CLASSIFICATION OF CARBON CoSn'ot'NDs. The innumerable compounds that are said to be de rived from benzene all resemble the latter in certain chemical properties—a tact which is in accordance with their formulas having in com mon the benzene ring, or 'benzene nucleus,' con sisting of six carbon atoms. It is therefore con venient to treat the benzene derivatives, other wise called 'a roma t ic compounds,' separately from the rest of the compounds of carbon; and hence the division of organic compounds into fatty (or aliphatic) and aromatic. Just as the aromatic compounds may be considered as de rivatives of benzene, the fatty compounds may be considered as derivatives of methane, or marsh-gas, the simplest of the compounds of carbon; and while the aromatie compounds are characterized by having. in their formulas. a nucleus of carbon atoms arranged in a ring, or closcd chain, the fatty compounds have graphical formulas in which the carbon atoms are arranged along straight lines, or open chains. However, in spite of this constitutional distinction between fatty and aromatic compounds. it must be re membered that the compounds of the two classes are more or less closely related. and that com pounds of one of these classes may, by suitable methods, be transformed into compounds of the other class. A classical example of such a trans formation is 13erthelot's celebrated synthesis of benzene itself from acetylene, effected by simply passing the latter through red-hot tubes. Again,
the subdivisions of the two great classes present a parallelism. Thus, corresponding to the fatly acids, alcohols, aldehydes, ketones. etc.. there are a Ism aromatic acids, alcohols, a Idehydes, ketones. etc.
Just es the division of Organic eomponnds into fatty and aromatic is based on a difference in their chemical constitution, so is the further classification of the compounds belonging to each of the two great classes based on constitutional similarities and dissimilarities.
The most importent classes of carbon com pounds, as well as a large number of individual compounds that are interesting because of the important ride that they play in the bodies of animals and plants, or because of their useful applications in medicine and the arts, are de serihed under their special See HYDRO CAIMON S ; ALCOHOLS ; ETHERS; ALDEII YDES ; KE TONES; AcIDS ; ESTERS; inEs ; AMINES ; HWANo-MET A 1.1.1C COM ro N ; CARBMIYDRATES ; PHENoLs DI A7.0-CoMPOF NDs Resides the derivatives of methane and of benzene. the deriva tives of naphthalene, anth•acene, pyridine, and guillotine (t.v.) deserve mention here. For history and bibliography of Organic chemistry, See CHEMISTRY.