1«U. KEPOUT — 1900. 



Luxmoore ^ for those pressures. The benzsT/naldoxime was photographed 

 immediately after preparation. It was afterwards recovered from the 

 ethereal solution and the melting point redetermined, when it was found 

 that no decomposition had occurred while the photographs were being taken. 

 These results, which are shown in the above curve, confirm the 

 conclusion previously arrived at, that stereo-isomerides, unlike isomerides 

 which differ in structure, give identical absorption spectra. 



The Ultra-violet Absorption Spectra of some Closed Chain 

 Carbon Compounds.- 



Dlmetliylpyra-inc. 



In a previous report ■^ we gave the results of the examination of the 

 absorption spectra of thiophen, pyrrole, furfuran, and some of the more 

 important furfuran derivatives. Each of these compounds contains 

 two pairs of carbon atoms doubly linked, the chain being closed by a 

 polyvalent element other than carbon. No trace of selective absorption, 

 such as is shown by benzene, pyridine, and many of their derivatives, 

 oould be detected in the spectra of any of these substances. 



We have now extended our investigation to 2 : 5-dimethylpyrazine, 



a substance in which not merely one carbon is replaced by nitrogen in the 

 benzene ring, as in pyridine, but two. It thus belongs to a group not 

 previously examined. 



From the analogy between the constitution of this substance and tliat 

 of pyridine, it was anticipated that it would show a marked selective 

 absorption, and this anticipation proved to be correct. One of the 

 principal reasons for examining a substance of this constitution lay in the 

 fact that whilst pyridine contains the group •C:N- once in the benzene 

 structure, dimethylpyrazine contains it twice, and the orginal formula 

 proposed for cyanuric acid '' contains it three times. Accordingly, if this 

 formula were correct for cyanuric acid and its esters, we should expect 

 that they would exhibit a powerful absorption band, more intense than 

 that of pyrazine, just as that of pyrazine is more intense than tliat of 

 pyridine. But it has been concluded, from a widely extended experience 

 of the behaviour of such substances under the ultra-violet rays, and 

 particularly from the results of a recent examination of the absorption 

 spectra of its derivatives,'' that cyanuric acid does not possess this 

 structure, but one in which the acid is represented by a ring composed of 



•N-C:0 

 three | groups, a mode of single linking resembling that of a hydro- 



H 

 pyridine or of a hydroaromatic group with one carbon replaced by 

 nitrogen ; *• it should not therefore exhibit selective absorption. 



The specimen of dimethylpyrazine used in the experiments was pre- 



' Ttoms. CJiem. Soc, 1896, 69, 177. 



■ Hartley and Dobbie, Trans. Chem. Soc, 1900, 77. 



» Tram. Chem. Soc, 1898, 73, 598. B.A. Report, 1899. 



< Trans. Chem. Soc, 1882, 41, 84. * Hartley, Proc Chem. Soc, 1899, 16, 46. 



« Phil. Trans., Part II., 1885, 519 



