Dimethyl ether, electrostatic

Digitoxigenin, structure of, 1097 Digitoxin, structure of, 989 Dihalide, alkynes from, 261 Dihedral angle, 94 Diiodomelhane. Simmons-Smith reaction with, 228-229 Diisobutylaluminum hydride, reaction with esters, 812 structure of, 699 Diisopropylamine, pK.d of, 923 1,3-Diketone, pfCa of, 852 Dimethyl disulfide, bond angles in, 20 structure of, 20 Dimethyl ether, electrostatic... 

Thermodynamic information can also be obtained from simulations. Currently we are measuring the differences in chemical potential of various small molecules in dimethylimidazolium chloride. This involves gradually transforming one molecule into another and is a computationally intensive process. One preliminary result is that the difference in chemical potential of propane and dimethyl ether is about 17.5 kj/mol. These molecules are similar in size, but differ in their polarity. Not surprisingly, the polar ether is stabilized relative to the non-polar propane in the presence of the ionic liquid. One can also investigate the local arrangement of the ions around the solute and the contribution of different parts of the interaction to the energy. Thus, while both molecules have a favorable Lennard-Jones interaction with the cation, the main electrostatic interaction is that between the chloride ion and the ether molecule. 

Active Figure 2.5 The reaction of boron trifluoride, a Lewis acid, with dimethyl ether, a Lewis base. The Lewis acid accepts a pair of electrons, and the Lewis base donates a pair of nonbonding electrons. Note how the movement of electrons from the Lewis base to the Lewis acid is indicated by a curved arrow. Note also how, in electrostatic potential maps, the boron becomes more negative (red) after reaction because it has gained electrons and the oxygen atom becomes more positive (blue) because it has donated electrons. Sign in atwww. thomsonedu.com to see a simulation based on this figure and to take a short quiz. 

The electrostatic potential surface for trimethylamine results from a single non-bonded valence molecular orbital (the HOMO), while the electrostatic potential surfaces for dimethyl ether and methyl fluoride result from a combination of two and three high-lying non-bonded molecular orbitals, respectively, i.e. 

One source of the failure has to do with the fact that the electrostatic potential does not take the energy of electron redistribution (the polarization energy) into account. This is likely to be more significant for trimethylamine (most polarizable) than for dimethyl ether, than for methyl fluoride (least polarizable). The problem can be addressed by explicitly taking the polarization energy into account. 

The polarization potential provides the energy due to electronic reorganization of the molecule as a result of its interaction with a point positive charge. The sum of the electrostatic and polarization potentials provides a better account of the energy of interaction of a point positive charge than available from the electrostatic potential alone. It properly orders the proton affinities of trimethylamine, dimethyl ether and fluoromethane. 

A carbenoid-type mechanism with free or surface-bound species formed by a elimination from methanol promoted by the strong electrostatic field of zeolites was proposed first.433,456,457 Hydrocarbons then can be formed by the polymerization of methyl carbene, or by the insertion of a surface carbene (8) into a C-O bond453-455,458,459 (Scheme 3.2, route a). If surface methoxyl or methyloxonium species are also present, they may participate in methylation of carbene454,455,460,461 depicted here as a surface ylide (9) (Scheme 3.2, route b). A concerted mechanism with simultaneous a elimination and sp3 insertion into methanol or dimethyl ether was also suggested 433,454,457... 

The movement of electrons in Lewis acid-base reactions can be seen clearly with electrostatic potential maps. In the reaction of boron trifluoride with dimethyl ether, for instance, the ether oxygen atom becomes more positive and the boron becomes more negative as electron density is transferred and the B-0 bond forms (Figure 2.6). 

Use SpartanView to examine electrostatic potential maps of trifluoroacetic acid, 3-chloropropene, ter -butyl cation, and protonated dimethyl ether. Assuming that the most positive atom is also the most electrophilic, identify the most electrophilic atom in each molecule. (Identity the most electrophilic carbon atom in 3-chloropropene.)... 

ETHYLENE DIMETHYL ETHER (110-71-4) Forms explosive mixture with air (flash point 29°F/—2°C). Violent reaction with strong oxidizers, lithium tetrahydroaluminate. Incompatible with sulfuric acid, isocyanates. May be able to form unstable peroxides upon standing. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

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