140 SCIENCE PROGRESS. 



R'" 

 R'CR" 



R iv CR v 



R vi 



in which R' is over R iv , R" over R v and R"' over R vi . This 

 plane formula may be considered as a projection of the 

 model in which the front groups R'" and R V1 are turned up- 

 wards and downwards respectively. " These projections 

 may be used for illustrating the possible isomers. That 

 there will be four of these will be at once evident, since 

 each asymmetric carbon atom involves a doubling. These 

 differences are represented by changing the order of the 

 groups R'R'R '. But if, without changing the order, we 

 simply move R' to R", R" to R ', R'" to R 1V , we only bring 

 about the above-mentioned rotation, and no isomerism 

 results. But if R' and R" change places we get a new 

 isomer, also by transposing R 1V and R v ; hence the following 

 symbols represent the four isomers. It is plain that these 

 are reduced to two directly the asymmetry of one of the 

 carbon atoms ceases, through R v and R 1V becoming identical."' 



(Van't Hon, /. c, p. 37). 



With three carbon atoms another doubling results, and 

 there should be eight isomers, of which the formulae may 

 readily be constructed. And in general, for 11 carbons there 

 should be 211 isomers. 



As to the character of the isomers, the formulae show 

 that they must occur in pairs, thus No. 1 and No. 4, No. 2 

 and No. 3, in the above series are enantiomorphous and 

 alike in chemical properties, and in all physical properties 

 except those which depend on their enantiomorphism ; but 

 each of the two pairs will differ from the other in activity, 

 melting-point, solubility, etc. 



In confirmation of the theory may be cited borneol and 



