2698 MORTON AND ROGERS: CCCLXIX.-4bsorption 8pectra and Imtam-Lacttim Tauherism. By RICHARD AIAX MORTON and EDWARD ROQEES. IT was ~bssumed by the earlier workers in absorption spectra that compounds of similar constitution would show similar absorption FIG. 1. FIG. 2. 2400 2800 3200 3600h 2400 2600 2800 3000A 6 m pi 4,000 2,000 0 - CarbostyriE. -- S-Ether. - o-Eydroryca&an$l. .... 0 -Ether. -_ N-Ether. - * - - O-Bhr. curves. Accordingly in order to decide between alternative structures of a substance it was only necessary to compare its absorption spectrum with those of two derivatives of known constitution; if the general shape of its absorption curve was similar to that of a derivative the two substances had analogous structures. In the hands of Hartley and Dobbie (J.1899,75,640) this method of interpreting absorption spectra led to conclusions in the case of lactam-lactim isomerides which are very generally quoted as establishing the value of absorption spectra in orgaaic chemistry. These workers examined isatin carbostyril and o-hydroxycarbanil together with their 0- and N-ethers; in each caSe the absorption spectrum of the parent substance resembled that of the lactam ether ABSOBPTION SPECTBA AND LA~~AM-LACTIM TAUTOMEBISM. 2699 An examination of the published curva shows that the frequencies of maximum absorption a m nearly the same for lactam and l a c k isomerides in all three cases. It is agreed by all present-day workers in the field of abrption spectra that the wave-lengtha of maximum absorption are of great importance in the inimpretation of data.Certain authorities notably Baly and Henri attach fundamental importance to these frequencies aa a basis for the interpretation of absorption spectm in terms of the quantum theory. Accordingly the f a c t thah the shape of curva is not regarded 88 a trustworthy guide to interpretation coupled with the decided advantages enjoyed by present-day workem over the pioneers in respect of tecmque made it seem worth while to repeat the work of Hartley and Dobbie. Isdin was found by Hartley and Dobbie to show two bands. Hick (this vol. p. 774) found four bands. At the time when Hicks’ paper appeared the present work had been completed and only three bands had been found. Subsequent search has not disclosed the fourth band.The three bands are at 4130A. e (max.) 625 ; 2950A., e (max.) 3,900; 2430A. e (max.) 26,000 (for graph see Hicks, loc. cit. p. 771). $-MethyZkztin (N-ether) like the went substance shows three bands at 2465A. 3OOOA. afid 41951. The curve follows that of isatin very closely. MethyZktin (0-ether) examined as soon as possible f i r preparation in the pure state shows three bands at 2447A. 2965A., 4140A. 5-Io&oisatin exists in two forms red and yellow. The red form in alcohol shom two bands 2500 and 4250A. with an inflexion near 3030A. the extinctions being 25,000 510 and 2000 (ca.), respectively. In glacial acetic acid the band at W A . was observed for the red form and an inflexion near 3000& but on account of absorption by the acetic acid the band at 2500A.could not be observed. In a fresh solution of the yellow form there is little selective absorption but after some time the bands due to the red form appear. Hicks records another band for iodoiaatin in the extreme ultra-violet. In neither isatin nor idohtin can we confirm the fourth band. A revieion of the work of Hartley and Dobbie proves disappointing, for the curves are so much alike as to preclude the possibility of deciding questions of structure from them. The absorption spectra of the isomerides are nearly identical. CarbodyriZ shows two ban& at 2690A. and 3270& e (max.) 7000 and 6750 respectively. The N-methyl ether hse bands at 2705& and 3280A. e (max.) 6600 and 6Oo0 respectively. The The curve again follows closely that of isatin curves are almost identical in agreement with the work of Hartley and Dobbie.The 0-methyl and 0-ethyl ethers are almost identical as regards absorption but me quite Werent from either the N-ether or the parent substance 0-Methyl ether 3222 and 3085A. e (max.) at 4500 and 3700 respectively; 0-ethyl ether 3226 and 3085A., e (max.) at 4500 and 3700 respectively. Both 0-ethers show a pronounced inflexion near 2650A. The analogous band in the parent substance and the N-ether has thus ma. 3. 2400 2600 2800 400 300 3 200 1oc any claim to discriminate between the alternative structures for o-hydroxgcarbanil. PWogZucid also has been examined together with its trimethyl ether. Phloroglucinol shows the following results : almost disappeared.The results confirm the wnclu-.&m of Hrtrtley and Dobbie, but the experimental basis is different since the curve for the 0-ether is different from that of these authors. o-Hydroxycurbanil shows one band with its head at 2736A. e (rnax.) 5150. The N-ether shows one band at 2738A. e (max.) 5600 and the 0-ether one at 2735& e (max.) 4700. The curves are not very Merent from those of Hartley and Dobbie. The only difference observed between these substances was in respect of the persist-ence of the bands. Revision of the work leads tn the conclusion that the curves do not warrant Solvent. hmax. emax. Solvent. hmax. emax. Alcohol ............ 2665 A 380 Aqueous metic acid 2660 A 375 Water ............... 2662 370 Alcohol with sodium Glacial acetic acid 2660 375 ethoxide .........2518 15,200 Ditto in excess...... 3472 6,60 TEYPANOCIDAL ACTION AXD ~EMICAL CONSTITUTION. PABT m. 2701 Phloroglucinol trimethyl ether shows one band at 2646& e (m.) The results me therefore in harmony with the aecepted hydroxy-465. structure of phloroglucinol. C d W . In the cwes of isatin and o-hydroxycctrbanil the work of Hartley and Dobbie is unsatisfactory. Revision shows that absorption spectra do not provide any very obvious meam of deciding the In the cases of phloroglucinol and carbostyril repetition of the work does not controvert the conclusions of these authors. It may be asserted $hat in general conclusions based on the shape of absorption curve8 need careful examination before reliance can be placed on them. Absorption spectra measurements should be interpreted by quantitative considerations concerning frequencies of maximum absorption. The present work will be discussed from this point of view at a later date. B b C t U I ' 8 . We wish to express our gratitude to Professor E. C. C. Baly F.R.S., for the interest he has taken in the work. One of us (E. R.) ia indebted to the Department of Scientific and Industrial Research for a maintenance grant. THE UNIVERSITY LIVERPOOL. [Received July 9th 1925.