Weakly nucleophilic leaving groups. Solvolyses of 1-adamantyl and t-butyl heptafluorobutyrates and trifluoroacetates

Bentley, T. William; Roberts, K.

doi:10.1039/p29890001055

Cited by 32 publications

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“…The operation of nucleophilic solvent assistance in the solvolyses of tert -butyl derivatives nicely explains [6–8] these observations. An alternative rationalization of these differences is to assume not enhanced nucleophilic participation by the solvent for the tert -butyl derivative solvolyses but enhanced electrophilic participation by the solvent for the 1-adamantyl derivative solvolyses [9–12].…”

Section: Introductionmentioning

confidence: 71%

“…An alternative rationalization of these differences is to assume not enhanced nucleophilic participation by the solvent for the tert -butyl derivative solvolyses but enhanced electrophilic participation by the solvent for the 1-adamantyl derivative solvolyses [9–12]. The observation that the 1-adamantyldimethylsulfonium ion shows little variation in its solvolyses rate in the commonly used solvents [7] but the tert -butyldimethylsulfonium ion shows increasing rate as the nucleophilicity of the solvent is increased [13] gives strong support to the proposed [6–8] nucleophilic solvent assistance to the solvolyses of the tert -butyl derivative. Indeed, the electrophilic participation by the solvent would be of little relevance when the leaving group initially has a formal positive charge on the atom adjacent to the α-carbon, such that it leaves as a neutral molecule.…”

Section: Introductionmentioning

confidence: 90%

“…A comparison of the reactivities of tert -butyl substrates with those for 1-adamantyl shows the tert -butyl substrate to be about a thousand times more reactive in ethanol [3] but solvolyses in the weakly nucleophilic 1,1,1,3,3,3,-hexafluoro-2-propanol (HFIP) occur at about the same rate [6–8]. The operation of nucleophilic solvent assistance in the solvolyses of tert -butyl derivatives nicely explains [6–8] these observations.…”

Section: Introductionmentioning

confidence: 99%

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Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

Kevill¹,

D’Souza²

2010

COC

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The original Grunwald-Winstein equation (1948) involved the development of a scale of solvent ionizing power (Y). Subsequent work has refined this scale and involved the development of scales of solvent nucleophilicity (N) and a term to correct for deviations when aromatic rings are present, governed by the aromatic ring parameter (I). These three scales, and the sensitivities towards each, can be related to specific rates of solvolysis through linear free energy relationships (LFERs). One important area of application of LFERs has been to the solvolyses of tert-alkyl halides. It has been proposed that the solvolysis of tert-butyl chloride involves a nucleophilic component, although other workers have suggested that the effects observed are related to electrophilic not nucleophilic influences. Takeuchi (1997) studied a compound with two of the methyl groups of tert-butyl chloride replaced by neopentyl groups. For this highly-hindered substrate there was no evidence for nucleophilic participation. Liu (1998) and Takeuchi (2001) have reported concerning the solvolyses of additional significantly-hindered tertiary alkyl chlorides. Liu (2009) has presented a parallel study of bromides. Martins (2008) has considered hindered tertiary alkyl halides, mainly with carbon-carbon multiple bonds as substituents. It was proposed that the hI term was of importance, with the sensitivities (h) sometimes positive and sometimes negative. To explain negative values, it was suggested that the I scale might contain a nucleophilicity component. In this review, we bring together, with analysis and commentary, the work of Takeuchi, Liu, Martins and others concerning the solvolyses of tertiary alkyl halides, with emphasis on the relevance of the three scales that have been developed for use in Grunwald-Winstein correlations.

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Section: Introductionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

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Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

Kevill¹,

D’Souza²

2010

COC

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“…In agreement with this observation, Bentley and Roberts reported a slope of 0.7 when solvolysis rates of 1adamantyl trifluoroacetate in a variety of solvents were plotted against the solvolysis rates of 1-adamantyl chloride (25 8C). [35] An analogous correlation between the solvolysis rate constants for 1-adamantyl picrate [36] and 1-adamantyl chloride, [9] with a slope of 0.5, reflects the even better delo-calization of charge density in the picrate leaving group. Because of the small number of data points for the correlations in Figure 3, we refrain from a quantitative discussion of the slopes.…”

Section: Resultsmentioning

confidence: 96%

Kinetics of the Solvolyses of Benzhydryl Derivatives: Basis for the Construction of a Comprehensive Nucleofugality Scale

Denegri

Streiter

Jurić

et al. 2006

Chemistry A European J

100

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A series of 21 benzhydrylium ions (diarylmethylium ions) are proposed as reference electrofuges for the development of a general nucleofugality scale, where nucleofugality refers to a combination of leaving group and solvent. A total of 167 solvolysis rate constants of benzhydrylium tosylates, bromides, chlorides, trifluoroacetates, 3,5‐dinitrobenzoates, and 4‐nitrobenzoates, two‐thirds of which have been determined during this work, were subjected to a least‐squares fit according to the correlation equation log k25 °C = sf(Nf + Ef), where sf and Nf are nucleofuge‐specific parameters and Ef is an electrofuge‐specific parameter. Although nucleofuges and electrofuges characterized in this way cover more than 12 orders of magnitude, a single set of the parameters, namely sf, Nf, and Ef, is sufficient to calculate the solvolysis rate constants at 25 °C with an accuracy of ±16 %. Because sf≈1 for all nucleofuges, that is, leaving group/solvent combinations, studied so far, qualitative discussions of nucleofugality can be based on Nf.

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“…Included in the study is a comparison with 1 (with larger chlorine atoms) and with the parent benzoyl chloride (with smaller hydrogen atoms in the ortho positions). [23][24][25][26][27][28] The behavior of 3 for most solvents was found to be very different to that of 2,6dichlorobenzoyl chloride (1). The (k 3 /k 1 ) specific rate ratios given in Table 1 for the solvolyses of 3 and 1 are extremely illuminating in this regard.…”

Section: Discussionmentioning

confidence: 99%

The importance of the ortho effect in the solvolyses of 2,6‐difluorobenzoyl chloride

Park

Kevill

2011

J of Physical Organic Chem

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The ortho effect of the chloro substituents in 2,6-dichlorobenzoyl chloride sufficiently hindered attack on the acyl carbon such that an ionization mechanism was observed over the full range of solvents studied. We now compare this behavior with that of 2,6-difluorobenzoyl chloride. The smaller fluoro substituents allow the dominant pathway to be addition-elimination (association-dissociation) in all solvents except those rich in fluoroalcohol, where ionization is dominant. Ranges of operation for both mechanisms had previously been observed for the parent benzoyl chloride but with a wider ionization range than for the 2,6-difluoro derivative. This indicates that, relative to the parent, the electronic destabilizing influence of the fluorines on acyl cation formation outweighs the steric retardation to attack because of the presence of the two ortho-fluorine atoms. An extended (two-term) Grunwald-Winstein equation treatment of the solvolyses of 2,6-difluorobenzoyl chloride is reported.

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Weakly nucleophilic leaving groups. Solvolyses of 1-adamantyl and t-butyl heptafluorobutyrates and trifluoroacetates

Cited by 32 publications

References 0 publications

Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

Use of the Simple and Extended Grunwald-Winstein Equations in the Correlation of the Rates of Solvolysis of Highly Hindered Tertiary Alkyl Derivatives

Kinetics of the Solvolyses of Benzhydryl Derivatives: Basis for the Construction of a Comprehensive Nucleofugality Scale

The importance of the ortho effect in the solvolyses of 2,6‐difluorobenzoyl chloride

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