Dimethyl ether hydrogen bonding

The oxygen in an alcohol, such as ethanol, is bonded to one carbon atom and one hydrogen atom. The oxygen in an ether, such as dimethyl ether, is bonded to two carbon atoms. Because of this difference, alcohols and ethers of similar molecular mass have vastly different physical properties. 

Bertie, J. E., and Falk, M. V., The infrared spectrum of the hydrogen-bonded molecule dimethyl ether — hydrogen chloride in the gas phase. Can. J. Chem. 51, 1713-1720 (1973). 

J. E. Bertie and M. V. Falk, Can. ]. Chan., 51, 1713 (1973). The Infrared Spectrum of the Hydrogen-Bonded Molecule Dimethyl Ether-Hydrogen Chloride in the Gas Phase. 

C2HgO, but the atoms in each compound are coimected differently. The oxygen in ethanol is bonded to a carbon and to a hydrogen, whereas the oxygen in dimethyl ether is bonded to two carbons. 

Entries 11 and 13 in Table 3.4 present data relating the efiect of methyl substitution on methanol and methylamine. The data show an increased response to methyl substitution. While the propane barrier is 3.4 kcal/mol (compared to 2.88 in ethane), the dimethylamine barrier is 3.6kcal/mol (compared to 1.98 in methylamine) and in dimethyl ether it is 2.7 kcal/mol (compared to 1.07 in methanol). Thus, while methyl-hydrogen eclipsing raised the propane barrier by 0.5 kcal/mol, the increase for both dimethylamine and dimethyl ether is 1.6 kcal/mol. This increase in the barrier is attributed to greater van der Waals repulsions resulting from the shorter C—N and C—O bonds, relative to the C—C bond. 

Isotope labeling by derivative formation with deuterated reagents is useful for the preparation of analogs such as dg-acetonides, da-acetates, da-methyl ethers, dg-methyl esters, etc. The required reagents are either commercially available or can be easily prepared. (The preparation of da-methyl iodide is described in section IX-F. Various procedures are reported in the literature for the preparation of dg-acetone, da-diazometh-ane57.i63.i73 and da-acetyl chloride. ) These reactions can be carried out under the usual conditions and they need no further discussion. A convenient procedure has been reported for the da-methylation of sterically hindered or hydrogen bonded phenolic hydroxyl functions by using da-methyl iodide and sodium hydroxide in dimethyl sulfoxide solution. This procedure should be equally applicable to the preparation of estradiol da-methyl ether derivatives. 

Hydrogen bonding accounts for the much higher boiling point (78.5 °C) of ethanol than that of dimethyl ether (-24.9 °C). 

Note that for acetic acid there is a hydrogen attached to an oxygen atom (a prerequisite for H bonding) but that for dimethyl ether there is no H atom connected to an F, O, or N atom. 

Explanation Water is a polar substance with strong intermolecular hydrogen bonds. Dimethyl ether is a polar material with weaker intermolecular forces (dipole-dipole). It will... 

The first compound (dimethyl ether) is polar, but not as soluble in water as the second compound (ethanol) which is capable of hydrogen bonding to water. 

McMahon and Kebarle (1986) studied (MeF)2H as a model for (HF)2H . They thought this to be reasonable because the hydrogen bond of a proton bound to two methanols or dimethyl ethers, e.g. [MejO - H OMe2], gives cations with very similar energies to that of the hydrated oxonium ion [H2O H OHj] (Grimsrud and Kebarle, 1973 Meot-Ner, 1984). 

The kinetic and activation parameters for the decomposition of dimethylphenylsilyl hydrotrioxide involve large negative activation entropies, a significant substituent effect on the decomposition in ethyl acetate, dependence of the decomposition rate on the solvent polarity (acetone-rfe > methyl acetate > dimethyl ether) and no measurable effect of the radical inhibitor on the rate of decomposition. These features indicate the importance of polar decomposition pathways. Some of the mechanistic possibilities involving solvated dimeric 71 and/or polymeric hydrogen-bonded forms of the hydrotrioxide are shown in Scheme 18. 

Tests of the best hydrogen bonding agents in ether-alcohol showed the following compds trimethyl-, trimethallyl-, tributyl phosphates, isophorone, dimethyl acetamide, and dibutyl tartrate were superior to dibutyl phthalate or triacetin in the amts reqd for gelatinization and in the viscosities of the resulting solns... 

Cellulose may be converted from a water-insoluble polymer to a water-soluble polymer by the partial etherification of some of the hydroxyl groups by dimethyl sulfate. When the degree of substitution (DS) is 1.5 to 2.0, the hydrogen bonds are sufficiently weakened, and the methylcellulose is soluble in water. Carboxymethyl ethers, such as carboxymethylcellulose (CMC), are also water-soluble. The degree of solubility is related to the DS of the polymer and the pH of the solvent. 

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