INVESTIGATION WITH A ROCK-SALT PRISM. 9I 



shozving that the original benzene vibration has not been seriously dis- 

 turbed. A new band occurs at 3.55 fi. 



/O— CH\CH3. 

 Paraldehyde. C6H12O3. CHsCH^ ,0 (Fig. 107.) 



^O— CH / CH3. 



This is an interesting compound, being a polymer of CH3 groups. 



The conspicuous 5.83 fi band of numerous other CH3 compounds is 

 scarcely noticeable. The first large maximum occurs in the usual place 

 at 3.46 /i., while the 6.86 /x and 7.32 fi bands of many compounds occur at 

 6.9 fi and 7.2 fi. The complex band at 7 /x, is also found in benzalde- 

 hyde and cuminol, and as a whole this band at 7.2 ju, seems characteristic 

 of the aldehydes. It will be noticed that the 1 1.7 /i band of paraldehyde 

 is found shifted to 12. i fi in benzaldehyde and in cuminol, while the 

 13.4 fi band is in common with that of benzaldehyde, which is much 

 broader. The bands are even more marked than in benzaldehyde. 



Cuminol (Cuminic Aldehyde). CgHuCHO. (Figs. 109 and no.) 



This benzene derivative is interesting because 



C~CHO 



Ho^ **^CH of its combination of the benzene ring, of the CH3- 



II L groups and of the aldehyde radical, CHO. As a 



^C^H=(CH3) result the benzene band at 3.25 fi is obliterated, and 

 a complex band occurs at 3.4 /x, the weaker compo- 

 nent lying at about 3.7 /x. The 5.9 /a band is strong, as in benzaldehyde. 

 A complex band occurs at 6.25 fx (benzene?) and at 6.35 fx. The 6.86 fx 

 of the petroleum oils is also present. As a whole, the vibration of 

 the benzene nucleus has disappeared. In comparison with cumene, 

 C6H5CH(CH)3, a marked change has been brought about in the absorp- 

 tion spectrum by the addition of the CHO-group. 



The 12 IX band is to be noticed, since it occurs equally strong in mesi- 

 tylene, where the three CH3-groups are joined directly to the benzene 

 nucleus. The 13 /* band is also found in benzene. 



TEJRPJSNES. 

 This distinctive group of compounds is interesting on account of its 

 manner of occurrence and its unusual characteristics. All compounds 

 have a pleasant odor. Many are optically active, and as a whole this 

 group is an interesting one for study. Considered chemically,^ the 

 constitution of only a few of the terpenes and camphenes has been 

 thoroughly established. They have a closed ring of six members in the 

 simpler "monocyclic terpenes" {e. g., limonene), while in the "complex 

 terpenes" (pinene) the structure is a combination of two rings. 



^Bernthsen : Org. Chem., p. 542. 



