INVESTIGATION WITH A ROCK-SALT PRISM. 8l 



Safrol. CioHioO.. (Fig. 87.) 



In safrol quite a number of points are to be 



^C^H2-CH = CH2 noticed. It is far more opaque than benzene out 



]| I to 12 IX, where it becomes more transparent. As 



H*^\ -i^'^^CH? in several other benzene derivatives, the absence 

 C — O "^ , ..... 



of common transmission minima is conspicuous, 



except the one at 12.9 yu.. The 9.1 /x band is also to be found in other 

 compounds not related to benzene, e. g., piperidine, which has a ring of 

 CHa-groups. The curve, b, of safrol, at 3.42 ^ was obtained by using 

 the large spectrometer. It shows the absence of the 3.25 /a band of ben- 

 zene, while the 2.9 /a band of eugenol, to which it is related, is very small. 

 In safrol the bands are sharp and deep, and are of importance in con- 

 nection with the idea propounded by Abney and Festing^ that the O atom 

 sharpens the absorption bands. The large spectrometer failed to detect 

 new bands at 3 11, but several were found at 6 /x. This is an example 

 where the benzene ring vibration is almost entirely overshadowed by 

 that due to the preponderance of CHg-groups. 



CUMENE (ISOPROPYL BEN^ZNE). CeHr— CH=(CH3)2. (Fig. 84.) 



In this compound we have the original benzene ring complete, except 

 for one H atom, which has been replaced by a CH-group, to which is 

 attached two CHg-groups. The result is a struggle between the benzene 

 ion and the CHg-groups, and there is a compromise for different parts 

 of the spectrum. Thus the maximum at 3.43 ix is a little greater than 

 that for mesitylene, in which three CHg-groups are joined directly to 

 the benzene ring. At 6.2 /a we have the band common to the xylenes. 

 At 6.65 /A there is a new band. At 6.86 /a we find the mesitylene band, 

 while at 9.75 fx we have the band found in benzene, in orthoxylene, and 

 in numerous other compounds not related to the benzenes. At 13.4 /* 

 we have a deep maximum like the one in orthoxylene at 13.6/*. As a 

 whole this compound behaves like the xylenes, anisol, and mesitylene, 

 which strengthens the argument for CHg-groups, especially for their 

 bonding with the benzene nucleus. 



iCymene. C10H14. 



H Cymene is obtained from caraway, and can also 



^-./'^^^ _ be prepared from turpentine oil and thymol. On 



II 1 (^jj comparing cymene with the terpene group of 



^^\.^<;#=^~^^"^CH3 curves, we see that the general transmission is in 

 H two steps remarkably like the terpenes, while 



there are quite a number of transmission minima in common. Cymene 

 is the more transparent of the two, but, like pinene, has three CH3- 

 groups. 



^Abney & Festing, loc. cit. 



