Organic Chemistry is the chemistry of the compounds of carbon. Although the fundamental laws and theories of chemistry are as applicable to these compounds as to all others, there are several reasons for their separate treatment.
In the first place, the number of compounds that contain carbon is extraordinarily large. The only other elements that enter into the composition of any very large number of substances are hydrogen and oxygen. Hydrogen and oxygen are also quite usually associated with carbon in organic compounds. This association, however, is of such nature that carbon is the dominant element. The sheer number of compounds that constitute carbon itself is a sufficient ground for making it a separate branch altogether.
There are certain general characteristics which distinguish the organic substances from the inorganic. Most of the compounds of carbon are decomposed at temperatures which are below a red heat, while many inorganic compounds withstand much higher temperatures and organic compounds are more liable to change when exposed to the light and air than are the inorganic.
The majority of organic substances are practically insoluble in water, which is the solvent of so many inorganic compounds, and are usually soluble in liquids such as ether, chloroform, alcohol, carbon disulphide, and benzene in which few of the inorganic compounds dissolve.
A complete discussion of the compounds of carbon would include carbon monoxide, carbon dioxide, carbon disulphide, certain carbides, carbonic acid and the carbonates – substances which are usually, treated in inorganic chemistry on account of their close relations to inorganic compounds.
All of these compounds, however, have also certain relations, to other compounds of carbon, so that some reference to them which will bring out this relation should be made in organic chemistry.
Sources of organic compounds: Carbon combines directly with hydrogen at high temperatures, and the hydrocarbons which are formed may be employed as the starting point for the preparation of a great variety of other organic compounds. Some simple organic substances may be made by the use of the oxides of carbon, its sulphide, chloride and one or two carbides of the metals, and these may then be built up into more complex compounds by laboratory methods. But in actual practice the chief sources of organic compounds are in the products elaborated in plants and animals.
These substances were the first to receive the name “organic”, and for a long time it was believed impossible to produce any of them artificially from the elements or from inorganic compounds.
Among the important organic compounds which are found already formed in plants are starch, cellulose, sugars, acids or salts of acids, such as oxalic, citric, tartaric acids, the alkoliods, such as quinine and strychnine and many other substances of greater or less complexity.
Petroleum contains many compounds of carbon and hydrogen. Many organic substances are also produced by the destructive distillation of coal, wood and bones – those which are contained in the coal tar being of the greatest interest and practical value.
Furthermore, fermentative processes produce ordinary alcohol from sugar, acetic acid from alcohol and a number of other compounds.
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