Methyl ethers molecular structure

Here we have two substances, ethyl alcohol and methyl ether, which have the same molecular formula, C2H5O, and yet quite clearly are different compounds. How can we account for the existence of these two compounds The answer is they differ in molecular structure. Ethyl alcohol has the structure represented by I, and methyl ether the structure represented by II. As we shall see, the differences in physical and chemical properties of these two compounds can readily be accounted for on the basis of the difference in structure. 

Dimethylamino)methyl]-5-methylphenyl]lithium is a white crystalline solid and is pyrophoric in air. Furthermore, it is soluble in hydrocarbons and ethers. Molecular weight determinations in benzene have established a tetrameric structure.12 In THF, like [2-[(dimethylamino)-methyl]phenyl]lithium, this tetramer breaks down to a dimeric species. 

Important as the molecular formula is. it does not describe fully the properties, or even in some cases the identity, of chemical compounds. For example, there are two compounds that have the molecular formula CjFLO. They are different in all their properties, both chemical and physical. This difference is due to a difference in the manner in which the atoms are connected in the molecules of the two substances. These differences can be shown only by the use of structural formulas, such as those shown in Fig. I, in which the valence bonds between the atom are shown. These structural formulas are determined circumstantially, lhat is. by the chemical reactions into which the compounds enter. (However, (heir arrangements have been confirmed In many cases by a direci instrumental means such us speclrometric methods, x-ray studies, etc.) These reactions differ markedly for ethyl alcohol and methyl ether. Such compounds which have the same molecular formula but differ due to the arrangements or positions of their atoms are called isomers, and the type just cited, in which the difference is in the grouping of the atoms, are called functional isomers. These, and many other lypes of isomers, are treated in the entry on Isomerism. 

Maher, George G., The Methyl Ethers of the Aldopentoses and of Rhamnose and Fucose, X, 257-272 Maher, George G., The Methyl Ethers of D-Galactose, X, 273-282 Manners, D. J., The Molecular Structure of Glycogens, XII, 261-298 Marsh, C. A. See Conchie, J. McCloskey, ChesterM., Benzyl Ethers of Sugars, XII, 137-156 McColloch, R. J. See Kertesz, Z. I. McDonald, Emma J., The Polyfructo-... 

Moreover, poly(a-methylolbenzoin methyl ether acrylate) [poly(MBA)] has been checked in the UV induced polymerization of styrene and compared with poly(AB) and other low-molecular-weight structural models such as benzoin, a-methylol benzoin methyl ether (MBE) and a-methylol ben2 in methyl ether acetate (MBAc) [107]. 

Low-molecular-weight structural models for both the series of pol5oneric systems, such as MB Ac and a-ethyloxymethyl benzoin methyl ether (MBEE) have also been prepared and tested in terms of photoinitiation activity [61,84],... 

Figure 3. Structural formulas help differentiate between substances that share identical molecular formulas, such as ethyl alcohol and methyl ether. fHustratiai by Hans Cassidy. Courtesy of Gale Group.

A large number of structurally characterized bis(trimethylsilyl)amido complexes now exist Table 5 gives a representative selection of monometallic homoleptic compounds, both base-free and with coordinated ethers. Other examples are known with coordinated fiuorobenzenes, isonitriles,methylated pyridines, various amines (TMEDA, PMDTA, TMPDA (Tetra-methylpropylenediamine), BzNMe2 (benzyldimethylamine)), Ph PO, (Bu"0)(Pr )C0, and l,3-(Pr )2-3,4,5,6-tetrahydropyrimid-2-ylidene. Their structures illustrate the complex interactions between metal size, ligand bulk, and molecular structure that exist with these metals. For example, among the alkali metal base-free species, the unsolvated Li derivative crystallizes as a cyclic trimer, whereas the Na salt is found both as a trimer " and as infinite chains of [Na-N(SiMe3)2—] units. The potassium, rubidium, and caesium derivatives exist as discrete dimers in the solid state, constructed around planar [M—N-]2 frameworks. 

Catalysts containing niobia supported on various oxides have been the subject of considerable recent interest [1-4]. The molecular structures and reactivity of niobium oxides supported on alumina, titania, zirconia and silica have been intensively investigated over the last few years. Niobia supported on silica has been shown to be active for the dehydrogenation and dehydration of alcohols, photo-oxidation of propene and oxidative decomposition of methyl tertiary butyl ether. Titania supported niobia is active for the selective catalytic reduction (SCR) of NO by NH3. 

This difference in molecular structure gives rise to a difference in properties it is the difference in properties which tells us that we are dealing with different compounds. In some cases, the difference in structure—and hence the difference in properties—is so marked that the isomers are assigned to different chemical families, as, for example, ethyl alcohol and methyl ether. In other cases the difference in structure is sp subtle that it can be described only in terms of three-dimensional models. Other kinds of isomerism fall between these two extremes. 

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