64 INFRA-RED ABSORPTION SPECTRA. 



The 343 /i, 6.86 /i, 9.3 /a, and 13.6)11 bands are found in the petroleum 

 distillates. The great difference between this curve and that of the 

 iodides is significant of the effect produced by introducing such ele- 

 ments as I, S, and N into the methyl and ethyl compounds. 



Allyl Sulphide. (C3Hs)2S. (Fig. 42.) 



H H2 The structural formula of this compound shows that 



H2C=C— C\^ ^hg CHg-groups of atoms predominate. There are also 

 UiC=C—c/ two CH-groups. But when we compare the absorp- 



^ ^2 tion curve with that of piperidine, which compound has 



a ring of CHg-groups, we find so similarity between them. The same 

 is true when compared with benzene (CeHg), which has a ring of CH- 

 groups, so that the compound seems to have a spectrum peculiar to itself, 

 and the question of groups of atoms is of less significance than the 

 manner of bonding of the groups with others in the molecule. In gen- 

 eral, the sulphides have been found quite transparent. Allyl sulphide 

 is an exception, which, according to Friedel,^ is to be accounted for by 

 the preponderance of H atoms. 



Ethyi, Sulphate. (C2H6)2S04. (Fig. 43.) 



This compound decomposes when exposed to light. The sample 

 used was distilled just before using. The distilling had to be done 

 fractionally under reduced pressure. Since the best sample obtained 

 had a slight odor of SO2, the exploration of its absorption spectrum was 

 not continued beyond 7 ix, where there was complete opacity for the 

 cell used. The 3.45 ix and 5.95 fi transmission minima are of interest 

 in considering the action of the ethyl radical. 



Methyl Acetate. CH3OOCH3. (Fig. 45.) 

 Methyl acetate belongs to the fatty acids and shows some similarity 

 to that group. The region at 3.3 /x reminds one of phenyl acetate, 

 while at 1 1 ju, the transparent region is similar to that of alcohol. 



This compound is very opaque, and its study has not aided materially 

 in determining the effect of CHg-groups. The region of great opacity, 

 from 6 to 9 yu,, is to be found in methyl carbonate, ethyl succinate, and 

 several other compounds containing oxygen. 



Acetone. CHsCOCHs. (Fig. 46.) 



Acetone differs from methyl acetate in having a C atom substituted 

 for an O atom in the latter. 



^Friedel, loc. cit. 



