148 CHEMISTRY OF PLANT LIFE 



or medicinal properties, their structure has been well worked out, in 

 most cases; but it seems to be hardly worth while to present these 

 matters in detail here, as they are of interest chiefly on account of 

 their medicinal properties rather than their botanical functions. 



Borneol, CioHiTOH, and menthol, CioHigOH, are typical 

 alcohols. The latter is a crystalline substance, which melts at 

 42, which is present in peppermint oil, both as the free alcohol 

 and as an ester of acetic acid. 



Amyl acetate, CHs-COOCsHn, and linalyl acetate, 

 CHs-COOCioHiT, the latter occurring in the oils of lavender and 

 bergamot, are typical esters classed as essential oils. 



As examples of the aldehyde oils, benzoic aldehyde, 

 "oil of bitter almonds," and cinnamic aldehyde, 

 CHCHO, found in the oils of cinnamon and cassia, may be cited. 



Camphor, CioHieO, is a ketone, having the following structural 

 formula: 



There are a considerable number of essential oils which are 

 phenols. Thymol, C 6 H 3 (CH 3 ) (C 3 H 7 ) OH, in oil of thyme, and 

 carvacrol, its isomer, in oil of hops, are familiar examples. 



/O C=0 



Coumarin, the anhydride of cinnamic acid, CeH4\ , 



HC=CH 



is an example of an acid substance which is classed as an essential 

 oil, even though it is a solid at ordinary temperatures. It has an 

 odor and flavor similar to that of vanillin, the essential flavoring 

 material of the vanilla bean, and is often used as a substitute for 

 .the latter in the preparation of artificial flavoring extracts. 



Of the essential oils containing sulfur, there are two common 

 examples; oil of mustard, allyl isosulfocyanide, CsHsNCS, and 

 oil of garlic, allyl sulfide (CsHs^S. The latter is present in 

 onions, garlic, water cress, radishes, etc., the difference in flavor of 

 these vegetables being due to the fact that the allyl sulfide is 

 united with other different groups in the glucoside arrangement, 



