With any new discipline comes corresponding language foreign to what we’re used to. Within that discipline are sects with their own dialects, such as the analytical cannabis lab, extraction facility, or grow. Like mastering Spanish or American or Sumerian, to extract knowledge requires understanding of what the words mean.
Terpene v. Terpenoid
Often, the word terpene relates many different molecules like limonene or pinene or caryophyllene. Sometimes for simplicity, this term is used even when the molecules aren’t technically terpenes, but rather terpenoids like linalool or geraniol or fenchol. The difference lay in what elements comprise the molecule. If carbon (C) and hydrogen (H) are the only two elements present, it’s a terpene. If another element like oxygen (O) is present, it’s a terpenoid. Alcohols have -OH groups in their molecular structure and their names end in -ol, so geraniol, linalool, bisabolol, etc. are indeed terpene alcohols. These substances may also be dissected into their individual terms like fenchyl alcohol or linalyl alcohol, but they mean the same thing (like isopropanol and isopropyl alcohol).
Terpenes have vapor pressures between 100-550 Pa at 25°C (77°F).  Terpenoids have vapor pressures between 1-130 Pa [at 25°C (77°F)]. When a substance has a high vapor pressure, it more readily vaporizes into a gas (has higher volatility).
Monoterpene v. Sesquiterpene
There are other names used to describe terpenes, such as monoterpenes and sesquiterpenes. Their difference also revolves around their chemical structure. A monoterpene has 10 carbon and 16 hydrogen atoms. Monoterpenes include myrcene, terpinene, and sabinene. A molecule may also be listed as a monoterpenoid, examples of which include monoterpenoid alcohols like terpineol or borneol, as well as monoterpenoid ketones like camphor.
The sesquiterpene is bulkier, having 15 carbon and 24 hydrogen atoms. The most common sesquiterpene is beta-caryophyllene; however, others include cedrene, farnesene, and humulene. And there are also sesquiterpenoids like bisabolol, guaiol, and nerolidol (alcohols), or germacrone (ketones).
Monoterpenes are often more volatile than sesquiterpenes. Because they are more readily promoted into vapor, monoterpenes strongly contribute to the characteristic scents of a plant, releasing olfactory molecules into the air to waft into our noses. Sesquiterpenes definitely contribute to a plant’s aroma as well, but their organic chemistry enables a greater resilience to hang back in the plant.
The need to save the terpenes is increasingly important. This can be exemplified in cannabis cultivation and extraction. Concentrations of monoterpenes may be diminished when curing biomass which is why some growers/processors flash-freeze flowers, creating “live” products. Cured flower products continue to lose terpenes when ground. In an interview with Terpenes & Testing, Michael Backes reported that he “started testing commercial prerolls and found that their monoterpene content was nearly nonexistent.”
Monoterpenes may also be reduced during product refinement stages that involve heat. That’s why options like subcritical carbon dioxide are utilized – to save fragile terpenes. If no efforts are taken to preserve the chemovar, you may be left with plentiful sesquiterpenes like caryophyllene. Organoleptically, the scent and taste of a product with dominant levels of caryophyllene would be expected to contain strong notes of black pepper or clove, which might represent many of the vape cartridges you’ve experienced.
- Fichan I, et al. Water solubility, vapor pressure, and activity coefficients of terpenes and terpenoids. J. Chem. Eng. Data. 1999;44(1):56-62. [journal impact factor = 2.369; times cited = 77 (SemanticScholar)]