14 



THE ABSORPTION SPECTRA OF SOLUTIONS. 



In triphenylmethane the limit of the visible portion of the spectrum 

 is reached. It may be stated that anthracene and phenanthrene have 

 entirely different absorption spectra, although the fluorescent spectra are very 

 similar. 1 An auxochrome is a radical that causes the absorption to be more 

 intense. An example is CO C = C CO , which appears in the indigos, 



/CO x /CO 



C,H 4 < 



;C = C 



XH 



XH 



;C 6 H 4 



and also in the deeply colored compounds 



/CO x .CO. CO x XO x 



C 6 H 4 < >C = C< >0 6 H 4 C 6 H 4 /C = C< >C 6 H 4 











s 



s 



The groups CH 3 , OCH 3 , C 2 H 5 , the halogens, etc., are bathochromes, while 

 the groups N0 2 and NH 2 are hypsochromes. 



The infra-red absorption spectra to about 15/* of a large number of organic 

 compounds have been investigated by Julius 2 and by Coblentz. 3 Isomeric 

 compounds are found to possess very different absorption, depending on the 

 combinations of the atoms in the molecule. Stereomeric compounds, on the 

 other hand, were found to possess the same absorption spectra. The replac- 

 ing of hydrogen by an NH 2 or CH 3 group usually results in the appearance 

 of new bands. In the spectrum of certain benzene derivatives, however, the 

 benzene spectrum is usually present. The carbohydrates investigated had 

 characteristic spectra with absorption bands at 0.83 to 0.86/*; 1.67 to 1.72/*; 

 3.25 to 3.43/i ; 6.75 to 6.86/*; and 13.6 to 14/*. The three isomeric xylenes have 

 banded spectra in which the most important line in each group lies farthest 

 toward the long wave-lengths in the order ortho, meta, and para. 



Considerable work has recently been done by Weniger 4 upon the absorp- 

 tion of organic compounds in the infra-red. He finds that the alcohols have 

 bands at 3.0 and 6.9/*; that changes from the primary to the iso-compounds 

 cause small shifts; and that the secondary alcohols have a band at 7.6/* and 

 the tertiary alcohols a corresponding one at 7.9/*. The band 9.6/* in the pri- 

 mary alcohols is shifted to 9.1/* in the secondary alcohols and 8.6/* in the ter- 

 tiary alcohols. There are two minor bands in the primary alcohols which 

 appear as follows: 



1 Elston: Astrophys. Journ., 25, 3 (1907). 



I Verh. Konikl. Akad., Amsterdam, 1, No. 1 (1892). 



3 Invest igal ions of Infra-red Spectra, Carnegie Institution of Washington Publication 



No. 35, by W. W. Coblontz. 



4 Phys. Rev., 31, 408 (1910) 



