3 Dimensional Structure Of Methane

Methane and Its Iii-Dimensional Structure

Methane, the simplest hydrocarbon, is a gas of molecular formula CH₄, which occurs naturally in underground pockets in the petroleum-producing areas of the world. Colorless and odorless (the odor associated with natural gas in our homes is caused by the deliberate add-on of traces of organic sulfur compounds), methane is an ultimate production of the decay of organic affair in the absence of air. It rises in bubbling from beneath the surface of swamps and marshes, hence its name "marsh gas." Since it burns cleanly and with the release of a nifty deal of heat (Fig. one-1), information technology is ane of the all-time and least polluting of all our common sources of energy.

Figure 1-ane. The combustion of methane is one of the principal sources of energy in modern civilization. The combustion of 16 g of methyl hydride (ane mole) releases 213,000 cal of estrus, enough to enhance the temperature of 2.thirteen liters of water from 0 to 100°C.

Despite the ease with which it burns, marsh gas is, past the standards of organic chemistry, unreactive. Past this we hateful that at ordinary temperatures marsh gas combines merely slowly or non at all with most chemical reagents. For case, it tin can be bubbled unchanged through full-bodied acid or base of operations and heated without effect with most oxidizing and reducing agents. Because the carbon in methane is combined with the maximum number of hydrogens possible, four, we say that it is a saturated hydrocarbon.

Under sufficiently vigorous conditions, for instance, in the heat of a match, saturated hydrocarbons volition react. One of their most useful reactions is with the halogens, especially chlorine or bromine. If a sample of methane is mixed with chlorine gas, no reaction occurs, simply in the presence of sunlight a reaction does take place and a mixture of organic compounds results (Fig. one-two). Gaseous hydrogen chloride is also formed.

Figure one-2. Methyl hydride reacts with chlorine in sunlight to form a mixture of chloro-, dichloro-, trichloro-, and tetrachloromethanes. Only i compound of each formula is known.

The diverse products of the reaction all have different boiling points (b.p.) and may be readily separated from i another and identified. As their molecular formulas bespeak, the products obviously correspond to compounds in which successively one, two, three, and iv hydrogen atoms of methane are replaced by chlorine atoms. These compounds may be named chloromethane (or, alternatively, methyl chloride), dichloromethane (or methylene chloride), trichloromethane (chloroform), and tetrachloromethane (or carbon tetrachloride). It is important to note that all of these products, as well as methane itself, have four bonds to the carbon atom. This tetravalence of carbon is characteristic of well-nigh all of its compounds. We shall meet in the next department how the valences of the smaller atoms, including carbon, tin can hands be predicted from the electronic theory of bonding.

Adjacent, consider the implications for the structure of methane that only one compound of each construction exists, that is, one methyl chloride, one methylene chloride, and so on. For example, the simplest caption for the fact that merely one molecule CH_threeCl exists is that hydrogens in CH₃, are equivalent, and then that no matter which is replaced past chlorine, the same molecule results. Such would exist the case, for instance, if marsh gas were square (Fig. 1-3); just other possibilities be, such equally the tetrahedral model too shown in Fig. 1-3.

Figure 1-3. Ii possible structures for methane and chloromethane which correctly predict that only i compound of the formula CH_iiiCl should be. In the square model all four bonds from carbon are in the same plane (that of the page). In the tetrahedral model, the solid lines indicate bonds in the plane of the folio, the dotted line, behind the page, and the heavy line, in front.

Although both square and tetrahedral spatial formulas predict merely one chloromethane, the square system predicts that two dichloromethanes, CH_iiCl_two, should exist (Fig. 1-4). In one of these molecules the two chlorine atoms would be adjacent to each other, and in the other they would exist on opposite sides of the carbon atom. Note that the distance between the two chlorine atoms would differ for these two compounds. The tetrahedral model, on the other hand, correctly predicts the beingness of simply a single dichloromethane. Some practice may be required until this tin exist conspicuously recognized. All aspects of the sterochemistry (isomerism due to spatial system of atoms) of organic molecules may be explained simply if information technology is causeless that whenever a carbon atom is surrounded past four atoms, these atoms are tetrahedrally arranged. This decision, first reached on strictly organic chemical grounds in 1874, has been fully confirmed past more contempo physical methods.

Effigy i-four. (a.) If methane were square planar, two dichloromethanes, should be.

(b.)The tetrahedral structure correctly predicts the existence of merely ane molecule with the formula CH₂Cl_ii.