THE CHEMICAL HISTORY OF THE TERPENES 57 



far as they have been investigated, range themselves under the 

 following divisions : 



Menthadienes. C 10 H 16 . 



I. Derivatives of cyclohexene : 



i. Para. Limonene and dipentene, terpinene, phellan- 



drene. 

 2. Meta. Sylvestrene. 

 II. Derivatives of cyclohexene with bridged rings : 



i. Para, containing two pentamethylene rings. Fen- 

 chene, camphene ? 



2. Meta, containing one tetramethylene ring. Pinene. 



3. Meta, containing one trimethylene ring. Sabinene, 



thujene. 

 III. Olefinic terpenes with open chains : 

 Myrcene, ocimene. 



A few of the peculiarities of some of the terpenes deserve 

 notice. As already mentioned, pinene is specially remarkable 

 on account of the readiness with which it undergoes isomeric 

 change in contact with almost all agents. This is attributed 

 to the rupture of the tetramethylene ring, whereby cyclohexene 

 derivatives such as terpineol and dipentene are produced. The 

 products of addition present the anomaly that the hydrocarbon 

 cannot be recovered unchanged from any of them with the 

 single exception of the nitrosochloride. That substance, when 

 warmed with an alcoholic solution of aniline, gives the diazo- 

 reaction and behaves as though it contained ready-formed 

 nitrosyl chloride, whilst pinene, identical with the original 

 hydrocarbon in all respects except in being destitute of optical 

 activity, is set free. If methyl- or dimethyl-aniline be used, a 

 nitroso derivative of the base is produced. From these facts it 

 appears that when the nitrosochloride is formed the addition 

 of NO and CI occurs at the double bond in the hydrocarbon 

 molecule which remains otherwise unaltered, thus : 



CH 

 CH 



CH 



I 



NOC1— CMe 



