Trimethylsulfonium cation

Calculate the energy of proton transfer from trimethylsulfoxonium cation to its ylide, relative to that for trimethylsulfonium cation to its ylide, i.e. 

The formation of a further single bond between sulfur and carbon, as in the trimethylsulfonium cation, may be pictured as involving a 3sp3 unshared pair orbital on sulfur and an empty 2sp3 orbital on carbon in a methyl cation. Thus the three a bonds and the remaining unshared pair (in a 3sp3 orbital) in a trialkylsulfonium ion are distributed approximately tetrahedrally, i.e. the ion is pyramidal, with the sulfur atom at the apex (2). 

Here, both the starting material and the ylide contain hexavalent sulfur. The pA g of the starting material, the trimethylsulfoxonium cation (Me3S" 0), is about 18.2 and is expected to be lower than that of the trimethylsulfonium cation (Me3S+). Dimethylsulfoxonium methylide is thus more stable as well as a softer nucleophile than dimethylsulfonium methylide. Qualitatively, however, the two ylides react in a similar way. The most prominent difference... 

Sulfur ( S)(I= 3j2). S NMR chemical shifts were calculated by the scaled DFT and EMPI approaches for the fluoride, chloride and bromide of trimethylsulfonium ion and S-methyltetrahydrothiophenium ion, in addition to the free cations. and S NMR chemical shifts of sulfur dioxide (SO2) were measured for the range of density (0.05-0.3 mol L ) in the gas phase at 300 and 333 K The chemical shifts for both nuclei are linearly dependent on density showing an increase of magnetic shielding and a decrease of S shielding due to intermolecular interactions. ... 

Trimethylsulfonium iodide undergoes ylid formation by reaction with 50% aqueous sodium hydroxide in the presence of catalytic tetrabutylammonium iodide [16]. The ylid thus formed reacts with aldehydes and ketones to form the corresponding epoxides (Eq. 14.7). The yields with aldehydes are considerably better than those with ketones. The fact that the reaction is slow (48 hours) may be due to the iodide of the catalyst. On the other hand, lauryldimethylsulfonium chloride undergoes reaction with ketones and aldehydes to yield epoxides under alkaline phase transfer conditions considerably more rapidly (6—10 hours). The enhanced rate of this methylene transfer reaction is probably due to the greater organic solubility of the lauryldimethylsulfonium cation [17]. Catalyst poisoning is observed with lauryldimethylsulfonium iodide. Similar reactions have been conducted under ion pair extraction conditions [18]. 

Cations EMI-l-ethyl-3-methylimidazolium, TMS-trimethylsulfonium, TES-triethylsulfonium, TMP-tetramethylphosphonium, TMPA-trimethylphenylammonlum, MPP-n-methyl,n-propylpyrrolidinium. 

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