Do general nucleophilicity scales exist?

Mayr, Herbert; Ofial, Armin R.

doi:10.1002/poc.1325

Cited by 308 publications

(225 citation statements)

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“…The reactivities of electrophiles and nucleophiles thus studied cover a range of more than 30 orders of magnitude. [5] As bimolecular reactions in these solvents cannot be faster than 10 9 -10 10 L mol À1 s À1 (diffusion limit) and reactions slower than 10 À5 L mol À1 s À1 are difficult to measure, it is impossible to base a comprehensive nucleophilicity scale on measured rate constants for a single reference electrophile.…”

Section: The Patz-mayr Approachmentioning

confidence: 99%

Reply to T. W. Bentley: Limitations of the s(E+N) and Related Equations

Mayr

2011

Angew Chem Int Ed

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electrophilicity · kinetics · linear free-energy relationships · nucleophilicity · solvent effectsThe preceding commentary [1] is the forth in a series [2][3][4] that tries to discredit our approach to a semiquantitative model of polar organic reactivity. None of these publications reports new experimental results, and all deal exclusively with a reinterpretation of our kinetic data. As the detailed analysis of the manifold mistakes and incorrect statements in references [1][2][3][4] would bore the nonspecialist reader, I will comment the most important points in this response and ask the interested reader to find my comprehensive reply in the Supporting Information, which also provides a detailed validation of the statements in this reply. Let me first explain the essence of the controversy, which is not described in reference [1]. The Patz-Mayr ApproachIn recent years we have studied the kinetics of the reactions of carbocations and Michael acceptors with different types of nucleophiles, including alkenes, enol ethers, enamines, arenes, ylides, organometallic compounds, hydride donors, amines, phosphines, alcohols, alkoxides, and many more nucleophiles. The most commonly used solvents were dichloromethane, acetonitrile, DMSO, and water. The reactivities of electrophiles and nucleophiles thus studied cover a range of more than 30 orders of magnitude.[5] As bimolecular reactions in these solvents cannot be faster than 10 9 -10 10 L mol À1 s À1 (diffusion limit) and reactions slower than 10 À5 L mol À1 s À1 are difficult to measure, it is impossible to base a comprehensive nucleophilicity scale on measured rate constants for a single reference electrophile.Therefore, we have defined a series of benzhydrylium ions and quinone methides as reference electrophiles, which differ widely in reactivity. We studied the kinetics of their reactions with various nucleophiles and performed a least-squares minimization on the basis of Equation (1). [7a,b] In this equa-tion, electrophiles are characterized by one parameter (E), which we defined as solvent-independent, while nucleophiles are characterized by two parameters, the nucleophilicity parameter N and the nucleophile-specific sensitivity parameter s N (previously termed s), which are treated as solventdependent. Fixed parameters were E = 0 for (4-MeOC 6 H 4 ) 2 CH + and s N = 1.0 for 2-methyl-pent-1-ene. Reference [3] correctly describes that our basis correlation for deriving the reactivity parameters N, s N , and E was based on 209 rate constants for the reactions of 38 p nucleophiles with 23 electrophiles in the reactivity range À10 < E < 6. It is not clear why Scheme 1 in both Ref.[4] and Ref.[1] now pretend that our basis correlation was restricted to electrophiles in the narrow range of 0 < E < 6. This is not true![8] Details of our correlation are given in Appendix A of the Supporting Information.Since both s N and N are nucleophile-specific parameters, Equation (1) is equivalent to Equation (2), in which thenucleophilicity parameter Nu corresponds to log k of the...

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Section: The Patz-mayr Approachmentioning

confidence: 99%

Reply to T. W. Bentley: Limitations of the s(E+N) and Related Equations

Mayr

2011

Angew Chem Int Ed

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“…In the comparison of piperidine, piperazine, Nmethylpiperazine, and morpholine (Table 3), it is quite interesting and a wonder that only piperazine and N-methylpiperazine can be involved in such reactions, but the piperidine and morpholine cannot react with 4-chlorobenzyl cation to lose HCl. Experimental and theoretical studies indicate that the nucleophilicity of piperidine is stronger than that of piperazine [54,55], so the nucleophilicity is probably not the reason. When the amine is diethylamine, diisopropylamine, or pyrrolidine, the loss of HCl is not observed as well ( Figures S24-S26 in the online supplementary material).…”

Section: Nucleophilic Aromatic Substitutionmentioning

confidence: 99%

Gas-Phase Chemistry of Benzyl Cations in Dissociation ofN-Benzylammonium andN-Benzyliminium Ions Studied by Mass Spectrometry

Chai

Wang

Sun

et al. 2012

J. Am. Soc. Mass Spectrom.

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In this study, the fragmentation reactions of various N-benzylammonium and N-benzyliminium ions were investigated by electrospray ionization mass spectrometry. In general, the dissociation of N-benzylated cations generates benzyl cations easily. Formation of ion/neutral complex intermediates consisting of the benzyl cations and the neutral fragments was observed. The intra-complex reactions included electrophilic aromatic substitution, hydride transfer, electron transfer, proton transfer, and nucleophilic aromatic substitution. These five types of reactions almost covered all the potential reactivities of benzyl cations in chemical reactions. Benzyl cations are well-known as Lewis acid and electrophile in reactions, but the present study showed that the gas-phase reactivities of some suitably ring-substituted benzyl cations were far richer. The 4-methylbenzyl cation was found to react as a Brønsted acid, benzyl cations bearing a strong electron-withdrawing group were found to react as electron acceptors, and parahalogen-substituted benzyl cations could react as substrates for nucleophilic attack at the phenyl ring. The reactions of benzyl cations were also related to the neutral counterparts. For example, in electron transfer reaction, the neutral counterpart should have low ionization energy and in nucleophilic aromatic substitution reaction, the neutral counterpart should be piperazine or analogues. This study provided a panoramic view of the reactions of benzyl cations with neutral N-containing species in the gas phase.

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“…[7,9] Unfortunately, when the reaction was applied to thiophenes only traces of 3 a were observed under the reaction conditions ( [3][4][5][6][7][8]. The best result (84 % yield) was obtained with trifluoroacetic acid (TFA; 1 equivalent with respect to 1).…”

Section: Jonathan P Brand and Jørôme Waser*mentioning

confidence: 85%

“…In fact, the extension of known alkynylation methodologies to thiophene is not easy, because of its low reactivity. [4,8] Herein, we report the alkynylation of thiophenes by using 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1H)-one (TIPS-EBX; 1). The reaction proceeded at room temperature under air [Eq.…”

Section: Jonathan P Brand and Jørôme Waser*mentioning

confidence: 99%