0. The entropy-controlled much stronger solvation of PS in Me2S0 is in line with that of aromatic compounds while the increased solvation of DABCO in water is due to H-bonding of its two nitrogens. PSH', like H + , is better solvated by Me2S0 while DABCOH' does not show a definite preference for one solvent. The calculated enthalpy of solution of gaseous PSH' is abnormally low when compared to that of DABCOH+ and of related BH+ ions, thus indicating that the proton of PSH', in a strong intramolecular H-bond, does not normally H-bond to the solvent. Our results suggest that the proton sponge acid-base system could be used as a convenient reference to determine the free energy and enthalpy of transfer of H' between solvents.

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Section: Enthalpies Of Transfermentioning

confidence: 88%

Basicity of 1,8-bis(dimethylamino)naphthalene and 1,4-diazabicyclo[2.2.2]octane in water and dimethylsulfoxide

Benoit¹,

Lefebvre²,

Fréchette³

1987

Can. J. Chem.

114

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“…Such a phenomenon has been proposed for larger carbocations in which the close quantitative analogy between gas-phase stability order and that in nonaqueous solution was rationalized in this way. [38] A second, more likely, explanation relies on the reactions themselves. Whereas nucleophilic substitution or carbonyl addition reactions are inherently polar reactions in which the charge distribution, and hence polar solvation, changes dramatically on going from starting material, to transition state, to product, typical organometallic reactions, such as p complexation, oxidative addition, or reductive elimination, are largely nonpolar reactions in which the charge plays only a spectator role.…”

Section: Catalyst Screeningmentioning

confidence: 99%

Electrospray Ionization Tandem Mass Spectrometry in High‐Throughput Screening of Homogeneous Catalysts

2003

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The frontispiece shows an illustration by John Tenniel and an excerpt from the 1865 edition of Lewis Carroll's "Alice in Wonderland". Because everything in Wonderland runs counter to logic, the Queen of Hearts declares in Alice's trial "Sentence first-verdict afterwards". High-throughput screening of catalysts, as it is conventionally practiced, does "Synthesis first-screening afterwards" which, as is argued in this review, also backwards. Given the particular constraints present in organometallic complexes, it is more efficient to develop a selective synthesis only when it has already been determined that a structure is likely to be better. The consequence is that screening methods must be able to handle ill-defined mixtures. Electrospray ionization tandem mass spectrometry is presented as a technical solution to this problem.

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“…Eine Möglichkeit wäre, dass die untersuchten Moleküle eine Größe erreicht haben, aufgrund der ein intramolekulares Äquivalent der Solvatation vorliegt. Das Argument wurde für größere Carbokationen herangezogen, um die weitgehend quantitative Übereinstimmung zwischen der Stabilitätsreihe in der Gasphase und der in nichtwässriger Lösung zu erklären 38. Eine zweite, wahrscheinlichere Erklärung stützt sich auf den individuellen Reaktionstyp.…”

Section: Elektrosprayionisierungs‐tandem‐massenspektrometrie Als Eunclassified

Elektrosprayionisierungs‐Tandem‐Massenspektrometrie im Hochdurchsatz‐Screening homogener Katalysatoren

Chen

2003

Angewandte Chemie

130

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Der Vortitel enthält eine Illustration von John Tenniel und einen Auszug aus “Alice im Wunderland” von Lewis Carroll in der Ausgabe von 1865. Weil alles im Wunderland der Logik widerspricht, erklärt die Königin im Prozess gegen Alice: “Zuerst die Strafe, dann das Urteil!” Das üblicherweise praktizierte Hochdurchsatz‐Screening von Katalysatoren beruht auf dem Prinzip “zuerst die Synthese, dann das Screening”, worin, wie in diesem Aufsatz diskutiert wird, ebenfalls die Logik umgekehrt ist. Unter den besonderen Zwangsbedingungen für metallorganische Komplexe ist es effizienter, eine selektive Synthese erst dann zu entwickeln, wenn eine bestimmte Struktur der katalytisch aktivste Kandidat unter vielen zu sein scheint. Demzufolge müssen Screening‐Methoden auch für schlecht definierte Mischungen geeignet sein. Die Elektrosprayionisierungs‐Tandem‐Massenspektrometrie bietet eine ausgezeichnete technische Lösung für dieses Problem.

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Concerning negligible aqueous solvent effects on proton transfer equilibrums of aryl carbocations

Cited by 36 publications

References 1 publication

Basicity of 1,8-bis(dimethylamino)naphthalene and 1,4-diazabicyclo[2.2.2]octane in water and dimethylsulfoxide

Basicity of 1,8-bis(dimethylamino)naphthalene and 1,4-diazabicyclo[2.2.2]octane in water and dimethylsulfoxide

Electrospray Ionization Tandem Mass Spectrometry in High‐Throughput Screening of Homogeneous Catalysts

Elektrosprayionisierungs‐Tandem‐Massenspektrometrie im Hochdurchsatz‐Screening homogener Katalysatoren

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