Part 1: The Basics of Essential Oil Chemistry
building blocks called isoprene units, which have five carbons. There
are three main kinds of terpenes: monoterpenes, sesquiterpenes,
and diterpenes. Diterpenes are sometimes present in essential oils,
but only in very small amounts. Their large molecular weight keeps
them from evaporating during steam distillation. Monoterpenes and
sesquiterpenes are the main compounds found in essential oils.
Due to their differences in size and structure, monoterpenes and
sesquiterpenes have different effects on the body.
Monoterpenes are found in
some amount in almost all
essential oils. They have a
structure of 10 carbon atoms
derived from two isoprene
units. Monoterpenes can have
a straight-chain backbone or
a single ring (see figure 2.3).
Due to their smaller size,
they tend to react quickly
to air and heat, and they
Figure 2.3: Some common mono-
terpenes include limonene (top left),
tend to be broken down more
gamma-terpinene (top middle), myrcene
quickly than their more complex
(right), and para-cymene (bottom).
sesquiterpene counterparts.
Monoterpenes have strong effects on cell membranes because they
are small enough to fit between the fatty molecules that make up the
cell membrane. They are also small enough to completely pass through
it and affect targets inside the cell. There are believed to be well over
2,000 varieties of monoterpenes, each with its own unique biological
activity.
Sesquiterpenes have a structure of 15 carbon atoms derived from
three isoprene units. Because of their higher molecular weights,
sesquiterpenes are less volatile than monoterpenes and are
therefore less prevalent in essential oils overall. It is believed that
there are over 10,000 different varieties of sesquiterpenes.
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Part 1: The Basics of Essential Oil Chemistry