Rates of Solvolysis of Substituted Phenyldimethylcarbinyl Chlorides in Methyl, Ethyl and Isopropyl Alcohols. Influence of the Solvent on the Value of the Electrophilic Substituent Constant<sup>1,2</sup>

Okamoto, Y.; Inukai, Takashi; Brown, Herbert C.

doi:10.1021/ja01551a053

Cited by 32 publications

(17 citation statements)

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“…While it is anticipated that an acid-catalyzed process would have a developing positive charge, the large magnitude of this influence was certainly surprising. As a point of comparison, the ρ + value for the solvolysis of cumyl chloride is −4.45, 48 which is considered to be an S N 1-like process, supporting the strong developing positive charge at the benzylic position in the transition state in acetal degradation. ( ii ) The relative positioning of the ketal moiety and the electron-withdrawing amido group can greatly influence its degradation, in that there is a two orders of magnitude difference in the cleavage rates of 2- and 6- carbon linkers.…”

Section: Resultsmentioning

confidence: 88%

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels

2017

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Effect of structural variations in acetal- and ketal- based linkers upon their degradation kinetics is studied through the design, synthesis and study of six series of molecules, comprising a total of eighteen different molecules. Through this systematic study, we show that the structural fine-tuning of the linkers allow access to variations in kinetics of degradation of more than six orders of magnitude. Hammett correlations show that the ρ value for the hydrolysis of benzylidene acetals is about −4.06, which is comparable to an SN1-like process. This shows that there is a strong, developing positive charge at the benzylic position in the transition state during the degradation of acetals. This positively charged transition state is consistent with the relative degradation rates of acetals vs. ketals (correlated to stabilities of 1°, 2°, and 3° carboxonium ion type intermediates) and the observed effect of proximal electron-withdrawing groups upon the degradation rates. Following this, we studied whether the degradation kinetics study correlates with pH-sensitive variations in the host-guest characteristics of polymeric nanogels that contains these acetal or ketal moieties as crosslinking functionalities. Indeed, the trends observed in the small molecule degradation have clear correlations with the encapsulation stability of guest molecules within these polymeric nanogels. The implications of this fundamental study extend to a broad range of applications, well beyond the polymeric nanogel examples studied here.

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Section: Resultsmentioning

confidence: 88%

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels

2017

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“…As Equation (2) includes both solvent and substituent effects on solvolytic reactivity, comparisons with simpler equations are important. Comparisons were made briefly with the Hammett–Brown11a, b ( ρ + σ + ) treatments of substituent effects,8a and various Grunwald–Winstein ( mY )12 correlations for solvent effects were shown 8b. Connections between Equation (2) and simpler equations11, 12 will now be explored further.…”

Section: Introductionmentioning

confidence: 99%

Additivity Rules Using Similarity Models for Chemical Reactivity: Calculation and Interpretation of Electrofugality and Nucleofugality

Bentley

2006

Chemistry A European J

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A recently proposed, multi-parameter correlation: log k (25 degrees C)=s(f) (Ef + Nf), where Ef is electrofugality and Nf is nucleofugality, for the substituent and solvent effects on the rate constants for solvolyses of benzhydryl and substituted benzhydryl substrates, is re-evaluated. A new formula (Ef=log k (RCl/EtOH/25 degrees C) -1.87), where RCl/EtOH refers to ethanolysis of chlorides, reproduces published values of Ef satisfactorily, avoids multi-parameter optimisations and provides additional values of Ef. From the formula for Ef, it is shown that the term (sfxEf) is compatible with the Hammett-Brown (rho+sigma+) equation for substituent effects. However, the previously published values of N(f) do not accurately account for solvent and leaving group effects (e.g. nucleofuge Cl or X), even for benzhydryl solvolyses; alternatively, if the more exact, two-parameter term, (sfxNf) is used, calculated effects are less accurate. A new formula (Nf=6.14 + log k(BX/any solvent/25 degrees C)), where BX refers to solvolysis of the parent benzhydryl as electrofuge, defines improved Nf values for benzhydryl substrates. The new formulae for Ef and Nf are consistent with an assumption that sf=1.00(,) and so improved correlations for benzhydryl substrates can be obtained from the additive formula: log k(RX/any solvent/25 degrees C)=(Ef + Nf). Possible extensions of this approach are also discussed.

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“…These data were used to determine s values using the expression s = log (k/k H )/ r, where r = À4.82 in methanol. 6 The rate retardation seen in the meta-derivative 10 corresponds to a s value of 0.20 for m-CH=N(O)-t-Bu (which is identical with the s I value). The more interesting rate behavior is seen in the p-CH=N(O)-t-Bu derivative 9, which is actually more reactive than the unsubstituted cumyl chloride 11.…”

Section: Results and Discussion Taft S I Value For Ch=n(o)-t-bumentioning

confidence: 70%

Electronic properties of the nitrone substituent. Stabilization of benzylic carbocations

Creary¹,

Hartandi²

2001

J. Phys. Org. Chem.

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Rates of Solvolysis of Substituted Phenyldimethylcarbinyl Chlorides in Methyl, Ethyl and Isopropyl Alcohols. Influence of the Solvent on the Value of the Electrophilic Substituent Constant^1,2

Cited by 32 publications

References 1 publication

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels

Additivity Rules Using Similarity Models for Chemical Reactivity: Calculation and Interpretation of Electrofugality and Nucleofugality

Electronic properties of the nitrone substituent. Stabilization of benzylic carbocations

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Rates of Solvolysis of Substituted Phenyldimethylcarbinyl Chlorides in Methyl, Ethyl and Isopropyl Alcohols. Influence of the Solvent on the Value of the Electrophilic Substituent Constant1,2

Cited by 32 publications

References 1 publication

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels

Substituent Effects on the pH Sensitivity of Acetals and Ketals and Their Correlation with Encapsulation Stability in Polymeric Nanogels

Additivity Rules Using Similarity Models for Chemical Reactivity: Calculation and Interpretation of Electrofugality and Nucleofugality

Electronic properties of the nitrone substituent. Stabilization of benzylic carbocations

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Product

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Rates of Solvolysis of Substituted Phenyldimethylcarbinyl Chlorides in Methyl, Ethyl and Isopropyl Alcohols. Influence of the Solvent on the Value of the Electrophilic Substituent Constant^1,2