Chemical Isomers

1. CHEMICAL ISOMERS

2. What are isomers
Isomers are molecules that
have the same molecular
formula, but have a different
arrangement of the atoms in
space.

3. What are stereoisomers
In stereoisomerism, the atoms
making up the isomers are joined
up in the same order, but still
manage to have a different spatial
arrangement. Optical isomerism is
one form of stereoisomerism.

4. Optical isomers
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. The term chiral in general is
used to describe an object that is not
superposable on its mirror image.

5. A chiral (not chiral) objects are
objects that are identical to their mirror
image. Human hands are perhaps the
most universally recognized example of
chirality: The left hand is a non-
superposable mirror image of the right
hand; no matter how the two hands are
oriented, it is impossible for all the
major features of both hands to
coincide.

6. This difference in symmetry
becomes obvious if someone
attempts to shake the right
hand of a person using his
left hand, or if a left-handed
glove is placed on a right
hand.

7. In medical chemistry, chirality usually
refers to molecules. Two mirror images of a
chiral molecule are called enantiomers or
optical isomers. Pairs of enantiomers are
often designated as "right-" and "left-
handed". Molecular chirality is of interest
because of its application to stereochemistry
in inorganic chemistry, organic chemistry,
physical chemistry, biochemistry, and
supramolecular chemistry.

10. symmetry
The symmetry of a molecule (or any other
object) determines whether it is chiral. A
molecule is achiral (not chiral) when an
improper rotation, that is a combination of a
rotation and a reflection in a plane,
perpendicular to the axis of rotation, results
in the same molecule - see chirality
(mathematics). For tetrahedral molecules,
the molecule is chiral if all four substituents
are different.

11. A chiral molecule is not
necessarily asymmetric
(devoid of any symmetry
element), as it can have, for
example, rotational
symmetry.

12. optical activity: (+)- and (−)- or D and L
An enantiomer can be named by the
direction in which it rotates the plane of
polarized light. If it rotates the light clockwise
(as seen by a viewer towards whom the light
is traveling), that enantiomer is labeled (+).
Its mirror-image is labeled (−). The (+) and
(−) isomers have also been termed d- and l-,
respectively (for dextrorotatory and
levorotatory).

14. Configuration: D- and L-
•An optical isomer can be named by
the spatial configuration of its atoms.
The D/L system, not to be confused
with the d- and l-system, see above,
does this by relating the molecule to
glyceraldehyde. Glyceraldehyde is
chiral itself, and its two isomers are
labeled D and L

15. • The D/L labeling is unrelated to (+)/(−); it
does not indicate which enantiomer is
dextrorotatory and which is levorotatory.
Rather, it says that the compound's
stereochemistry is related to that of the
dextrorotatory or levorotatory enantiomer of
glyceraldehyde—the dextrorotatory isomer
of glyceraldehyde is, in fact, the D- isomer.

16. In biology
• Many biologically active molecules are
chiral, including the naturally occurring
amino acids (the building blocks of
proteins) and sugars. In biological
systems, most of these compounds are of
the same chirality: most amino acids are L
and sugars are D. Typical naturally
occurring proteins, made of L amino
acids, are known as left-handed proteins,
whereas D amino acids produce right-
handed proteins

17. In drugs
• Ethambutol: Whereas one enantiomer is used to treat
tuberculosis, the other causes blindness.
• Naproxen: One enantiomer is used to treat arthritis pain,
but the other causes liver poisoning with no analgesic
effect.
• Steroid receptor sites also show stereoisomer specificity.
• Penicillin's activity is stereoselective. The antibiotic only
works on peptide links of D-alanine which occur in the cell
walls of bacteria - but not in humans. The antibiotic can
kill only the bacteria, and not us, because we don't have
these D-amino acids.
• S(-) isomer of carvedilol, a drug that interacts with
adrenoceptors, is 100 times more potent as beta receptor
blocker than R(+) isomer. However, both the isomers are
approximately equipotent as alpha receptor blockers.

18. •Stereoisomers: isomers that
have same formula and
connectivity but differ in the
position of the atoms in space.
They possess one or more
stereocenters.
•Stereocenter: a carbon atom
bearing 4 different atoms or
group of atoms.

19. • Chiral: any molecule that is
nonsuperposable
• with its mirror image.
• Enantiomers: stereoisomers that are
non superposable mirror images.
• Racemic mixture: a 1:1 (equimolar)
mixture of two enantiomers.
• Optically Active: the ability of some
compounds to rotate plane polarized
light.