594 REPORT— 1903. 



I would suggest that for the future evidence from their spectra be taken into 

 account in studying their constitution. 



Stereo-i$07nerism in the Alkaloids. 



Many alkaloids having the same formula are stereo-isomerides, and those related 

 in this manner exhibit molecular absorption curves which are identical. The 

 following examples are quoted by Dobbie and Lauder (1903) as the result of their 

 investigations : dextro-corydaline and inactive corydaline ; narcotine and gnosco- 



Eine ; tetrahydroberberine and canadine. Where two compounds are known to 

 ave the same formula, and one of these is optically active, the other inactive, it 

 may be inferred, as Dobbie and Lauder have pointed out, that they are not 

 optical isomerides if their absorption curves are different ; thus canadine and 

 papaverine have the same formula, but their absorption curves show that they are 

 structurally different. 



It is a general rule that substances which agree closely in structure exhibit 

 similar series of absorption spectra, while those which differ essentially in structure 

 show absorption curves which are diti'erent ; and to this rule neither aromatic 

 compounds, alkaloids, nor dyes and coloured substances form any exceptions. 

 That this is so is easily understood from the theory of absorption spectra. It 

 must, however, be distinctly understood that the essential feature of importance in 

 all such investigations is the quantitative relation of the substance to its spectra, 

 whether these relations are based upon equal weights of material or equimolecular 

 proportions in solutions of given volume and thickness. 



The relationship of morphine, C],H,,NO(OH),j, and codeine, or methylmor- 

 phine, Cj,H,-N0.(0n)(0CH3), was shown by their spectra, the latter being a 

 homologue of the former. A similar instance has been investigated recently 

 by Dobbie and Lauder. The resemblance between the spectra of laudanine, 

 C20H05O4N, and laudanosine, O.jiHj^O^N, confirms the view that they are homo- 

 logous bases. The close agreement of their absorption curves with those of 

 corydaline and tetrahydropapaverine clearly indicates a similarity in structure 

 to that of these alkaloids, but the relationship of laudanosine to corydaline is 

 probably closer than to tetrahydropapaverine, and may be best explained by the 

 formulae 



C„,H,,0,N-CH., + IL = C,,H„-0,N 



Corydaline. Laudanosine. 



The removal of a methyl group from such a compound would scarcely cause 

 any appreciable change in the curve of molecular vibrations, and very many cases 

 are known where, when two atoms of hydrogen are introduced into a compound 

 without altering the close linking of the carbon atoms of the ring formation in the 

 compound, the alteration in the spectrum is insignificant. 



A particularly interesting example of tautomerism already mentioned has been 

 observed by Dobbie and Lauder in studying the constitution of cotarnine, a sub- 

 stance prepared from narcotine. Three formulte have been proposed for it : one 

 represents it as an aromatic aldehyde in which one hydrogen is replaced by an 

 open change containing nitrogen ; a second gives it the character of a carbinol 

 base ; while a third that of an ammonium base. It has been supposed that in 

 solution it is a mixture of two or all three such substances in a state of 

 equilibrium, but as to what is the formula to be assigned to solid cotarnine the 

 data are insufficient to determine. There are, however, two different solutions of 

 the substance obtainable : that in ether or chloroform is quite colourless, like 

 the solid ; but a solution in water or alcohol is yellow. From the molecular 

 absorption spectra of these solutions and of certain derivatives with which they 

 are compared there is very distinct evidence that a solution in alcohol or water 

 contains the ammonium base, while under the influence of sodium hydroxide 

 it assumes the condition of the carbinol form. Moreover, the rate of transforma- 

 tion and the conditions which influence this isomeric change have been studied. 



