Ionizing Power of Aprotic Solvents

Streidl, Nicolas; Mayr, Herbert

doi:10.1002/ejoc.201001700

Cited by 15 publications

(16 citation statements)

References 55 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

Section: Electrofugalities: Rates Of Hydrolyses Of Trityl Derivativesmentioning

confidence: 61%

“…As previously reported for benzhydryl halides, ionization rate constants can also be measured in dipolar aprotic solvents when amines are present to trap the intermediate carbocations. [62] The lower graph of Fig. 6 shows that for [piperidine] 7 Â 10 À3 M, the conductimetrically determined ionization rates for (mF)(mF) 0 (mF) 00 Tr-Cl in acetonitrile are independent of the concentration of piperidine, indicating that ion recombination does not occur and that all carbocations generated are trapped by piperidine.…”

Section: Electrofugalities: Rates Of Hydrolyses Of Trityl Derivativesmentioning

confidence: 97%

See 1 more Smart Citation

A comprehensive view on stabilities and reactivities of triarylmethyl cations (tritylium ions)

Horn

Mayr

2012

J of Physical Organic Chem

Self Cite

View full text Add to dashboard Cite

By combining conventional photometric and conductimetric methods with stopped‐flow techniques, we were able to investigate ionization rate constants of trityl bromides, chlorides, and carboxylates in aqueous acetonitrile in a reactivity range from 10−5 to 103 s−1. In this way, it became possible to compare ionization processes yielding tritylium ions which differ by 21 units in pKR+, corresponding to 120 kJ mol−1 in free energy. Analysis of such far‐reaching correlations provided new insights into several aspects of organic reactivity. We observed (i) the change of solvolysis mechanisms from SN1 reactions without and with common ion return, (ii) reactions where formation and consumption of the carbocations could be observed visually, (iii) solvolyses where the ionization step is almost complete before the reaction with water becomes significant, and (iv) ionizations that yield solutions of persistent carbocations. The continuous change from reactions with carbocation‐like transition states to reactions with transition states of little carbocation character caused large variations of Winstein–Grunwald m values. Values of m = 0.2 for ionization processes show that low values of m do not necessarily imply SN2 reactions. Although the 4,4′,4″‐trimethoxytritylium ion reacts more than 1000 times faster with water than the 4‐dimethylaminotritylium ion and has a pKR+ value that is more negative by three units, both carbocations are formed with almost equal rates by ionization of the corresponding acetates in aqueous acetonitrile. This comparison again illustrates that electrofugality is not simply the inverse of electrophilicity and presents a challenge for further study of the importance of intrinsic barriers. Copyright © 2012 John Wiley & Sons, Ltd.

show abstract

Section: Electrofugalities: Rates Of Hydrolyses Of Trityl Derivativesmentioning

confidence: 61%

Section: Electrofugalities: Rates Of Hydrolyses Of Trityl Derivativesmentioning

confidence: 97%

A comprehensive view on stabilities and reactivities of triarylmethyl cations (tritylium ions)

Horn

Mayr

2012

J of Physical Organic Chem

Self Cite

View full text Add to dashboard Cite

show abstract

“…The latter dissociation of para ‐methoxy benzhydryl chloride occurs so easily, that Mayr et al were able to even measure kinetics of heterolyses in aprotic media. [62] Table 11 compares these results with computed values.…”

Section: Computational Methods and Accuracymentioning

confidence: 99%

Thermodynamics of chemical reactions with COSMO‐RS: The extreme case of charge separation or recombination

Deglmann

Schenk

2012

J Comput Chem

View full text Add to dashboard Cite

Many technically relevant chemical processes in the condensed phase involve as elementary reactive steps the formation of ions from neutral species or, as the opposite, recombination of ions. Such reactions that generate or annihilate charge defy the standard gas phase quantum chemical treatment, and also continuum solvation models are only partially able to account for the right amount of stabilization in solution. In this work, for such types of reaction, a solvation treatment involving the COSMO-RS method is assessed, which leads to improved results, i.e., errors of only around 10 kJ/mol for both protic and aprotic solvents. The examples discussed here comprise protolysis reactions and organo halide heterolysis, for both of which a comparison with reliable experimental data is possible. It is observed that for protolysis, the quality of results does not strongly depend on the quantum chemical method used for energy calculation. In contrast, in the case of heterolytic carbon-chlorine bond cleavage, clearly better results are obtained for higher correlated (coupled cluster) methods or the density functional M06-2X, which is well known for its accuracy if applied to organic chemistry. This hints at least that the right answer is obtained for the right reason and not due to a compensation of errors from gas phase thermodynamics with those from the solvation treatment. Problems encountered with certain critical solvents or upon decomposing Gibbs free energies into heats or entropies of reaction are found to relate mostly to the parameterization of the H-bonding term within COSMO-RS.

show abstract

“…91 The Hammett ρ values range from −4.0 to −4.3 in the different dipolar aprotic solvents, proving that the reactions occur by an S N 1 mechanism. The nucleofugality parameters (N f and s f from the log k = s f (E f + N f ) equation) for the diarylmethyl chlorides in CH 3 CN, DMA, DMSO, DMF, propylene carbonate, CHCl 3 , CH 2 Cl 2 , Nmethylpyrrolidine, and acetone have been determined.…”

Section: Medium Effects/solvent Effectsmentioning

confidence: 91%

Nucleophilic Aliphatic Substitution

Westaway¹

2014

Organic Reaction Mechanisms Series

View full text Add to dashboard Cite

Ionizing Power of Aprotic Solvents

Cited by 15 publications

References 55 publications

A comprehensive view on stabilities and reactivities of triarylmethyl cations (tritylium ions)

A comprehensive view on stabilities and reactivities of triarylmethyl cations (tritylium ions)

Thermodynamics of chemical reactions with COSMO‐RS: The extreme case of charge separation or recombination

Nucleophilic Aliphatic Substitution

Contact Info

Product

Resources

About