98 INFRA-RED ABSORPTION SPECTRA. 



characteristic bands, e. g., the alcohols at 2.95 fi, the mustard oils at 

 4.78 fi, etc., the whole points to a joint effect of bonding and the " nature 

 of the compound," as mentioned by Zsigmondy^ and by Magini.^ This 

 does not elucidate matters very much, for the chemist has already 

 classified the compounds in this manner. 



QuiNOLiNE. C9H7. (Fig. 122.) 

 y H The quinoline group of benzene derivatives have 



^^■\_/^ the same properties as the pyridine group. Quino- 



I II I line is formed by the condensation of a pyridine and 



I^C^ /C\^^" a benzene nucleus. But no close relations are to be 

 H found with them, just as is true of the terpene deriv- 



atives, showing again that the bonding of the groups of atoms in a 

 molecule has great influence on absorption spectra. Quinoline is very 

 opaque, like the pyridines. The only band in common with benzene is 

 at 3.25 IX. 



OTHER CYCLIC COMPOUNDS. 

 ThiophENE. C4H4S. (Fig. 123.) 



In benzene and its extraordinarily large number of 



^^ 9^ derivatives it is quite probable that the six carbon atoms 



HC CH ^^^ joined together in a closed chain or ring. The ques- 



\ / tion as to what sort of chains can exist has been investi- 



gated extensively. It has been found that closed chains of 

 carbon, having three, four, five, or seven carbon atoms, can be formed, 

 those having five or six atoms being especially easy to produce. 



Thiophene^ is one of these rings of five carbon atoms, having one 

 C atom replaced by an S atom. Its derivatives have the same prop- 

 erties as the benzene derivatives. The behavior of thiophene and ben- 

 zene is strikingly different, excepting the 3.22 ^ band, which lies close 

 to that of benzene at 3.2 fx.. Since in each one the ring is of CH- 

 groups, we may assume for the present that the 3.22 fi band is due to 

 this group. Then we look in vain for more bands in common, and. 

 if there are more bands due to CH, they are not to be found by this 

 method of analysis. The thiophene bands at 5.6 /* and 7.3 fi were 

 found in benzene by Julius,* but were not found by the writer, excepting 

 as a slight asymmetry at 7.3 ju,, while the 5.5 fi band was found complex 

 5.4 fi and 5.7 fx.. Since thiophene occurs as an impurity in benzene, it is 

 quite probable that the benzene used by Julius contained a slight trace 

 of it. 



*Zsigmondy, loc. cit. ^See Bernthsen, Organ. Chemie, p. 323. 



^Magini, loc. cit. *Julius, loc. cit. 



