Structure of Simpler Organic Compounds. 63 



the above equation by the two arrows pointing in opposite 

 directions. 



From substances containing two hydroxyl groups, such 

 as that known as ethylene glycol, CH 2 OH CH 2 OH, a 

 dichlor-derivative can be obtained in a similar manner. 

 Halogen derivatives containing two halogen atoms attached 

 to the same carbon atom can be obtained by the action 

 of phosphorus pentachloride on a class of substances 

 known as the aldehydes, the character of which will be 

 discussed later. 



To summarize, the chief methods of preparing the 

 halogen derivatives of hydrocarbons are (a) by the substi- 

 tuting action of halogens (chlorine and bromine) on 

 saturated hydrocarbons, (b) by addition of halogens to 

 unsaturated hydrocarbons, (c) by the action of halogen- 

 ating agents such as the phosphorus halogen compounds 

 on alcohols and aldehydes. 



The following is a list of some of the chief mono- 

 halogen derivatives : 



Methyl chloride, CH 3 C1 Methyl bromide, CH 3 Br Methyl iodide, CH 3 I 



Ethyl chloride, C 2 H 5 C1 Ethyl bromide, C 2 H 5 Br Ethyl iodide, C 2 H 5 I 



Propyl chloride, C 3 H 7 C1 Propyl bromide, C 3 H 7 Br Propyl iodide, C 3 H 7 I 



Butyl chloride, C^Cl Butyl bromide, C 4 H 9 Br Butyl iodide, C 4 HgI 



Amyl chloride, C 5 H n Cl Amyl bromide, C 5 H u Br Amyl iodide, C 6 H n I 



These substances can all be derived from the corresponding 

 alcohols. In the higher members of the series isomerides 

 can exist ; the isomerism depending upon the configuration 

 of the hydrocarbon from which they are derived, and the 

 position in these hydrocarbons in which a hydrogen atom 

 is replaced by a halogen. A word is here necessary as to 

 the nomenclature employed. The alcohols from which 

 they are obtained are methyl alcohol, CH 3 (OH), ethyl 

 alcohol, C 2 H 5 (OH), propyl alcohol, C 3 H 7 (OH), butyl alcohol, 

 C 4 H 9 (OH), and amyl alcohol, C 5 H n (OH). These alcohols 



