286 CONSIDERATION OF CARBON COMPOUNDS. 



39. CONSTITUTION, DECOMPOSITION, AND CLASSIFICATION 

 OF ORGANIC COMPOUNDS. 



Radicals or residues. The nature of a radical or residue has 

 been stated already in Chapter 8, but the important part played by 

 radicals in organic compounds renders it necessary to consider them 

 more fully. 



A radical is an unsaturated group of atoms obtained by removal 

 of one or more atoms from a saturated compound. It is not neces- 

 sary that this removal of atoms should be practically accomplished in 

 order to call a group of atoms a radical, but it is sufficient to prove 

 that the unsaturated group of atoms exists as such in a number of 

 compounds, and that it can be transferred from one compound into 

 another without suffering decomposition. 



Kadicals exist in organic and inorganic compounds ; an inorganic 

 radical spoken of heretofore is the water residue or hydroxyl, OH, 

 obtained by removal of one atom of hydrogen from one molecule of 

 water. Hydroxyl does not exist in the separate state, but it exists in 

 hydrogen dioxide, H 2 O 2 , or HO OH, and is also a constituent of the 

 various hydroxides, as, for instance, of KOH, Ca(OH) 2 , Fe 2 (OH) 6 , etc. 



If one atom of hydrogen be removed from the saturated hydro- 

 carbon methane, CH 4 , the univalent residue methyl, CH 3 , is left, 

 which is capable of combining with univalent elements, as in methyl 

 chloride, CH 3 C1, or, with univalent residues, as in methyl hydroxide, 

 CH 3 OH. 



If two atoms of hydrogen be removed from CH 4 , the bivalent resi- 

 due methylene, CH 2 , is left, capable of forming the compounds 

 CH 2 C1 2 , CH 2 (OH) 2 , etc. 



If three atoms of hydrogen be removed from CH 4 , the trivalent 

 residue CH is left, capable of combining with three atoms of univa- 

 lent elements, as in CHC1 3 , or with another trivalent radical, etc. 



Chains. The expression, chain, designates a series of multivalent 

 atoms (generally, but not necessarily, of the same element), held 

 together in such a manner that affinities are left unsaturated. For 



instance : 



O O 0-0-0 O 0-O-0-, 



are oxygen chains, each one of which has two free affinities which 

 may be saturated, for instance, with the following results : 



H O O H, H O O 0-C1, H-O 00-0 Cl, 



Hydrogen peroxide. Chloric acid. Perchloric acid. 



