8. “the branch of chemistry concerned
with the three-dimensional
arrangement of atoms and
molecules and the effect of this on
chemical reactions”
1. Conformational isomers differ only
by rotation around single bonds.
2. Configurational isomers require
breaking and reforming bonds to
interconvert.
13. • Conversion of cis/trans or trans/cis isomers
• compound heat to high temp. or absorb light.
14. Geometric (cis/trans) isomerism in cyclic compounds
• show no rotation about C-C in cyclic compounds
• atleast two other groups beside hydrogen on the ring
• bulky groups must be on different ring carbon atom
18. Polarized light
“light that has been pass through a polarizing prism
(nicol prism). As a result light vibrates in one plane,
19. Polarized light
• The polarimeter measures the rotation of plane
polarized-light, that has passed through a solution.
• Rotation, in degree is, [α]
• Right rotation = Clockwise [+] = dextrorotatory (d)
• Left rotation = Anticlockwise [-] = levorotatory (l)
20. Optical isomerism
“A plane which divides an object into two symmetrical
halves is called plane of symmetry; that object is said be
Achiral (symmetric)”
An object lacking plae of symmettry is called Chiral
(dissymmetric) or asymmetric.
21. Optical isomerism
• non-superimposible mirror images are called
enantiomers.
• isomers that are not mirror images are called
diastereomers.
• the bonded to
is called asymmetric carbon atom.
24. Optical isomerism
• Optically active molecule cannot be superimposed
on its mirror image, also called Chiral molecule.
• Recemisation is the conversion of optically acttive
compound into a recemic mixture.
25. Optical isomerism
• Recemic mixture is mixture of equal parts of
enantiomers (50d:50l). This type of mixture is
optically inactive.
26. Optical isomerism
• Meso compounds has
, and superimposible on its mirror image.
Optically inactive
27. Optical isomerism
• Resolution of recemic mixture is the saperation of
enantiomers ( d and l isomers) into an optically active
components (+ and -).
• Recemic mixture can be resolved by two methods:
1. Chemical
2. Bio-chemical
28. Optical isomerism
• Resolution of recemic mixture
1. Chemical resolution
Recemic mixture is made to combine with another
optically active compound, differences are setup,
which exploit saperation.
A recemic mixture of optically active base can be
saperated by the use of an optically active acid.
30. Optical isomerism
• Resolution of recemic mixture
2. Biochemical resolution
When certain bacteria or moulds are added to a
solution of a recemic mixture they bring about
decomposition of optically active form more rapidly
than others.
31. Optical isomerism
• Resolution of recemic mixture
2. Biochemical resolution example: racemic tartaric
acid can be resolved with the aid of certain penicillin
molds that consume the dextrorotatory enantiomer
faster than the levorotatory enantiomer; pure (-)-
tartaric acid can be recovered from the mixture:
32. • Text book of Organic Chemistry by BS Bhal
and Arun Bhal
