SPACE-ISOMERISM 81 



clear when actual models are built up in which the tetrahedral 

 arrangement of the carbon affinities is retained. 



The explosive nature of acetylene derivatives appears to 

 bear some relation to the space formula for carbon, as can 

 be seen by the following space formula for acetylene : — 



C 



A 

 v 



There is evidently a condition of strain between the two carbon 

 atoms, the Hne of attraction not being direct between carbon 

 and carbon as in the case, e.g., of a saturated compound, the 

 space formula for ethane being — 



xl/ 

 C 



C 



Moreover, when a series of carbon atoms is thus joined into 

 a ring, it is found that a differing amount of strain is put upon 

 the bonds, considered for the moment as semi-rigid links, 

 according as the ring contains a different number of carbon 

 atoms. Thus the pentamethylene ring, which may be shortly 

 written thus — 



HgC — CHo 



I 1 " 

 HgC CHg 



\/ 

 CH, 



