Читать книгу Aromatherapy Workbook - Shirley Price - Страница 42

The hydroxyl group (-OH) consists of one hydrogen atom and one oxygen atom; it is not very happy or stable as it has a free arm longing to link with another free arm. When this free hydroxyl group attaches itself to one of the carbons in an aliphatic terpene chain (by displacing one of the hydrogens) it forms an alcohol. Thus a range of alcohols may be formed (none of these is the same as that which occurs in wine and spirits! That is ethyl alcohol, which does not occur in essential oils).

Monoterpenols

When the terpene to which the hydroxyl group attaches itself is a monoterpene, the resulting alcohol is called a monoterpenol and these, like all alcohols, are comparatively easy to recognize as they all end in ‘ol’, for example terpineol, geraniol, linalool (sometimes spelt ‘linalol’) and menthol. They are strong bactericides, anti-infectious, antiviral, stimulating, warming, good general tonics and seen to be free of any hazard, including skin irritation. Because of this, essential oils containing a high percentage of alcohols may generally be regarded as good oils to use on children and the elderly. See Figure 3.11.

FIGURE 3.11: a) Linalool; b) α-geraniol; c) lavandulol, a chain monoterpene; d) α-terpineol, a cyclic monoterpenol

Sesquiterpenols

Should the free –OH group attach itself to a sesquiterpene molecule, it becomes an alcohol called a sesquiterpenol (see Figure 3.12). These are decongestant to the circulatory system, tonic and, like the monoterpenols, also non-irritating. Some have specific actions such as being stimulating to the heart or regenerating to the liver.

FIGURE 3.12: a) farnesol, a chain sesquiterpenol; b) elemol, a monocyclic sesquiterpenol

Diterpenols

These are formed in the same way, by a free –OH group attaching itself to a diterpene molecule. Being heavier, they are not very volatile, so not many of them vaporize and come through the distillation process into the essential oil. However, they are very important, as their structure is somewhat similar to that of human hormones (steroid) and they appear to have a balancing effect on the hormonal system.¹¹ Sclareol (just small enough to vaporize) is a diterpenic alcohol found in clary essential oil and is claimed to be a hormone balancer. See Figure 3.13.

FIGURE 3.13: Sclareol, a diterpenol

So far we have seen the results of attaching the –OH group to molecules made up of hydrocarbon chains of various lengths. Now let us see what happens when this same –OH group joins a hydrocarbon phenyl ring.