PRINCIPLES OF STRUCTURE 



47 



of hydrophobic (i.e., water-repelling) groups in the molecule. On the 

 other hand, the latter groups determine the solubility in homopolar 

 liquids (solvents for fatty substances), such as hydrocarbons, carbon 

 tetrachloride, carbon disulphide, ether, chloroform, benzene, olive oil, 

 etc., and for this reason are designated as lipophilic groups. Table VI 

 gives a survey of the various hydrophilic and lipophilic groups 



TABLE VI 

 HYDROPHILIC AND HYDROPHOBIC GROUPS 



occurring in the organic compounds participating in the construction 

 of the protoplasm. With the aid of this table it is possible in many 

 cases to derive from the chemical structural formula of a substance 

 its solubility in an organic compound. 



Surface films. The lipophilic nature of the alkyl radicals explains the 

 lowering of the surface tension reproduced in Table V (p. 43). As 

 shown in Fig. 41a, the lipophilic ends of the alcohol molecules pro- 

 trude to a certain extent from the hydration layer. In their attempt to 

 escape from the water dipoles, they tend to approach each other and 

 to accumulate at a phase boundary. It is the hydrophobic nature of 

 the alcohol molecules, therefore, which causes their accumulation at 

 the surface; they are said to be surface-active. This applies, of course,. 



