Nucleofugalities of Neutral Leaving Groups in 80 % Aqueous Acetonitrile

Jurić, Sandra; Portolan, Toni; Kronja, Olga

doi:10.5562/cca2822

Cited by 5 publications

(11 citation statements)

References 13 publications

(73 reference statements)

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“…Similarly, as in our previous works for solvolyses with positively charged substrates (pyridinium, [ 8 ] dimethylsulfonium, [ 12a ] and tetrahydrothiophenium [ 12b ] salts), a very small variation of the rate of S N 1 reaction with solvent variation was found for solvolysis of 4‐methoxypyridinium ions (Table 1). The solvolysis rates of 4‐methoxypyridinium ions slightly decrease as the solvent polarity increases, which is in line with Hughes–Ingold rule.…”

Section: Resultssupporting

confidence: 80%

“…Similarly, we determined nucleofugality in water of 4‐chloropyridine in combination with 4,4′‐bis(morpholino)benzhydrilium ion to be −2.95 and the nucleofugality of pyridine in combination with 4,4′‐bis (methylamino)benzhydrylium ion to be equivalent to −4.00. [ 8a ]…”

Section: Resultsmentioning

confidence: 99%

“…The values of s f determined for 4‐methoxypyridinium ion are somewhat smaller (average s f = 1.08) than the s f values obtained earlier for 4‐chloropyridinium (average s f = 1.16) and pyridinium (average s f = 1.12) ions in which the values of s f indicate development of a positive charge on the benzhydrylium ion in the TS reaction. [ 8 ] Keeping in mind that ferrocenylphenylmethyl derivatives solvolyze faster than the corresponding benhydryl derivatives, this can be explained due to a somewhat earlier transition state in the heterolytic step of ferrocenylphenylmethylpyridinium salts and delocalization of the positive charge generated on the carbon atom of the reaction center in the transition state to ferrocenyl group. Due to the strong electron‐donating ability of the ferrocenyl group, a reduction of the positive charge on the reaction center in the transition state occurs.…”

Section: Resultsmentioning

confidence: 99%

“…In our previous works, the leaving group abilities of differently 4‐X‐substituted pyridines (X = Cl, H, CH 3 ) in S N 1 solvolytic reactions have been determined by analyzing the rate constants of X,Y‐substituted benzhydrylpyridinium salts obtained in various solvents. [ 8 ] To obtain a complete profile of uncharged leaving groups (differently substituted pyridines), we investigated the heterolytic bond breaking of ferrocenylphenylmethyl‐4‐methoxypyridinium derivatives and formation of the free 4‐methoxypyridine and differently substituted ferrocenylphenylmethyl ions in the rate‐determining step of the S N 1 reaction (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

“…Up to now, the least reactive neutral nucleofuges on the nucleofugality scale developed in line with Equation are 4‐chloropyridine ( N f from −0.95 to −1.37 in various solvents), pyridine ( N f from −2.28 to −3.22 in various solvents), and 4‐methylpyridine ( N f from −3.06 to −4.20 in various solvents). [ 8 ] Nucleofuge‐specific parameters ( N f and s f ) in various solvents for the respective nucleofuges were derived from log k versus E f plots (Equation ) using benzhydryl cations ( E f ≤ 0) as electrofuges. Keeping in mind that the electron‐accepting group on the 4‐position of the pyridine ring increases the rate of the heterolysis step in pyridinium salts, 4‐methoxypyridine of benzhydryl cations with E f ≤ 0 solvolyze too slowly.…”

Section: Introductionmentioning

confidence: 99%

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Solvolytic behavior of some ferrocenylphenylmethyl‐4‐methoxypyridinium cations in various solvents

Jurić

2022

J of Physical Organic Chem

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The nucleofugalities of 4‐methoxypyridine (4‐OMePy) in pure and aqueous solvents were derived from the rate constants for SN1 solvolysis with respect to the corresponding ferrocenylphenylmethyl‐4‐methoxypyridinium salts by applying the linear free energy relationship (LFER) equation, log k (25°C) = sf (Nf + Ef). In more polar solvents, pyridinium ions become more stabilized by solvation in the reactant ground state than in the corresponding transition state and the reactivity (nucleofugality, Nf) of 4‐OMePy decreases increasing solvent polarity. Due to the strong electron‐donor effect of the ferrocenyl group, it seems that 4‐methoxypyridine is a somewhat better leaving group (stronger nucleofuge) if the substrate is benzhydryl‐4‐methoxypyridinium salts rather than ferrocenylphenylmethyl‐4‐methoxypyridinium salts. Given that the electron‐withdrawing substituents on the 4‐position of the pyridine ring increase the rate of the heterolysis step of solvolysis for benzhydryl and ferrocenylphenylmethyl pyridinium salts, the Nf value of substituted pyridine decreases in order Nf (4‐ClPy) > Nf (Py) > Nf (4‐MePy) > Nf (4‐OMePy) across in all examined solvents.

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Section: Resultssupporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Solvolytic behavior of some ferrocenylphenylmethyl‐4‐methoxypyridinium cations in various solvents

Jurić

2022

J of Physical Organic Chem

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Impact of the α‐Ferrocenyl Group on the Solvolytic Reactivity – Electrofugality – of Ferrocenylphenylmethyl Cations

et al. 2018

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The electron‐donating effect of the ferrocenyl group in α‐position to the reaction center on SN1 solvolytic reactivity has been quantified by determining the electrofugalities (Ef) of a series of ferrocenyl‐X‐phenylmethyl cations according to the LFER equation: log k = sf(Ef + Nf). Due to highly stabilized transition state, the Ef values are about eight units higher than those of the corresponding benzhydryl cations. Impact of the phenyl group in ferrocenylphenylmethyl derivatives on stabilization of the positive charge is somewhat leveled by the ferrocenyl group, so the rate effect of the substituents on the phenyl ring is suppressed, causing narrow range of Ef parameters and small absolute values of the ρ+ constant. Calculations at B2PLYP‐D3/may‐cc‐pVTZ level of theory showed that the positive charge in ferrocenylphenylmethyl cation is largely shifted from the phenyl to ferrocenyl moiety, and that the substituents on the phenyl ring have small impact on its stability.

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Prediction of the kinetic stability of N‐alkyl‐X‐pyridinium ions in dichloromethane

Matić

Denegri

2021

J of Physical Organic Chem

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Geometries of 20 N‐[4,4′‐bis (dimethylamino)benzhydryl]‐X‐pyridinium ions (DMABh‐X‐pyridinium ions) and of corresponding heterolytic transition structures have been optimized at the M06‐2X/6‐311+G(2d,p) level of theory in the presence of the IEFPCM model with dichloromethane as a solvent. Using the optimized geometries, free energies of activation (∆G‡model) for the model heterolysis of the DMABh‐X‐pyridinium ions in dichloromethane at 20°C have been obtained. A very good correlation between ∆G‡model values for the model heterolysis of five reference DMABh‐X‐pyridinium ions and literature ∆G‡ values for the heterolysis of the same ions in dichloromethane (r = 0.992) validates the procedure for predicting experimental reactivities of the ions (∆G‡calc) in dichloromethane. Accordingly, the correlation has been employed to obtain predicted free energies of activation (∆G‡calc) for heterolyses of other 15 DMABh‐X‐pyridinium ions in dichloromethane from corresponding ∆G‡model values. The high quality of the whole set of the predicted reactivities is confirmed by a very good correlation plot of log kcalc (obtained from ∆G‡calc) versus σ (r = 0.995). Using the previously established correlation equation log k = sf (Ef + Nf), predicted nucleofugality parameters (Nfcalc), which quantitatively describe leaving group abilities, have been determined for various X‐pyridines in dichloromethane, and now can be used not only for comparing leaving group abilities of X‐pyridines with those of other leaving groups on the existing nucleofugality (Nf) scale but also for estimating the reactivity, that is, the kinetic stability, of diverse N‐alkyl‐X‐pyridinium ions in dichloromethane at 20°C.

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Nucleofugalities of Neutral Leaving Groups in 80 % Aqueous Acetonitrile

Cited by 5 publications

References 13 publications

Solvolytic behavior of some ferrocenylphenylmethyl‐4‐methoxypyridinium cations in various solvents

Solvolytic behavior of some ferrocenylphenylmethyl‐4‐methoxypyridinium cations in various solvents

Impact of the α‐Ferrocenyl Group on the Solvolytic Reactivity – Electrofugality – of Ferrocenylphenylmethyl Cations

Prediction of the kinetic stability of N‐alkyl‐X‐pyridinium ions in dichloromethane

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