PURVIS THE INFLTJENCE OF DIFFERENT NUCLEI ETC 2771 CCCLXXX1.-The Inpuence of Different Nuclei on the Absorption Spectra of Substances. IN previous papers (J. 1914 105 590 1372) the author described the absorption spectra of substances containing several benzene nuclei and it was shown that the phenomena were very different in substances containing two three and four benzene residues even when the nuclei with which they were combined had no specific absorption. The aim of this communication is to describe the absorption spectra in the ultra-violet region (1) of substances in which each nucleus shows specific absorption when uncombined and (2) of substances in which only one of the nuclei shows specific absorption. Alcoholic solutions of the following substances were examined : Salicylic wid,.phenyl salicylate o-acetoxybenzoic acid benzyl salicylate thymol dicylafe camphor camphor dcylate theo-bromine theobromine salic ylate t heo bromine o- acetoxybenzoate , caffeine caffeine SalicyIate caffeine benzoate caffeine citrate, caffeine hydrochloride phenazone phenazone salicylate quinine, quinine salicylate and quinine o-acetoxybenzoate. Most of the substances were examined in the first instance in M/200-solution, By JOHN EDWARD PURVIS 2772 PURVIS THE INFLUENCE OF DIFFERENT NUCLEI but theobromine and caffeine and their salicylates were soluble only in about &2/2,OOO-&rength. A condensed cadmium spark was the source of radiant energy. Hartley’s observation (J. 1888 53 641) that this substance has two bands in the ultra-violet region has been confirmed.Salicylic acid. FIG. 1. Oscillation jrquencies. 30 32 34 36 38 40 43 44 Upper curve8. Lower czcmrs. I PhenyE salicylatc. I Theobmnine. I1 o-Acetoxybenzoic acid. II Theobmmine ealicyEafte. I11 Camphor ealicylate. III Theobrmine o-acetoxybenzoate, Pirenyl sdicylate. This has two bands like those of the acid. On comparing photographs of the two substances it was clear that there was a shift towards the red end and the less refrangible band of the salt was not so strong as that of the acid; and also the more refrangible band was better marked. Fig. 1 I (upper series) gives the curve for the salt. The replacement of the hydrogen in the hydroxyl group by acetyl has produced a strikurg change in the absorption (Fig.1 11 upper series). The less refrangible ba,nd a t o-Acetoxybenxoic mid ON THE ABSORPTION SPECTRA OF SUBSTANCES. 2773 1/G650 (1,2740) is much weaker and is shifted f0Wr;trds the more refrangible regions. When the spectrum is compared with that of salicylic mid or phenyl salicylafe the more refrangible band is represented by an extension of the rays from 1/A4150 ( M 8 ) to 1/14350 (X2298). The general appearance of the absorption is not unlike that of benzoic acid and this is usually assigned to the benzene nucleus. Thymol salicylate. Benzyl sdicylate. The bands of these two substances were similar to those of salicylic acid and phenyl aalicyl-ate and mered chiefly in position correspondmg to difEerences in their respective molecular weights. The three benzene bands of the benzyl nucleus do not appear as they do in such substances as dibenzyl carbamate and benzyl chloride (Purvis J.1914 105, 1372; 1915 107 496). The curves have not been reproduced. The curve (Fig. 1 III upper series) shows that the two bands of the acid have not been very much affected. The dif€erences are that the less refrangible band is not so strong as that of mlicylic acid or of phenyl salicylate and the more refrangible band is weaker. Camphor has a weak band at 1,h3480 (X2870) aa described by Baly Marsden and Stewart (J. 1906 89, 979) and c o h e d by Hartley (J. 1908,93,961) and by the author (J. 1915 107 643). The&onsine ; theobromi?ie salicybcste ; theobromine o-aceioxybenz-ode. Cafjeine ; cufjeine salicylste. Hartley (J. 1905 87 1796) describes the absorption spectra of theobromine *and caffeine.His photographs show a defhite band in theobromine but not in caffeine. In the text he states that " there is a sudden lengthening of the spectrum and its enfeeblement between 1/X3675 (A2720) and 1/X3794 (A2635) as if an absorption band was indicated hereabouts of a very feeble or ill-defined character." The author has repeated the observations and finds that caffeine has a definite band like that of theobromine but shifted a little more towards the red end. The curves of theobromine and its salts (Fig. 1 I lqwer series) show that the rays passing through theobromine salicylate rapidly step out between 1/h3030 (13298) and 1/~3350 (U980) and there is a band at 1/13650 (X2740). It is obvious from this that the acid nucleus exerts some iduence on the absorption.The curve of theobromine o-acetoxybenzoate shows considerable Merences. It is not unlike that of theobromine itself but narrower and the ultimate effect is comparable with that of salicylic acid and o-acetoxybenzoic acid described above. Solutions of caffeine and caffeine salicylate show similar pheno-mena to theobromine and theobromine salicylate. Cageine benzoate cageirze citrate cageine hydrochE0n'd.e. Soh-Camphor sazicyhte 2774 PURVIS THX ~ I J E X C L OF DIFE"EBIENT NUCLEI tions of these salts give results like those of the base itself except in regard to the positiom of the bands which vary according to the molecular weighta. The author (J. 1915 107 966) showed that benzoic wid has a weak band at lfh3600 (k2770) and also that there was a rapid step-out of the rays from about 72320 into the FIG.2. OscilEdion frequencies. 30 32 32 36 38 40 42 44 U m e r curues. I Phmzone. 1 I .-Lower curves. I (continuous) Quinine. 1 -28mm. M/2000 -Fi ~ 2 8 m r n . E M/20000 .x, 3 2 % - 5 28mm. 2 1M/2000 x - s G --28 rnm. -* 211/20000 I1 PhAazone salicylste. I1 (dash) Quinine saZicylate. I11 (d.aah and dot) Quiaine o-acetoxybeneoate, Schumann region. Hartley and Hedley earlier (J. 1909 91 314) had indicated the presence of the weak band only. It is clear, therefore that the acid nucleus has not affected the general form of the caffeine absorption. Neither citric acid nor hydrochloric acid gives specific absorption in these ultra-violet regions.The curves have not been reproduced. The curve shows (Fig. 2 upper curves) that phenazone has two wide bands at 1/13600 (X2776) Phnazone ; phenazone salicykrte ON THE ABSORPTION SPECTRA OF SWSTBHOE~. 2775 and l/A4150 (~2409). The salt shows a rapid extension of the m p between 1/X3050 (A3270) and 1/X3260 (X3066) and two weak bands a t l/A3400 (BW) and 1/h4100 (l2438). Aa in theobromine and caffeine the rapid extension of the rays may mean the remnant of the less refrangible band of salicylic acid. Hartley (Phil. Tram. 1885 176 471) first described two bands in solutions of quinine at about 1/A3100 (13225) and 1/X3600 (2770). Dobbie, Lauder and Fox (J.? 1911 99 1254; 1912 101 77) described a third weak band at 1/X3740 (h2670).The author has repeated these experiments and fin& only a very weak indication of this third band. The curves (Fig. 2 lower curves) show that the original quinine bands have sdered some changes in strength and position in the salicylate. Both the bands of the salicylate are w d e r than those of the base. In the case of the o-acetoxybenzoate there is a return to phenomena not unlike those of the base itself and there is a shift back nearer to the latter. These changes are comparable (although the differences are not so great) with those of salicylic acid and o-acetoqbemoic acid and of theobromine and its salts described above. The rapid extension of the rays from l/A4100 is noticeable in all three substances. ResuZts.-The chief results of these observations are (1) the bands of phenyl benzyl thymol and camphor salicylates are com-parable with those of salicylic acid the differences from the latter, and from one another being chiefly in position and strength; (2) the basic nucleus is the chief agent in the specific absorption of the benzoate citrate and hydrochloride of caffeine ; (3) in the salicyl-ates of theobromine caffeine phenazone and quinine the acid nucleus modifies that of the basic nucleus to a larger extent but least in the quinine compound (4) in o-acetoxybenzoic acid and in the o-acetoxybenzoates or' theobromine and quinine the replacement of the hydrogen of the hydroql group by the acetyl group exerts a very great influence on the final absorption.It is clear therefore that the specific and the general absorption of these substances depend upon three factors; (a) the nature of the base ( b ) the nature of the acid and ( c ) the presence of hydrogen in the hydroxyl group.Now benzoic acid has a very weak band at 1/A3600 (x2777) and phenol a very strong one at 1p670 (2720). The carboxyl group in the one and the hydroxyl group in the other destroy the well-known bands of benzene and the hydroxyl group replaces these by a much stronger one than is produced by the carboxyl group. It appears from these experiments that the replacement of the hydrogen atom of the hydroxyl group by another radical not itself possessing any specific absorption decreams the Quinine quinine salicylate quinine o-metoxybenzoate 2776 GOSS AND INGOLD THE POSSIBLE ENHANCED absorption capacity of the other parts of the molecule or to put it another way the vibration of this hydrogen atom is a very powerful factor in the absorption. PUBLIC HEKLTH CHEMICAL LABORATORY, CAMBRIDGE. [Received September 14th 1925.