654 



SCIENCE PROGRESS 



The ring of this gold-yellow substance is therefore composed of 

 four chromophoric groups, viz. two ethylene linkages and two 

 carbonyl groups. The presence of the —CO groups alone is 

 insufficient to produce colour, as may be seen from the similarly 

 constituted but colourless diketo hexamethylene. 



CO 

 / \ 



H,C 



CH„ 



H 2 C CH2 



\ / 

 CO 



It will be observed that although ortho-qumone can also be 



readily formulated, it is an impossibility to construct a similar 



formula for meta-quinone owing to the distribution of the double 



bonds. All compounds derived from quinone, whether by 



substitution of hydrogen by monovalent radicles or of oxygen by 



divalent radicles, are also coloured and are termed quinonoids or 



said to possess a quinonoid structure. This applies only as 



long as they contain the skeleton nucleus. 



or 



/V* 



^ 



Among the more important oxygen substituents may be 

 mentioned derivatives of = CH 2 , i.e. compounds like the well- 

 known dye aurin which are derived from the hypothetical quino- 

 methane = C 6 H 6 =CH 2 . Either or both of the oxygen atoms 

 may also be replaced by nitrogen as in quinone diphenylimide 

 and allied substances. The former is brown-red in colour. 



C 6 H S -N = 



N - C„H 5 . 



A number of polycyclic colouring-matters and dye-stuffs 

 contain the same nucleus and are now formulated in a similar 

 manner as or/Ao-quinones. To this class belong the derivatives 

 of acridine and apo-safranin : 



N N 



nh U^aJ 



N 



Acridine. 



C 6 H CI 



Apo-safranin. 



