86 INFRA-RED ABSORPTION SPECTRA. 



reserved for later discussion, but it is well to keep it in mind in consid- 

 ering the various curves. 



o-ToLUiDiNE. C.H4(CH3)(NH2). (Fig. 96.) 



Considered chemically, this compound is a homologue of the aniline 

 compounds. The absorption curves also show this fact. The substi- 

 tution of the CH3 and the NHo groups has almost obliterated the ben- 

 zene bands, except at 6.75 fi and 1 1 .8 /i. 



The curve of this compound is very similar to that of xylidine, 

 C6H3(CH3)2(NH2), which is to be expected. The large band at 3 ju, 

 is to be noticed, since, like xylidine, it is not resolved. However, the 

 2.96 IX and the 3.43 /j, bands are apparent, as is also the 6.85 ju, band. The 

 6.1 IX band, to be found in compounds having NH2, is shifted to 6.15 /x 

 in this compound. The 8.8 fx band occurs in pyrrol. As a whole, the 

 curve shows bands belonging to CHg, NH2, and CqHq. This sample 

 was distilled just before using. The para modification is solid, and was 

 not examined. 



NITRO DERIVATIVES. 

 Nitrobenzene. CeHsNOa. C6H5N<^q' (Fig. 97.) 



This compound was studied because comparative refractometric 

 investigations by Loevvenherz^ show that the nitro group in nitroethane 

 (C2H5NO2, fig. 33) and in nitrobenzene do not have the same structure. 

 In the latter the N atom is pentavalent, while in the former it is tri- 

 valent. 



The curve shows the benzene bands at 3.25 fx, 6.25 p., 8.62 fx, and 9.8 fx. 

 In the 6.75 fx region the benzene bands are quite obliterated. In this 

 region the CH3NO2 and C2H5NO2 have what appears to be the charac- 

 teristic band of nitrites. The 9.05 fx band is in common with a similar 

 band in these two compounds. As a whole the spectrum is marked for 

 its numerous deep, well-defined absorption bands, especially the one at 

 14.4 fx. The introduction of the NOg-group has not seriously aflfected 

 the benzene spectrum, but, in addition to this, there does not seem to 

 be a characteristic vibration, due to the NOo-group, unless it be the band 

 at 9.05 fi, which band is in common with all the spectra of compounds 

 having N02-groups. 



Ortho and Para Nitrotoluene. CeHiCCHs) (NO2). (Fig. 98.) 



In the xylidines mention was made of the fact that the principal 

 absorption bands shift toward the long wave-lengths, with increase in 

 the nearness of the CHg-groups in the benzene ring. In the present 



^Loewenherz : Zeit. fur Phys. Chera., 6, p. 552, 1890. 



