420 The Philippine Journal of Science 1913 



is to be noted when the activity of the lactone ring is increased 

 by the introduction of unsaturated centers. Reference to the 

 curves obtained with substituted phthalids of this class clearly 

 shows that in every case an absorption band was found less 

 refrangible than that given by phthalic acid. 



One of the carbonyl groups of phthalic anhydride may be re- 

 placed by two atoms of hydrogen giving phthalide. This re- 

 moves one of the double bonds, and would entirely destroy the 

 absorption band if it were due solely to conjugation between 

 the two carbonyl groups. This is not the case, as phthalide 

 shows well-marked selective absorption (fig. 4), and, moreover, 

 the band retains its characteristic type. It heads between that 

 of phthalic acid and its anhydride, thus showing greater activity 

 than the former and less than the latter. The effect of destroying 

 one of the double bonds joined to the lactone ring does not 

 appear ever to result in eliminating the absorption band, but 

 merely modifies its position or persistence. If conjugation be- 

 tween latent valencies is taking place, it must be between the 

 anhydride oxygen and the remaining carbonyl group. This is 

 rendered improbable by the great similarity between the spectra 

 of phthalic acid and its anhydride. Moreover, other acids con- 

 stituted similarly to phthalic acid, such as phthalylhydroxamic 

 and anilidophthalamic acids in which no anhydride oxygen is 

 present, have been shown to cause a similar absorption band. 21 



The manner in which these latent valencies of a carbonyl 

 group are called into play by near-by atoms or radicals deter- 

 mines the position of the resulting band, its persistence, and the 

 concentration at which it appears. In the case of phthalic an- 

 hydride the two carbonyl groups are in the p position, and 

 conjugation of the a diketone type represented by: 



C=0: C=0 



I or |: i 



C=0: C=0 



does not appear to be the deciding factor. A very marked 

 difference between the absorption spectra of camphorquinone and 

 methylene camphor 22 shows the effect of disturbing such a con- 

 dition, although the double bond is not removed. The substi- 

 tution of methylene with little residual affinity for the active 

 oxygen atom greatly reduces the activity of the entire molecule. 

 The substitution of two hydrogen atoms for the oxygen of 



21 Pratt and Gibbs, This Journal, Sec. A (1913), 8, 165. 



22 Lowry and Southgate, Journ. Chem. Soc. London (1910), 97, 915. 



