548 



SCIENCE PROGRESS 



that benzene consisted of six cells of eight electrons in contact 

 round a ring ; if there is threefold contact between each pair of 

 cells the thirty available electrons are fully utilised, each carbon 

 atom sharing three electrons with those on either side [xii]. 



H 

 H 



H 



•• *C .' 

 C* -c 



c .c 



.* C-. 

 H 



H 

 H 



H 

 H 



C 



• « 



C 



H 

 *C 



'C 

 H 



/C 



•.c:h 



[xii] [xiii] 



Such a structure corresponds to the centric formula for benzene ; 

 the Kekule formula [xiii] consists of three sets of pairs of cells, 

 the cells in one pair having fourfold contact with each other, 

 but only double contact with a cell in a neighbouring pair. 

 This, however, is little more than a restatement of the older 

 formulae in a new nomenclature. Eraser [Trans. Chent. Soc, 

 1922, 121, 188) has put forward an electronic structure for 

 benzene in which duplets, that is, two electrons held in common 

 corresponding to the "bond" of classical organic chemistry, 

 are shared according to the following method [xiv] : 













.^;;^^^o 



-D 





/ / 

 / / 

 / / 

 / / 



[xiv] V — y 



