• DEFINITION: Originally, the term “terpene” was employed to describe
a mixture of isomeric hydrocarbons of the molecular formula C10H16
occurring in the terpentine and many essential oils which are
obtained from the sap and tissues of certain plant and trees. The
oxygenated derivatives like alcohols, aldehydes, ketones, etc. at that
time called camphor.
• CLASSIFICATIONS: Class No. of isoprene
1. Isoprene 1 C5H8
2. Monoterpene 2 C10H16
3. Sesquiterpenes 3 C15H24
4. Diterpenes 4 C20H32
5. Triterpenes 6 C30H48
6. Tetraterpenes 8 C40H64
7. Polyterpenes n (C5H8)n
• The monoterpenoids are composed of two isoprene units. These are the simplest natural
occurring terpenoids which are isolated from essential oils obtains from the leaves, roots and
barks of various plant.
• These compounds have pleasant odours and are largely used as perfumery industry.
• Monoterpenoids may be divided into three groups:
1. Acyclic monoterpenes. Example- citral.
2. Monocyclic monoterpenes. Example- menthol
3. Bicyclic monoterpenes. Example- camphor
• It is considered to be the most important member of the acyclic monoterpenes because the
structure of remaining terpenoids in this group are based on the structure of citral.
• It is optically inactive oil with lemon like smell.
• Pale yellow in colour, b.p. 228.C
4. • ISOLATION
lemon grass oil, citral is obtained by its fractional distillation under reduced pressure. This is then
purified by forming the bisulphite compounds the latter compounds further decomposed with sodium
bicarbonate yields, pure citral
• CONSTITUTION OF CITRAL
• Molecular formula- C10H16O.
• Presence of 2 double bond -
As citral adds on two moles of bromine or hydrogen, this shows that it contain 2 double bond
C10H20O C10H16O C10H16OBr4
tertrahydrocitral citral citral tetrabromide
Citral on ozonolysis yields acetone, laevuladehyde and glyoxal. This shows that citral is an acyclic
compounds containing 2 double bond.
5. • PRESENCE OF ALDEHYDE GROUP –
citral forms oximes & reduces Fehling solution therefore O-atom is aldehyde group
Presence of carbonyl group as aldehyde is further confirmed by -
7. B. MENTHOL
• Menthol is an optically active compound.
• Only its (-) form occurs naturally in peppermint oils.
• It’s a saturated compound having melting point 43.C.
• It is used as an antiseptic and an aesthetic.
CONSTITUTION OF MENTHOL -
• Molecular formula- C10H20O
• Presence of alcoholic group - as menthol forms esters readily with acids, this means
that it must posses an alcoholic group.
• Presence of secondary alcohol
The oxidation of menthol yields ketone, indicating that the hydroxyl group in menthol is
secondary in nature.
8. • Presence of p-menthane skeleton-
menthol on dehydration and dehydrohalogention form p-cymene
• Explaining the structure of menthol
9. C. CAMPHOR
• It is the most important constituent of the oil of the camphor.
• Occur in the Cinnamonum camphora.
• It is solid having melting point 180.C and it is optically active
• Uses - as an insect repellent.
- as an mild disinfectant and stimulant for heart muscles.
- for the production of smokeless powders and explosives.
CONSTITUTION OF CAMPHOR-
• Molecular formula - C10H16O.
• Presence of keto group
It form oxime with hydroxylamine
When camphor is distilled with iodine it yields cavacrol.
10. • Presence of –CH2CO group.
When camphor is treated with amyl nitrite and hydrochloric acid, it yields iso nitroso camphor
• Presence of six membered ring
11. • 6. Nature of carbon frame in camphor.
when camphor is oxidized with nitric acid, it yields a crystalline dibasic acid , camphoric acid C10H16O4.
as a camphoric acid possesses the same number of carbon atom as camphor , it means that the keto
group must be present in one of the ring of camphor. Further camphoric acid is dicarboxlic acid and its
molecular refraction reveals that it is also saturated. Thus during the conversion camphor into
camphoric acid , there occur the opening of ring containing the keto group and therefore camphoric
acid must be monocyclic compound.
When camphoric acid is further oxidized with nitric acid , camphoric acid is obtained.
• Diterpenes are a class of chemical compounds composed of two terpene units, often with the
molecular formula C20H32.
• Diterpenes consist of four isoprene subunits.
• They are biosynthesized by plants, animals and fungi via the HMG-CoA reductase pathway,
with geranylgeranyl pyrophosphate being a primary intermediate.
• Diterpenes form the basis for biologically important compounds such as retinol, retinal, phytol and
• Diterpenes can be classified as linear, bicyclic, tricyclic or tetracyclic, pentacyclic, and macrocyclic
diterpenes depending on their skeletal core.
• In nature, they are commonly found in a polyoxygenated form with keto and hydroxyl groups, these
last often esterified by small-sized aliphatic or aromatic acids.
Monocyclic: Vitamin A(retinol)
Tricyclic: Abietic acid, Podocarpic acid
Tetracyclic: Gibberellic acid
• It is a kind of diterpene which comes under the “acyclic diterpene” category.
• Phytol is an acyclic diterpene alcohol and a constituent of chlorophyll.
• It is obtained from alkaline hydrolysis of chlorophyll, which is then converted to phytanic acid and
stored in fats.
• It is commonly used as a precursor for the manufacture of synthetic forms of vitamin E and vitamin K1.
• It is an optically active compound which boils at 145°C at 0.03mm pressure.
• Molecular Formula: C20H40O
• Melting Point: < 25 °C
14. STRUCTURAL ELUCIDATION-
• Molecular formula: C20H40O
• Presence of double bond :
When it is catalytically hydrogenated, it adds on one mole of hydrogen to form dihydrophytol indicating
that phytol contains one double bond.
• Presence of primary alcoholic group :
Phytol on oxidation with chromic acid yields monocarboxylic acid called phytenic acid which has same
no. of C- atom indicating the presence of primary alcoholic group.
• Ozonolysis of phytol :
on ozonolysis it yields glycoaldehyde and a saturated ketone
15. • Structure of saturated ketone may be written as follows :
Structure of saturated ketone is confirmed by its synthesis from ketone(I):
• It is a kind of diterpene which comes under the “Monocyclic diterpene” category.
• It is also called Vitamin A
• Vitamin A is the fat soluble vitamin, is a group of unsaturated nutritional organic compounds that
includes retinol, retinal, retinoic acid, and several provitamin A carotenoids (most notably beta-
• All forms of vitamin A have a beta-ionone ring to which an isoprenoid chain is attached, called a retinyl
• Molecular Formula: C20H30O
18. • Molecular formulae : C20H30O
• Double bond present:
It consumes 5 hydrogen molecules during hydrogenation in presence of Pd catalyst, that means 5 double
bonds are present in the structure.
19. • Isoprene Units Confirmation: The oxidation of Vit.A with Pot. Permagnate gives 2 molecules of Acetic
acid which indicates 2 Isoprene units are present in structure.
• Methyl group: The oxidation of Vit.A in the presen e of CrO3 which gives 3 molecules of Acetic acid. It
means, 3 methyl groups are present.
20. • Hydroxy(–OH) group:
presence of –OH group can be determined by the formation of acetates with acetic anhydride.
Upon Oxidation, Retinol converts to Retinal(aldehyde) and then converts to Retinoic acid. It means, there
is primary alchohol present in structure.
21. • Beta-Ionone Nucleus:
Ozonolysis of retinol gives geronic acid which can directly obtained by ozonolysis of beta-Ionone.It
confirms the basic nucleus of beta-Ionone is present in structure.
• It is a type of Complex diterpene.
• Taxol, a diterpenoid natural product first isolated from Taxus brevifolia, is one of today’s better known
• The paclitaxel molecule consists of a tetracyclic core called baccatin III and an amide tail.
• The core rings are conveniently called (from left to right) ring A (a cyclohexene), ring B (a cyclooctane),
ring C (a cyclohexane) and ring D (an oxetane).
• MOLECULAR FORMULAE – C47H51NO14
• Squalene is a natural 30-carbon organic compound originally obtained for commercial purposes
primarily from shark liver oil (hence its name, as Squalus is a genus of sharks), although plant sources
(primarily vegetable oils) are now used as well, including amaranth seed, rice bran, wheat germ, and
olives. Yeast cells have been genetically engineered to produce commercially useful quantities of
"synthetic" squalane, which is similar to squalene.
28. STRUCTURAL ELUCIDATION
• Molecular formulae: C30H50
• Presence of double bonds :
The molecular formulae of fully saturated squalene was found to be perhydrosqualene with 6H₂
• Absence of conjugated double bonds in squalene:
Squalene fails to undergo reduction whwn treated with Na – metal amd amyl alcohol which indicates
absence of conjugated double bonds
• Oxidation of squalene with chromyl chloride:
On oxidation with CrO₂Cl₂ in CCl₄ gives Formaldehyde , Acetaldehyde ,Succinic acid
• Ozonolysis of squalene :
• Carotenoids are the group of non-nitrogenous , yellow , red or orange pigments that are universally
distributed in living things.
• These are also called tetraterpenoids , that are produced by plants and algae as well as several
bacteria and fungi.
• There are over 600 known carotenoids
• They split into 2 classes xanthophyll and carotenes
• Tetraterpenoids contain 40 C atoms
• General structure of carotenoid is a polyene chain consisting of 9-11 double bonds and possibly
terminating in rings
30. ALPHA & BETA CAROTENOIDS
• About 600- 700 different carotenoids are known of which α & β carotene are the most prominent
• Β carotene is the most known carotenoid and the most often naturally occurring carotene also known
as provitamin A