326 F. B. GUTHRIE. 



1st, both in the same direction as the double bonds (a) 

 2nd, both in the opposite direction (b) 

 3rd, one in the same direction with the double bonds (a) 

 and one in the opposite direction (b). 



Case B. The double bonds travel, one pair in the direction 

 (aa), the second pair in the direction (bb). There are three 

 combinations possible, as in the previous case. 



1st, ;in which both single bonds travel in the same 



direction (a) 

 2nd, in which both single bonds travel in the same 



direction (b) 

 3rd, where the single bonds travel in opposite directions 



(a and b). 



Case 0. One pair of the double bonds travels in the same 

 direction (aa), the second pair travels, one in the direction 

 (a) the other in the direction (b). This also permits of 

 three combinations according to the direction of the single 

 bonds. 



Case D. The individual bonds in each pair of double bonds 

 travel in different directions (ab) (ab). Giving rise as 

 before to three modifications depending on the direction o* 

 the single bonds. 



Out of the twelve figures which it is possible to construct 

 we get only the following figures which are symmetrical. 



(i) 



T. I 



This is Case Al, in which double and single bonds all have 

 the same direction, resulting in a symmetrical stable 

 molecule in which the electric charge is evenly distributed. 



