GENERAL DISCUSSION OF THE SPECTRA. 



117 



that certain bands, e. g., the 3.43 /x band, are due to a definite group of 

 atoms, e. g., the CHj-groups in the chain compounds and terpenes ; in 

 other compounds the evidence is just as strongly in favor of the manner 

 of bonding of the atoms, e. g., the methylene hydrocarbons of the petro- 

 leum distillates ; still other compounds, e. g., benzene and its derivatives, 

 especially phenyl mustard oil, in which we have the characteristic vibra- 

 tion of the mustard oils superposed upon the vibration of the benzene 

 nucleus, show that both the groups of atoms and their manner of bond- 

 ing with other atoms, as well as the kind of atom, have a great influence 

 upon the absorption curve. 



In the present work the spectra have been discussed from the stand- 

 point that since compounds of the same chemical composition (isomers) 

 have different spectra the source of the disturbance is intramolecular. 

 If we had assumed ignorance of the composition of the compounds, we 

 would have expected, from our knowledge of the spectra of the ele- 

 ments, that each compound ought to have a different spectrum. This 

 has been found to hold true, except for certain lines in them, as shown 

 in the following table : 



There would be no reason for deciding whether the cause is inter or 

 intra molecular. The compounds might then be grouped according 

 to the marked absorption bands which they have in common, e. g., 

 those having a band in common at 3.25 ft, at 3.43 fi, or at 4.78 fi. One 

 compound (phenyl mustard oil) would then be placed in the 3.25 fj. and 

 in the 4.78 /u, group. Another (xylidine) would belong to the 2.95^1 

 group and to the 3.43 /a group. This would then suggest a disturbance 

 common to both groups, and we are brought to the point arrived at by 

 the other line of argument, viz, there is a something, call it "particle," 

 "group of atoms," "ion," or "nucleus," in common with many of the 

 compounds studied, which causes absorption bands that are character- 

 istic of the great groups of organic compounds, but we do not know 

 what that " something " is. 



The presence of these groups of ions, each group having its own free 

 period of vibration, is in accord with present conceptions of absorption 



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