Chemistry Reference
In-Depth Information
(
Mentha piperita
, Labiatae) oil], (
+
)-neomenthol (
E8
) [a constituent of Japanese
peppermint (
Mentha arvensis
) oil], and (
−
)-neoisomenthol (
E9
) in geranium
(
Pelargonium roseum
, Geraniaceae) oil. The unsaturated versions of
p-
menthol,
namely
p
-menthenol, exhibit extensive regioisomerism and are represented
by (
−
)-pulegol (
E10
) (a constituent of several peppermint (
Mentha gentilis
and
M. spirata
(Labiatae) oils), (
−
)-isopulegol (
E11
)(in
Mentha rotundifolia
(Labiatae)), (
−
)-piperitol (
E12
) (in several
Mentha
and
Eucalyptus
species),
(
−
)-
α
-terpineol
(
E13
) in
Artemesia
,
Eucalyptus
,
Juniperus
,and
Mentha
species), and (
)-carveol (
E14
). Oxidation products of both saturated and
unsaturated cyclohexane monoterpene alcohols also occur in nature. Of these,
the most abundant in the plant kingdom are (
−
)-menthone (
E15
) (in peppermint
(
Mentha
x
piperita
) oil), (-)-isopulegone (
E16
)(inoilof
Mentha pulegium
),
(
−
)-piperitone (
E17
)(in
Eucalyptus
oil), and (
+
)-carvone (
E18
)(inripe
fruits of dill (
Anethum graveolens
, Umbelliferae) and caraway (
Carum carvi
,
Umbelliferae)).
Aromatic versions of cyclohexane monoterpenes (benzenoid menthanes or
cymenes) are also found in nature and are constituents of some plants fre-
quently used as spices. The hydrocarbon
p
-cymene (
E19
) has been found to
occur in the oils of cinnamon (
Cinnamonum zeylanicum)
, cypress, eucalyptus,
thyme, and turpentine, whereas
m
-cymene (
E20
) is a constituent of the oil of
blackcurrant (
Ribes nigrum
, Saxifragaceae). The corresponding phenols, thymol
(
p
-cymen-3-ol) (
E21
) and carvacrol (
p
-cymen-2-ol) (
E22
), have been found to
occur in many plants. Thymol (
E21
) is a constituent of thyme (
Thymus vul-
garis
, Labiatae) and
Orthodon angustifolium
(Labiatae). Carvacrol (
E22
)has
been found to occur in oils of thyme, marjoram, origanum, and summer savoy.
Additional chemical diversity of monoterpenes is apparent from the natural
occurrence of their bicyclic analogs that bear cyclopropane (carane and thu-
jane types), cyclobutane (pinane type), and cyclopentane (camphene/bornane,
isocamphane and fenchone types) rings (Figs. 1.6 and 1.7). The carane type of
bicyclic monoterpenoids in plants is represented by (
−
)-3-carene (
F1
) that occurs
in
Pinus longifolia
(Pinaceae) and the related carboxylic acid, (
+
)-chaminic acid
(
F2
), in
Chamaecyparis nootkatensis
(Cupressaceae). Compared with caranes,
the thujane type of monoterpenoids is more abundant in plants. The hydrocar-
bon analog (
+
)-3-thujene (
F3
) has been found to occur in the oils of coriander
(
Coriandrum sativum)
,
Eucalyptus
,and
Thuja occidentalis
(Cupressaceae). Its
regioisomer, (
+
)-sabinene (
F4
), occurs in
Juniperus sabina
(Cupressaceae). The
hydration product of (
−
)-3-thujene, namely (
−
)-thujol (
F5
), occurs in plants
belonging to the genera
Thuja
,
Artemesia
,and
Juniperus
, whereas the corre-
sponding ketone (
+
)-3-thujanone (
F6
) is found in the oils of several plants of
the families Asteraceae, Labiatae, and Pinaceae.
Pinane-type bicyclic monoterpenoids (Fig. 1.6) occur in the wood of several
species of
Pinus
. The most abundant are
α
-and
β
-pinenes (
F7
and
F8
,
respectively). Allylic hydroxylation products of pinenes, (
+
)-verbenol (
F9
),
(
+
)-myrtenol (
F10
), and (
−
)-pinocarveol (
F11
) also occur in nature together
with their products of oxidation: (
+
)-verbenone (
F12
), (
+
)-myrtenal (
F13
), and
−
