CARBOHYDRATES 13 1 



In the new class of compounds which we shall consider we 

 shall meet with no new group of derivatives but mention a few 

 which, though of like character, are derived from other hydro- 

 carbons which possess a distinctly new property and constitu- 

 tion. 



All of the compounds thus far considered have been derived 

 from members of the methane or saturated series of hydro- 

 carbons. In this series one of the fundamental ideas in con- 

 nection with them is that of saturation. In methane and all of 

 its derivatives the carbon atoms are always fully satisfied or 

 are saturated, and this is shown by the fact that so far as the 

 carbon atoms are related to each other they are united by only 

 a single linkage and furthermore whenever derivatives are 

 formed it is by a reaction of substitution, never by addition of 

 new elements or groups. Each carbon element has four uni- 

 valent elements or groups attached to it as in ethane, H3C — CH3 

 or ethyl alcohol H3C— CH2(0H) or one bivalent element and 

 two univalent elements or groups as in aldehydes, 



R-C=0 R-C=0 



I and in acids | 



H OH 



or the carbon has a trivalent element and one univalent element 

 or group as in the cyanides R — C=N. In some cases ad- 

 dition does occur due to the conversion of a bivalent oxygen 

 into a univalent hydroxyl, necessitating the addition of a new 

 univalent group as in the addition products of the aldehydes. 



NH2 



R-C = +HNH2 -> R-C -OH 



H H 



Aldehyde Aldehyde ammonia 



But in none of these cases of addition does the change effect 

 the single linkage by which carbons are united to each other. 

 Unlike these saturated hydrocarbons we have other hydro- 



