This document discusses various methods for determining the structure of terpenoid compounds, including: - Elemental analysis and specific rotation to determine molecular formula. - Esterification rates to determine location of functional groups like hydroxyl and carboxyl. - Reactions like oxidation, ozonolysis, and degradation to break down terpenoids into fragments of known structure. - Physical methods like UV, IR, NMR, and X-ray crystallography provide further structural information. - Considering factors like number of double bonds and rings, along with molecular formula, can reveal the parent hydrocarbon skeleton. Synthetic reactions help confirm or determine unknown structures.

1. Determination of
Structure of
Terpenoid
Prepared by
Dr. N.GOPINATHAN
ASSISTANT PROFESSOR
DEPARTMENT OF PHARMACEUTICAL CHEMISTRY
FACULTY OF PHARMACY
SRI RAMACHANDRA UNIVERSITY
CHENNAI-116
TAMILNADU
INDIA

2. General structural elucidation
• Determination of molecular
formulae of a pure specimen –
elemental analysis.
• If it is optically active, its specific
rotation is measured. It helps to
distinguish the two or more possible
structure as in limonene and
carvone.

3. • Analytical method
• Synthetic
• Physical
• Knowledge of a molecular
rearrangement
• Synthesis

4. Nature of oxygen atom
• Hydroxy group
• Formation of acetates with acetic
anhydride

5. Benzoates with 3,5 dinitro benzoyl chloride

6. Formation of urethane with phenyl iso cyanate
Nature of OH is revealed by esterification rate
primary > secondary > tertiary

7. Carbonyl group

8. Carbonyl group-It can be ascertained by
oxidation to show whether it is a ketone
or aldehyde
Carbon less in number

9. CH2-C=O group

10. CH2-C=O group
in ring on oxidation it yield dicarboxylic acid
without any loss of carbon atom

11. Methyl ketone –COCH3
• Detected by haloform reaction –
oxidation- it yields acetic acid

12. COOH group
• Effervescence with sodiumbicarbonate.
• Number of cooH group is estimated by
titrating with standard alkali
• The point of attachment of COOH to
primary, secondary or tertiary is
determined by rate of esterification.
• primary > secondary > tertiary.
• Tertiary is difficult to esterify.

13. Isopropylidene It is determined by ozonolysis to
acetone. The amount of acetone is estimated
volumetrically and the number of
isopropylidene group is determined
Isopropenyl

14. Presence of unsaturation is ascertained by
addition product.
From number of consumption of H2 molecule the number
of double bond can be estimated
The number of halogen consumed would give the
amount of unsaturation

15. Markovnikoff’s rule

16. Tilden’s reagent
It forms crystalline product having sharp melting
point and be used for identification and
separation of terpenoids.
C=C both are tertiary gives blue colour.
One is tertiary and other is secondary gives
colourless complex

18. Epoxide formation by treated with peracid
Presence of conjugated system can be
determined by the Diel’s alder reaction

19. Number of rings
• From number of olefinic double
bonds, nature of functional
groups and molecular formula of
terpenoid, It is possible to find
out the molecular formula of the
parent saturated hydrocarbon.

20. Example
• Citral C10H16O with two double bond
and one carbonyl group. The molecular
formula of the parent saturated
hydrocarbon.
It is considere with acyclic general formulae
thus citral must be Acyclic

21. From molecular refraction, the nature of carbon
skeleton of sesquiterpenoids can be ascertained

22. Oxidative degradation product
• Degrade the terpenoid to small fragments of known
structure it can be done by oxidation.
• Ozonolysis
• The reagent attack olefinic linkage of molecule to
form ozonide which upon decomposition by
hydrolysis or catalytic reduction yield the
corresponding carbonyl carbon.

23. • Ozonolysis locate position of double bond in
a molecule.
• The formation of acetone and
formaldehyde reveals the presence of
isopropylidene and terminal double bond

24. Oxidation with nitric acid
It is a strong oxidising agent which
drastically degrade the terpenoid
to a mixture of aliphatic and
aromatic acid

25. Haloform reaction

26. Hydroxylating agent – lead tetra acetate in hot
acetic acid, peracid , Osmium tetra oxide,
hydrogenperoxide, potassium per manganate
etc It will form glycols

27. If double bond is in ring on oxidation yield
ketoacid or dicarboxylic acid without loss of
carbon atom.
Alpha pinene on oxidation yield keto acid

28. Dehydration
when terpenoid with alcohol or ketonic group
heated with dehydrating agent, these lose a
molecule of water and converted into simple
aromatic compound

29. When open chain terpenoids are
dehydrated with dehydrating agent they
yield cyclic compound

30. Dehydrogenation
• When terpenoid is heated with Zn, I, Br,S,Se
and palladium they are converted into
aromatic compound of known structure.
• If it is unknown which can be determined
by synthesis.
• By this method the skeleton structure and
position of side chain in original terpenoids
can be determined.

31. Dehydrogenation

32. Synthetic method

33. Grignard reagent
By grignard reaction methyl,
isopropyl can be introduced to
carbonyl alpha terpineol a naturally
occurring terpenoid tertiary alcohol
can be prepared

34. Reformatsky reaction- alpha substituted ester
treated with carbonyl [ aldehyde / ketone /
ester ] in the presence of zinc to form beta
hydroxy ester.later which is treated with dilute
acid to yield beta hydroxy acid which may
further converted to unsaturated acid or
hydrocarbon

35. Physical methods
• UV- detection of conjugation.
• IR
• NMR
• Mass spectroscopy
• Optical rotation
• X ray analysis
• Knowledge about rearrangement
• synthesis

36. THANK YOU