454 



lias been lijdrated (2) (fig. 5), and it has quite disappeared in tlie 

 dicycloliexyl ketone (3). That tor the rest the c^yclohexyl nnclens 

 weakens the activity of the phenyl nucleus less than a |)ni'ely 

 alipiiatic group, is proved l)y the much smaller activity of phenyl 

 n. hexyl ketone (4) (fig. 5), which may be put on a line with tiie 

 activity of acetophenon and i)ropiophenon (6,7) (fig. 6). On intro- 

 duction of CjHj-groups into the CH, -group of acetophenon, the 

 activity at first greatly increases (8,9), suddenly becoming in 

 triphenyl acetone. It is, indeed, known that f?-benzpinacoline lacks 

 all the ketone characteristics. In the phenyl substitution products of 

 acetone (quite inactive in themselves, just as <ii-n-liexyl keton (5, 11)), 

 the introduction of only one phenyl group appears to make the 

 compound photo-active (12). Of the higher phenyl substitution pro- 

 ducts, the molecules built symmetrically show the greatest activity 

 (compare 13 and 16 with 14 and 15). 



c. The photo-activity of the «-(i-óï ketones is a much more general 

 property, and bound neither to the specifically aliphatic or aromatic 

 character, nor in pai'ticular to the more or less symmetrical sti'uc- 

 tiire of the molecule. The introduction of a second = group 

 has mostly a greatly strengthening influence on the photo-activity 

 (compare 18 and 20 with 11 and 61, in which possible disturbing 

 influences issuing from the rest of the molecule, are thrown into 

 the liackground. In this connection it is e.g. interesting to point 

 out that phenanthrene qninone (25), which is to be considered as 

 a particularly orthosubstituted benzil, far exceeds all the examined 

 ketones with regard to its relative activity, whereas fluorenon (28), 

 which may be compared with it, is perfectly inactive. The opposite 

 case presents itself in the comparison of benzil (19) with regard to 

 beuzophenon (1), where the di-ketone compared with the mono- 

 ketone is less active. It may, howe\er, be possible that in conse- 

 quence of the slight solubility of benzil in alcohol the maximum 

 activation concentration cannot be reached. 



Of great importance is also the activity of the «-jJ-di-ketones, 

 which carry one or two furane-nuclei (21 and 22), which furnishes 

 a new proof of the great resemblance in properties of the furane 

 and benzol derivatives. 



d. Thus we see that the phenyl and furyl groups do not exert a 

 disturbing influence on each other in the «-/i-di-ketone ; this influence 

 is, however, evidently particularly strong in the corresponding 

 mono-ketone, phenyl furyl ketone (17), which presents a very small 

 activity. Here the above-mentioned influence of the symmetry of 

 the molecule on the photo-activity of the mono-ketone is very 



