1. STEREOCHEMICAL THEORY OF
OLFACTION
The Stereochemical theory of olfaction states
that a molecule's particular smell is due to a 'lock
and key' mechanism by which a scent molecule
fits into olfactory receptors in the nasal epithelium.
Stereochemistry, a subdiscipline of chemistry, involves the study
of the relative spatial arrangement of atoms that form the structure
of molecules and their manipulation. An important branch of
stereochemistry is the study of chiral molecules.
Stereochemistry is also known as 3D chemistry because the prefix
"stereo-" means "three-dimensionality".
The study of Stereochemistry focuses on stereoisomers.
stereoisomers.are isomeric molecules that have the same
molecular formula and sequence of bonded atoms (constitution),
but that differ only in the three-dimensional orientations of their
atoms in space. This contrasts with structural isomers, which share
the same molecular formula, but the bond connections and/or their
order differ(s) between different atoms/groups. In stereoisomers,
the order and bond connections of theconstituent atoms remain the
same, but their orientation in space differs
There are 2 types of stereoisomers:

2. ENANTIOMERS
In chemistry, an enantiomer is one of two stereoisomers that are
mirror images of each other that are non-superposable (not
identical), much as one's left and right hands are the same except
for opposite orientation.

3. S-lactic acid and L-lactic acid
Chirality
A chiral molecule is a type of molecule that has a non-
superposable mirror image. The feature that is most often the cause
of chirality in molecules is the presence of an asymmetric carbon
atom.
In chemistry, chirality usually refers to molecules. Two mirror
images of a chiral molecule are called enantiomers or optical
isomers.
Diastereomer:
Diastereomers (sometimes called diastereoisomers) are
stereoisomers that are not enantiomers. Diastereomerism occurs
when two or more stereoisomers of a compound have different
configurations at one or more (but not all) of the equivalent
(related) stereocenters and are not mirror images of each other
. L-tartaric acid

4. D-tartaric acid
DIASTEREOMERS
Olfaction is the sense of smell. This sense is mediated by
specialized sensory cells of the nasal cavity of vertebrates, and, by
sensory cells of the antennae of invertebrates.
OLFACTION depends on the structure of particular molecule.

5. Human olfactory system. 1: Olfactory bulb 2: Mitral cells 3:
Bone 4: Nasal epithelium 5: Glomerulus (olfaction) 6:
Olfactory receptor cells
Detection of odors
1.The initial detection of odors takes place at the back of the
nose in a small region known as the olfactory epithelium.
2.Dissolved molecules interact with specialized receptors called
odorant-binding proteins. (Odorants are molecules that
stimulate the olfactory receptors.)

6. 3.The binding of the molecules to these receptors initiate an
electrical signal that transmits to the olfactory bulbs and
higher brain centers for processing of the olfactory
information.
4.To distinguish the smell, the brain must then determine
the precise combination of receptors that are activated
by a particular odor.
SO, olfactiondepends on the structure of particular molecule.
Odorants must be volatile
Odorants are nonionic compounds,It must be volatile at
ambient temperature, so that the molecule can reach the
nose. It must interact with the protein odorant receptor
sites in the nose.

7. VOLATILE OILS
Volatile oils are the odorous principles found in
various plant parts.
STEREOISOMERS, VOLATILE OILS AND
OLFACTION:
1.
(VOLATILE OIL)
STEREOISOMER(CONSTITUENT OF Orange
and Lemon)
Smells differently

8. 2.
(VOLATILE OIL)(+ )Carvone smells like Mint and(-
)Carvone smells like Caraway
3.One stereoisomers of PHENANDRENE smells
likeeucalyptus andother smell likefennel.
α-Phellandrene(Smells like Eucalyptus)
β-phellandrene(smells like fennel)
Because molecules of volatile oils bind to specific proteins
in nasal cavity called olfactory receptors .Each olfactory

9. receptor can only bind molecules that have a
complementary shape, just as right hand will only fit into
a right-handed glove, and that's how brain distinguishes
between the scent of the the two stereoisomer molecules
bind to olfactory receptors on different nerve endings in
nose.