THE ABSORPTION SPECTRA OF VARIOUS PHTHALIDES AND 

 RELATED COMPOUNDS 



By David S. Pratt 



(From the Laboratory of Organic Chemistry, Bureau of Science, 

 Manila, P. I.) 



Fifteen text figures 



Phthalic acid is the parent substance from which a large num- 

 ber of condensation products are obtained that have long oc- 

 cupied a prominent position in chemical discussions. The 

 marked change of color exhibited by the phthaleins upon salt 

 formation has given these compounds a prominent position 

 in all theories regarding constitution and color. The rapid pro- 

 gress in spectroscopic investigation and the ever increasing vol- 

 ume of data available concerning the relation between molecular 

 structure and optical activity has resulted in broadening our 

 conceptions of color changes and modifying our ideas of the 

 underlying causes. Before the absorption spectra of complex 

 substances such as the phthaleins can be rationally interpreted, 

 it is essential to have considerable data relative to similarly con- 

 stituted compounds possessing simple structures not subject to 

 molecular rearrangement in the quinoid-benzenoid sense. Many 

 of the phthalids are suitable for the purpose, and therefore form 

 the basis of this investigation. Since many simple phthalids 

 of definite, fixed structure dissolve in concentrated sulphuric 

 acid with the production of color, this solvent was included for 

 comparison with absolute alcohol. 



DESCRIPTION OP THE ABSORPTION SPECTRA 



PHTHALIC ACID 



/COOH 



x COOH 



Phthalic acid in ordinary solvents has been studied by many 

 observers and its absorption spectrum been found to show a 



band heading at - = 3700. The solution in sulphuric acid 



exhibits a very different spectrum. Here two well-marked bands 

 make their appearance (fig. 1). 



That nearer the red heads at - = 3300, and the second in 



A 



the benzene region shows at - = 3800. Both bands exhibit 



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