- Photoelektronen-Spektren und Molekueleigenschaften. CXLVIII. Die niedrigen ersten Ionisierungsenergien β-trimethylsilyl-substituierter Ether RO-CH3-nn und RO-Si3
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The first vertical ionization energies of dialkylethers are lowered up to 3 eV (!) by β-trimethylsilyl substituents and, therefore, further confirm the powerful electron donor effect of -CH3-nn and -Si3 groups.The gas-phase photoelectron spectra are assigned based on geometry-optimized MNDO calculations and the substituent effects are discussed in terms of conformationally dependent hyperconjugative second order perturbations.
- Bock, Hans,Meuret, Jochen
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- Correlation of the specific rates of solvolysis of trimethylsilylmethyl trifluoromethanesulfonate using a two-term Grunwald-Winstein equation
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The specific rates of solvolysis of trimethylsilylmethyl trifluoromethanesulfonate have been measured at 25.0 °C in ethanol, methanol, and 2,2,2-trifluoroethanol (TFE) and their mixtures with water. Determinations were also made in aqueous acetone and in TFE-ethanol mixtures. An extended (two-term) Grunwald-Winstein equation correlation gave sensitivities towards changes in solvent nucleophilicity and solvent ionising power as expected for an SN2 pathway, consistent with a previous proposal. For four solvents specific rates were determined at three or four additional temperatures and appreciably negative entropies of activation were observed, consistent with the proposed mechanism. At -20 °C, the specific rate of methanolysis is almost identical to that for methyl trifluoromethanesulfonate, suggesting a fortuitous balance between steric hindrance effects and a favourable electronic effect upon the introduction of the trimethylsilyl group.
- Kevill, Dennis N.,Goken, Erin G.,Park, Byoung-Chun
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p. 173 - 175
(2007/10/03)
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- Nucleophilic Substitution Reactions of Trimethylsilylmethyl Arenesulfonates with Anilines and Benzylamines in Acetonitrile
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The results of kinetic studies on the reactions of trimethylsilylmethyl arenesulfonates, 1 (Me3SiCH2OSO2C6H4Z), with anilines and benzylamines in acetonitrile at 65.0 deg C are reported.The relatively large positive value of the cross-interaction constant between substituents in the nucleophile (X) and leaving group (Z), ρxz, indicates that the reaction proceeds by a SN2 process with a relatively tight transition state.The enhanced rate of 1 compared with the rates for other corresponding carbon analogues leads us to conclude that the destabilizing effect of the α-silyl group on the ground state of 1 due to geminal interaction is important not only for SN1 but also for SN22 reactivities.
- Oh, Hyuck Keun,Shin, Chul Ho,Lee, Ikchoon
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p. 2411 - 2414
(2007/10/02)
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- MARKED MEDIUM EFFECTS ON THE SUBSTITUTION AND THE ADDITION-REARRANGEMENT-EJECTION REACTIONS OF (HALOMETHYL)SILANES WITH METHOXIDES
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Reactions of methoxides with (halomethyl)silanes at silicon are facilitated by aprotic solvents and cation separation.
- Kreeger, R. L.,Menard, P. R.,Sans, E. A.,Shechter, H.
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p. 1115 - 1118
(2007/10/02)
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- Alcoxymethyltributyletains precurseurs d'alcoxymethyllithiums: application a la synthese de monoethers d'α-glycols et a l'homologation de cetones en aldehydes
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Ethoxymethyltributyltin (obtained from diethoxymethyltributyltin, acetyl chloride and tributyltin hydride) and methoxymethyltributyltin (obtained from chloromethyl-methyl ether and tributylstannylmagnesium chloride) have been transmetallated with butyllithium to give the corresponding alkoxymethyl lithium reagents.This reaction, although usually performed in ether, is possible in a variety of other solvents thus simplifying some of the problems encountered during isolation of the products.The alkoxymethyllithiums obtained react with aldehydes and ketones to give cleanly the corresponding monoprotected α-glycols.Stereochemical trends were observed for hydratropaldehyde and 4-tertiarybutylcyclohexanone, while regiochemical trends were evaluated in the case of cyclohexen-2-one.Syntheis of aldehydes has been achieved in good yields from tertiary monoprotected α-glycols using conventional methods.
- Duchene, Alain,Mouko-Mpegna, David,Quintard, Jean-Paul
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p. 787 - 793
(2007/10/02)
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- Onium Ylide Chemistry. 2. Methylenedialkyloxonium Ylides
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We report evidence for the long sought after methylenedialkyloxonium ylides from methyloxonium ions by two independent routes, proving their intermediate formation through derived product analysis.Reaction of trimethyloxonium salts with sodium hydride results in competing proton abstraction besides methane formation (hydride methylation).Subsequent methylation of the formed methylenedimethyloxonium ylide by excess trimethyloxonum ion is resulting in C1 --> C2 conversion and formation of dimethylethyloxonium ion which with sodium hydride gives ethane (and methane) or by β-elimination ethylene.Besides expected fluoride alkylation products, i.e., alkyl fluorides and fluorosilanes, fluoride-induced desylilation of dimethyl((trimethylsilyl)methyl)oxonium tetrafluoroborate also results in the formation of methylenedimethyloxonium ylide giving via subsequent methylation and cleavage methyl ethyl ether and ethyl fluoride.
- Olah, George A.,Doggweiler, Hans,Felberg, Jeff D.
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p. 2112 - 2116
(2007/10/02)
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- FACILE HYDROGEN/METAL EXCHANGE BETWEEN BUTYLPOTASSIUM AND SATURATED ETHERS
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At temperature between -100 and -40 deg C, lithium salt-free butylpotassium (prepared from dibutylmercury) readily metalates saturated ethers such as dimethyl ether or tetrahydrofuran.
- Lehmann, Ruth,Schlosser, Manfred
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p. 745 - 748
(2007/10/02)
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