Tetra hydro cymene

CH / H3C CH3 Tetra-hydro cymene 1 CH / H3C CHa Heza-hydro cymene ... 

The tetra-hydro cymene containing one double bond or ethylene group is known as menthene or a terpene, while the di-hydro cymene containing two double bonds is named mentha-di-ene, a terpa-di-ene. The terminology and its significance will be recognized as exactly the same as used in the naming of the unsaturated aliphatic hydrocarbons... 

Isomerism.—From an examination of the above formulas it will be seen that the positions occupied by the added hydrogen atoms in the original cymene molecule or, what is the same thing, the positions occupied by the double bonds, makes isomerism possible both in the tetra-hydro cymenes or menthenes with one double bond and the dihydro cymenes or mentha-di-enes with two double bonds. In the former case six isomers are possible while in the latter there are fourteen. This will be clear if we give the skeleton formulas for the six possible menthenes. 

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