Dimethylether properties

When two different compounds have the same molecular formula but differ in the nature or sequence of bonding, they are called constitutional isomers. For example, ethanol and dimethylether have same molecular formula, C2HgO, but they differ in the sequence of bonding. Similarly, butane and isobutane are two constitutional isomers. Constitutional isomers generally have different physical and chemical properties. 

At this point in our discussion about chemical bonds and structural formulas, we should stress that structural isomers may exhibit very different properties and reactivities. For example, the rates of hydrolysis (reaction with water, see Chapter 13) of the four butyl chlorides shown in Fig. 2.1 are quite different. While the hydrolytic half-life (time required for the concentration to drop by a factor of 2) of the first and third compound is about 1 year at 25°C, it is approximately 1 month for the second compound, and only 30 seconds for the fourth compound. When we compare the two possible structural isomers with the molecular formula C2H60, we can again find distinct differences in that the well-known ethanol (CH3CH2OH) is a liquid at ambient conditions while dimethylether (CH3OCH3) is a gas. These examples should remind us that differences in the arrangement of a single collection of atoms may mean very different environmental behavior thus we must learn what it is about compound structure that dictates such differences. 

Figure 15. Reproduction of certain of the sets of equations and tables constructed by Kopp (1842) in his study of the additive properties of vanous series of molecules. The upper table relates to specific volumes and the tower table to boiling points. In each case the properties of 1 1 mixtures are presented. Here A is acetic acid, B formic add, C benzoic add, a water, diethylether, and 7 dimethylether.

Moreover, all the symmetry elements intersect at a single point (e.g. the oxygen atom in dimethylether (6-1), the nitrogen atom in ammonia (6-7), the middle of the carbon-carbon bond in ethylene (6-5)). The expression paint-group symmetry is therefore used. For each molecule, there is a corresponding point group that completely characterizes its symmetry properties. 

Structure 1 is ethanol and structure 2 is dimethylether. The properties of the two compounds are quite different. For example, ethanol is a liquid at room temperature with a boiling temperature of 352 K, whereas dimethylether is a gas at room temperature and its boiling point is 249 K. 

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