dr. pravin s. jogi
TRANSCRIPT
DR. PRAVIN S. JOGI M.Sc., NET, Ph.D.
HEAD & ASSISTANT PROFESSOR
DEPARTMENT OF CHEMISTRY
JANATA MAHAVIDYALAYA, CHANDRAPUR
ISOMERISM
Same MF with different chemical
structure……
Eg
C2H6O
C
H
H
H
C O
H
H
H
CH
H
H
OC
H
HH
CLASSIFICATION OF ISOMERS
ISOMERS
STRUCTURAL OR
CONSTITUTIONAL ISOMER
• CHAIN
• POSITIONAL
• FUNCTIONAL
• METAMERS
• TAUTOMERS
STEREOISOMERS
• OPTICAL
• GEOMETRICAL
• CONFORMER
WHY NEED TO STUDT STEREOCHEMISTRY ?
The properties of many drugs depends on
their stereochemistry:
Pt
Cl
Cl
NH3
NH3
CIS
Pt
H3N
Cl
Cl
NH3
TRAN
ANTINEOPLASTIC DRUGSNON-ANTINEOPLASTIC DRUGS
Cl
O
NHCH3
R-KETAMINE
Cl
O
NHCH3
R-KETAMINE
ANASTHETICHALLUCINOGEN
The difference in odor between caraway seeds and mint leaves arises
from two stereoisomers of carvone due to different arrangement of
atoms at the carbon (*)
DIFFERENCE BETWEEN STRUCTURAL AND STEREOISOMER
C
H
H
H
C O
H
H
H C
H
H
H
C O
H
H
H STRUCTURAL
STEREOISOMERSC
COOH
CH3
OHHC
COOH
CH3
HHO
• Tetrahedral carbon, Asymmetric carbon
C
H
HH
HBr
Cl
I
F
C
A
B
C
DC DC
A
B
CONVERTION OF TETRAHEDRAL STRUCTURE INTO FISCHER
PROJECTION FORMULA
C
A
B
DC
OBSERVER
A
B
DC
Horizontal-near to observer
Vertical-away from observer
C OHH
CHO
CH2OH
C
CH2OH
CHO
OHH
C
CHO
HOH2C
H
OH
CONVERTION OF 3D INTO PLANER STRU.
CONFIGURATION
•An absolute configuration refers to the spatial arrangement of
atoms of a chiral molecular entity (or groups) and its
stereochemical description. It is determine by X- ray
crystallography.
C
CHO
CH2OHHHO
C
CHO
CH2OHHOH
Methods of determining relative configuration.
Method-1D ,L- configuration: RELATIVE CONFIGURATION
Method-2R ,S- configuration: ABSOLUTE CONFIGURATION
RELATIVE
CONFIGURATION
C
CH2OH
OH
CHO
H C
CH2OH
H
CHO
HO
(+)-GLYCERALDEHYDE (-)-GLYCERALDEHYDE
D and L Assignments
CHO
H OH
CH2OH
D-(+)-glyceraldehyde
Chapter 6 16
COOH
H2N H
CH2CH2COOH
L-(+)-glutamic acid
*
Penultimate carbon is the stereocenter farthest away from the carbonyl group. If the higher priority group is on the left, then (L), if on the right then (D) sugar.
CHO
H OH
HO H
H OH
H OH
CH2OH
D-(+)-glucose
*
*
*
*
*
What is the meaning of……
1.D-(d)-Glucose
2.L-(d)- Glucose
3.D-(l)-Glucose
4.L-(l)-Glucose
CONFIGURATION AND THE R-S
CONVENTION
Rule 1
The atoms directly attached to the stereogenic center are ranked according to atomic
number. The higher the atomic number, the higher the priority
Rule 2
If a decision cannot be reached with rule 1, work outward from the
stereogenic center until a decision is made. Example of ethyl and methyl
below.
Rule 3
Multiple bonds are treated as if they were an equal number of single bonds.
Which group has the higher priority, isopropyl or vinyl?
Assign the configuration (R or S) to the following enantiomer of 3-methyl-hexane
CCH
3
CH2CH
2Br
H
CH(CH3)
2
CH2
O
O
H
H
Example: Name the following compounds.
C
H
Br
CH2CH
3
CH3
CH3Br
CH3H
CH3H3C
ClHH Br
CLASIFICATION OF STEREOISOMERS
1.OPTICAL ISOMERS
2. GEOMETRICAL ISOMERS
3. CONFORMATIONAL
ISOMERS
Optical activity – When a substance rotates
the plane of plane polarized light. (1815 by
Biot)
Plane polarized light – Light that has been
passed through a nicol prism or other
polarizing medium so that all of the vibrations
are in the same plane.
non-polarized polarized
POLARIMETER – An instrument used to measure optical activity.
light source sample tube
polarizer analyzer
DEXTROROTATORY – when the plane of polarized light
is rotated in a clockwise direction when viewed through
a polarimeter.
(+) or (d) do not confuse with D
LEVOROTATORY – when the plane of polarized light is
rotated in a counter-clockwise direction when viewed
through a polarimeter.
(-) or (l) do not confuse with L
The angle of rotation of plane polarized light by an
optically active substance is proportional to the number
of atoms in the path of the light.
Stereoselective and stereospecific
reactions.* *
CH3CH=CHCH3 + Br2 → CH3CHCHCH3
Br Br
2-butene 2,3-dibromobutane
2 geometric isomers 3 stereoisomers
cis- and trans- (S,S)-, (R,R)-, and (R,S)-
meso-
C C
H
CH3
H3C
H
TRAN OR E 2-BUTENE
CH3
BrH
BrH
CH3
MESO-2,3-DIBROMOBUTANE
Bromiation
Br BrCH3
HBr
HBr
CH3
A reaction in which stereochemically different molecules react differently
is called a stereospecific reaction. In this case the cis- and trans-
stereoisomers give different products.
C C
CH3
H
H3C
H
CIS OR Z 2-BUTENE
CH3
BrH
HBr
CH3
CH3
HBr
BrH
CH3
S,S-2,3- DIBROMOBUTANE
R,R-2,3 -DIBROMOBUTANE
Bromiation
Br Br
PRODUCT IS RACEMIC MIXTURE
HOMOTOPIC ATOMS
C C
H
H
H H
HH
C C
H
H
H Cl
HH
C C
H
H
H H
HCl
H By ClH By Cl
ENANTIOTOPIC ATOM
C C
H3C
CH3
H H
HH
C C
H3C
CH3
H Cl
HH
C C
H3C
CH3
H H
HCl
H By ClH By Cl
R-2-CHLOROBUTANES-2-CHLOROBUTANE
n-BUTANE
PRODUCTS ARE ENANTIOMERS OF EACH OTHER
C C
H
HH3C
H
H by ClH by Cl
C C
H
ClH3C
H
C C
Cl
HH3C
H
PRODUCTS ARE DIASTEREOMERS OF EACH OTHER
DIASTEREOTOPIC ATOM
THANK
YOU