Geometrical dependence of .gamma.-trimethylsilyl groups on norbornyl solvolyses

The specific solvolysis rates of 2-chloro-2-(methylthio)acetone (3) at 25.0 o C, and 2-chloro-2-(4-methoxyphenylthio)-acetophenone (4) at 50.0 o C have been measured in more than 34 aqueous solvent mixtures including aqueous 2,2,2-trifluoroethanol (TFE), for 4, and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), and in TFE-ethanol. The kinetic solvent isotope effect in methanol and solvolysis rate ratios, at identical ionizing power in 40 (v/v)% ethanol/water compared with 97 (w/w)% TFE/water have been determined. Additional data were also obtained for solvolyses of other substrates related to this work. The investigation of structural effects, caused by the existence of neighboring sulfur-containing and carbonyl (C=O) groups, on the solvolytic reactivity and/or mechanism and the possibility for the stabilization of the solvolytic TS by the developing mesomeric cation, due to the role of the PhS-group, have been attempted using various Grunwald-Winstein (GW) parameter treatments. Regardless of -COPh or -COCH 3 neighboring groups as neighboring group, the solvolytic reactions for both 3 and 4 were evaluated as reactions primarily influenced by the sulfur atom of the -SR group as the activator to make the positive polar TS. In particular, the solvolytic reactions of 4, having an electron donating p-OCH3 substituent, were indicative of the possibility of an ionization pathway with development of a mesomeric cation, stabilised by the sulfur atom and its attached group.

Section: 17mentioning

confidence: 99%

Section: 17mentioning

confidence: 99%

Evaluation of Methylthio and Phenylthio Group Effects in the Solvolyses of 2-Chloro-2-(methylthio)acetone and 2-Chloro-2-(phenylthio)acetophenone Using Extended Grunwald-Winstein Equations

Ryu

Bentley²

2008

“…Initially, simple G-W equation (eq. 1) 2 contains only solvent ionizing power term, 3 that is, only substrates of the unimolecular pathway (S N 1 and E1) are analyzed well, but there are many substrates showed the deviated plots. The reason is the simple G-W equation involves only electrophilic characters of solvents.…”

Section: Introductionmentioning

confidence: 99%

“…The m and l are the sensitivities toward solvent ionizing power (Y) 3 and nucleophilicity (N T ). 5 Many researchers made an efforts to develop the standard substrates of solvent ionizing power and nucleophilicity hardly.…”

Section: Introductionmentioning

confidence: 99%

Kinetic and Theoretical Consideration of 3,4- and 3,5-Dimethoxybenzoyl Chlorides Solvolyses

Park

Kevill²

2013

The solvolysis rate constants of 3,4-(1) and 3,5-dimethoxybenzoyl (2) chlorides were measured in various pure and binary solvents at 25.0 o C, and studied by application of the extended Grunwald-Winstein (G-W) equation, kinetic solvent isotope effect in methanolysis and activation parameters. The solvolysis of 1 was interpreted as the unimolecular pathway due to a predominant resonance effect from para-methoxy substituent like 4-methoxybenzoyl chloride (3), while that of 2 was evaluated as the dual mechanism, with unimolecular or bimolecular reaction pathway according to the character of solvent systems (high electrophilic/nucleophilic) chosen, caused by the inductive effect by two meta-methoxy substituents, no resonance one. In the solvolyses of 1 and 2 with two -OCH 3 groups, the resonance effect of para-methoxy substituent is more important to decide the mechanism than the inductive effect with other corresponding evidences.

“…Correlations with single parameters for polarity (E T ), 1a ionizing power (Y), 2 or nucleophilicity (N) 3 may be used. However, multiparameter equations are often required, e.g., involving Y, N and an aromatic ring parameter (I).…”

Section: Introductionmentioning

confidence: 99%

Stoichiometric Solvent Effect on S_N1 Solvolytic Reactivity Accounting for Phenomenon of Maximum Rates in Methanol-Nitromethane Mixtures

2004

Pseudo-first order rate constants (k obs ) are reported for the following solvolyses in approximately isodielectric mixtures: 3-and 4-methoxybenzyl chloride, bromo-and chlorodiphenylmethane, and 4-chloro-, 4,4'-dichloroand 4-methyl-chlorodiphenylmethane in 0-80% v/v nitromethane-methanol mixtures; and bromo-and chlorodiphenylmethane and 4-methyl-chlorodiphenylmethane in various acetonitrile-methanol mixtures (in the range 0-50% v/v) at 25 ºC. These data, and literature data for t-butyl halides (Cl, Br, and I), and for p-methoxybenzoyl chloride, show rate maxima in solvent compositions of ca. 30% aprotic cosolvent, explained by a stoichiometric solvent effect on electrophilic solvation. Linear relationships are observed between (k obs )/ [MeOH] 2 and [AP]/[MeOH], where [AP] refers to the molar concentration of aprotic cosolvent. The results are consistent with competing third order contributions to kobs, kMM [MeOH] 2 with hydrogen-bonded methanol as electrophile, and kMAP [MeOH][AP] with hydrogen-bonding disrupted by the aprotic solvent.