viii, a, 6 Pratt: Phthalides and Related Compounds 417 



DISCUSSION OF RESULTS 



The substitution of two saturated groups in the ortho position 

 has been shown 1+ to modify the absorption spectrum of benzene 

 by causing several of the narrow bands to coalesce into a well- 

 marked band of considerable persistence. When one or both of 

 the substituting groups contain unsaturated centers possessing 

 residual affinity, the position of the resulting band is modified. 



Thus ortho xylene shows a broad band heading at - =3700, while 



A 



ortho chloraniline gives a similar band at - =3450. 15 



A 



Phthalic acid must be considered as containing two ortho 

 groups possessing little residual affinity. The position of the 

 absorption band corresponds to that of ortho xylene, but the 

 persistence and type are decidedly different. The band cannot, 

 therefore, be attributed to the disubstituted benzene ring alone, 

 but results from the mutual influence of the two carboxyl groups 

 and the ring. The activity of carboxyl is undoubtedly inherent 

 in the doubly bound oxygen with its latent valencies, but the 

 resulting effect is much less than that produced by a true carbonyl 

 grouping. The hydroxyl exerts a counterinfluence that has 

 been demonstrated in many instances and accounted for in a 

 variety of ways. Smedley 16 and others suggest that the carboxyl 

 group may represent a canceling of residual affinities between 

 =CO and —OH, which may be indicated by a structure such 



-C = 



as \ S Although this graphic representation serves to 



OH 

 account for some of the facts in a more or less satisfactory man- 

 ner, it has not as yet received sufficient confirmation for general 

 acceptance. The extra double bond between the oxygen atoms 

 introduces a condition not possible in phthalic anhydride, but 

 the absorption spectrum of this compound indicates no such 

 radical difference in structure. Some such internal compensa- 

 tion is probably taking place, but thus far an insufficient variety 

 of groups causing an analogous result has been studied to permit 

 any definite conclusions being drawn, o-cyanbenzoic, o-chlor- 

 benzoic, 17 and o-sulphobenzoic 18 acids give absorption spectra 

 of the same type as phthalic acid. 



14 Baly and Ewbank, Journ. Chem. Soc. London (1905), 87, 1355. 



16 Baly and Ewbank, loc. cit. 



"Journ. Chem. Soc. London (1909), 95, 231. 



"Scheiber, Ber. d. deutsch. chem. Ges. (1912), 45, 2403. 



" Scheiber und Knothe, Ibid. (1912), 45, 2252. 



