- The document discusses stereoisomerism, which refers to molecules with the same molecular formula but different spatial arrangements of atoms. There are two main types of stereoisomers - optical isomers and geometric isomers. - Optical isomers (enantiomers) are non-superimposable mirror images of each other. They have the same chemical and physical properties except for the rotation of plane-polarized light. Geometric isomers have the same connectivity but different spatial arrangements of functional groups around a carbon-carbon double bond. - The document provides examples of stereoisomers including amino acids, fatty acids, and drugs like ibuprofen and thalidomide. It also discusses how stereoisomers are

1. http://lawrencekok.blogspot.com
Prepared by
Lawrence Kok
Option B Stereoisomers for Protein, Lipids, Carbohydrates,
Vitamin A and iodine number for unsaturated fats.

2. IsomerismMolecules with same molecular formula but diff arrangement of atom
Two types of Isomerism
Positional Chain Isomer Functional Gp Isomer
C – C – C – C – OH
C4H10O1
Structural Isomerism
• Same molecular formula
• Diff structural formula
• Diff arrangement of atom
Diff hydrocarbon chain skeleton
• Same molecular formula
• Same structural formula/ same connectivity
• Diff spatial arrangement of atom
Stereoisomerism
Hydrocarbon Chain Isomer
Diff functional gp position Diff functional gp
C – C – C – OH
‫׀‬
CH3
C – C – C –C
‫׀‬
OH
C – C – C – C
‫׀‬
OH
C – C – C – C
‫׀‬
OH
C – C – C – O – C
Optical IsomerGeometric Isomer
Click here khan organic videos.
Compound Ethane Ethanoic acid
Empirical formula CH3 CH2O
Molecular formula C2H6 C2H4O2
Full SF
Condensed SF CH3CH3 CH3COOH
Stereochemical
formula
(3D)
Isomer Physical
property
Chemical
property
Structural isomer
- Hydrocarbon chain
- Functional gp position
- Functional gp
Different
Different
Different
Similar
Similar
Different
Geometrical isomer Different Similar
Optical isomer Similar Similar
H H
‫׀‬ ‫׀‬
H - C – C – H
‫׀‬ ‫׀‬
H H
H O
‫׀‬ ‖
H - C - C - OH
‫׀‬
H
Structural formula – arrangement atoms in molecule (2/3D)
H H
‫׀‬ ‫׀‬
H - C – C – H
‫׀‬ ‫׀‬
H H
CH3CH3
ethane
Display full SF Condensed SF Ball/stick model Spacefilling
Click here chemical search.
same connectivity but
diff spatial arrangement

3. Geometric Isomers Optical Isomers
Same chemical property– Same functional gp
• Diff physical property – Diff spatial arrangement
(Diff density, solubility, melting pt/boiling pt)
• Same chemical property – Same functional gp
• Same physical property
(Same density, solubility, melting pt/boiling pt)
Vs
Enantiomer
Mirror image of each other
Enantiomer
Mirror image of each other
Stereoisomerism
Molecules with same molecular formula but diff spatial arrangement
• Same molecular formula
• Same structural formula / same connectivity
• Diff spatial arrangement of atom
Cis Isomer
Atom on same side
Trans Isomer
Atom on diff side
click here for optical rotation sugar click here for polarimeter
click here opical rotation corn syrupclick here polarimeter Pasco Demo
Mirror image
Right handed Left handed
Non superimposable
Chiral/asymmetrical/stereocentre carbon
(4 diff groups)
same connectivity but
diff spatial arrangement

4. Isomers with same Molecular Formula and Structural Formula but diff spatial arrangement
• At least 1 asymmetric / chiral carbon / stereocentre , bonded to 4 diff gp
• NH2CH(R)COOH show optical isomerism
• Optical isomers/mirror images call enantiomers (cannot superimpose on each other)
• Similar physical and chemical property except for the effect on rotation of plane of polarised light
• Optically active – enantiomer rotate plane polarised light to one direction (clockwise / anticlockwise)
• Optically inactive – enantiomer present in equal amt (equimolar) – racemic mix and rotation cancel out each other
Optical Isomers
chiral carbon – 4 diff gp
Optically inactive – Rotation cancel out each other
Enantiomer (R) - rotate clockwise Enantiomer (S) – rotate anticlock wise
50% 50% 70% 30%
Optically active – Net Rotation clockwise
Non superimposable
Non superimposable

5. 1. Light pass through 1st polariser – plane polarised light produced
2. Sample introduce to tube. Sample is optically active
Rotate plane of polarised light to one direction
3. Turn analyzer either clockwise/anticlock wise to give light of max intensity again
4. If sample rotate light 120 clockwise – Analyzer need to rotate anticlock wise 120
5. If one enantiomer rotate light 120 clockwise
Another enantiomer rotate light anticlock wise 120
How polarimeter detect optical isomer ?
6. Racemic Mix = enantiomers in equal amt (equimolar) , cancel each other rotation
1st polarizer
1st polarizer
sample optically active
sample optically inactive= Optical activity ability- to rotate plane of polarised light
Optically active isomers
–presence of asymmetrical/chiral centre
- carbon bond to 4 diff gp
Product from natural sources/catalysed by enzyme
• give 1 pure optically active enantiomer
• chiral and found in single enantiomer – optically active
Products synthesised chemically
• give 2 enantiomer in equal amt /racemic mix
• optically inactive rotation cancel out each other
Light source
1st polarizer
Tube containing sample
which able to rotate
polarized light
2nd polarizer
(Analyzer)
Polarizer
tube
Rotated clockwise
How Polarimeter works ?
R – inactive
Racemate mix ibuprofen
S – active
Racemate mix ibuprofenIbuprofen (painkiller)
Click here notes isomers
R limonene S limonene
CH3
CH3
CH3

6. Product from natural source/catalysed by enzyme
• give 1 pure optically active enantiomer
• chiral and found in single enantiomer – optically active
Product synthesised chemically
• give 2 enantiomer in equal amt /racemic mix
• optically inactive rotation cancel out each other
R – inactive
Racemate mix ibuprofen
S – active
Racemate mix ibuprofen
Ibuprofen
(painkiller) R limonene S limonene
CH3
CH3
CH3
Stereoisomerism
Mirror image / enantiomers
Same chemical/physical property
except rotation of polarized light
Source/smell
orange
Source/smell
lemon
Mirror image / enantiomers
Same chemical/physical property
except rotation of polarized light
R carvone S carvone
Mirror image / enantiomers
Same chemical/physical property
except rotation of polarized light
Source/smell
spearmint
Source/smell
caraway seed
R Thalidomide (sedative) S Thalidomide (teratogenic)
• Drug company make drug with R and S (racemic mix)
• Thalidomide exist as optical isomers
• Enantiomers (R) and (S)
• (R) effective against morning sickness
• S teratogenic, birth and limb defect
Our body synthesise enzyme which have active site for only one enantiomer
Mirror image / enantiomers
Thalidomide
(pregnancy)
• (S) cause limb defect / shortening of arm /leg
• (R) is effective drug
• Body convert (R) to (S) by racemisation process, produce racemic mix (R)/(S)
• Most drug in racemic mix equal (R) and (S)
• Cheaper to synthesise racemic mix than pure enantiomer
• Single enantiomer appear to be more effective than racemic mix
• Clinical trial is essential to ensure no harmful side effect
(S), effective as pain relief
(R) has no side effect!

7. Asymmetric/ chiral carbon/ stereocentre , bonded to 4 diff gp
Amino acid Amino acid – pair enantiomers
Stereochemistry in protein
Biologically-active molecule are chiral,
Most are L- amino acid – tasteless
Synthesize D amino acid – sweet
Due to taste receptor in our body
Chiral carbon
D amino acid
Enantiomer(R)
Rotate clockwise
L amino acid
Enantiomer(S)
Rotate anticlock wiseLD
Cis Isomer
Atom on same side
Trans Isomer
Atom on diff side
Stereochemistry in lipids
Geometric Isomers
Long hydrocarbon fatty acid chain
Saturated
(No C = C)
Unsaturated
( C = C)
Fatty acid
Saturated, unsaturated and polyunsaturated
Presence cis /trans isomers
Naturally fatty acids – cis form

8. Cis Isomer
Atom on same side
Trans Isomer
Atom on diff side
Stereochemistry in lipids
Geometric Isomers
Long hydrocarbon fatty acid chain
Saturated
(No C = C)
Unsaturated
( C = C)
Fatty acid
Saturated, unsaturated and polyunsaturated
Presence cis /trans isomers
Naturally fatty acids – cis form
Cis fatty acid
Kink/ bend – unable to pack closely
Weaker intermolecular forces attraction
VDF lower  – m/p lower  - liquid
Trans fatty acid
Straight chain – close packed together
Strong intermolecular forces attraction
VDF higher – m/p high  - Solid
Solidify in arteries – risk heart attack
(artherosclerosis)
Good fatty acid
Mono unsaturated (1 C =C )
Cis transform to trans form
Trans able to pack close together
High m/p – solid form more stable to temp/oxi
High risk – heart attack
Increase level LDL (bad cholesterol)
Polyunsaturated (> 2C = C)
Trans fats (straight)
Convert
H2 Ni catalyst
Cis (bend)
complete
hydrogenation
partial
hydrogenation

9. Lipids chemistry
Rancidity of lipids
Condensation – Form triglyceride
+
Hydrolysis – Glycerol and Fatty acids
Hydrolytic rancidity Oxidative rancidity
Presence H2O/heat
Hydrolysis rxn – (water)- ester link broken
Presence O2/light/enzymes
Oxidative rxn- react with C=C (unsaturation)
Free radical mechanism
LDL vs HDL
LDL
High ratio lipid to protein
More lipid/Less protein
Carry lipid/cholesterol to artery
Bad cholesterol
lipid
protein
HDL
High ratio protein to lipid
More protein/Less lipid
Carry cholesterol from artery to liver
Good cholesterol
VS
lipid
protein

10. Stereochemistry in lipids
Presence cis /trans isomers
Naturally fatty acids – cis form
Cis fatty acid
Kink/ bend – unable to pack closely
Weaker intermolecular forces attraction
VDF lower  – m/p lower  - liquid
Good fatty acid
Mono unsaturated (1 C =C ) Polyunsaturated (> 2C = C)
Omega 3 fatty acid Omega 6 fatty acid
Omega-3 fatty acid reduce blood triglyceride
Increase HDL level - HDL as "good cholesterol" they transport
cholesterol out of blood artery walls, and transport back to liver
Cholesterol carry in HDL away from blood
ALA alpha linolenic acid
(3 cis C=C)
EPA eicosapentaenoic acid
(5 cis C=C)
DHA Docosahexaenoic acid
(6 cis C=C)
3
source omega 3 fatty acid
Linoleic acid
(2 cis C=C)
Arachidonic acid
(4 cis C=C)
Double bond start at C3 Double bond start at C6
Fatty acid Molar
mass
C =C
bond
Melting
point
Linoleic acid 278 3 -11
Linoleic acid 280 2 -5
Oleic acid 282 1 16
Stearic acid 284 0 70
Number C = C increase ↑ (unsaturation ↑)
↓
Lower ability to pack – Due to kink/bend structure
↓
Lower IMF/VDF ↓ between molecule
↓
Melting point decrease ↓ (liquid form)
Iodine number- Measure degree saturation
Iodine number = number gram of I2 react with 100g fat
1 mol Fat – 1 mol I2 (254g I2)
C = C – C = C + 2I2 → C – C – C – C
1 mol Fat – 2 mol I2 (508g I2)
1 C =C in fat
2 C =C in fat

11. Stereochemistry in lipids
Fatty acid Molar
mass
C =C
bond
Melting
point
Linoleic acid 278 3 -11
Linoleic acid 280 2 -5
Oleic acid 282 1 16
Stearic acid 284 0 70
Number C = C increase ↑ (unsaturation ↑)
↓
Lower ability to pack – Due to kink/bend structure
↓
Lower IMF/VDF ↓ between molecule
↓
Melting point decrease ↓ (liquid form)
Iodine number- Measure degree saturation
Iodine number = number gram of I2 react with 100g fat
Linoleic acid C18H32O2.
Determine iodine number of linoleic acid
1 mol Fat – 1 mol I2 (254g I2)
C = C – C = C + 2I2 → C – C – C – C
1 mol Fat – 2 mol I2 (508g I2)
1 C =C in fat
2 C =C in fat
Linoleic acid
(2 cis C=C)
C = C – C = C + 2I2 → C – C – C – C
1 mol linoleic acid – 2 mol I2 (508g I2)
(RMM 280)
280 g linoleic acid – 508 g I2
2 C =C in fat
Iodine number = number gram I2 react with 100g fat
508 g I2 – 280 g linoleic acid
100 g I2 – (280 x 100)/508 g I2
Iodine number = 181
Sample fat contain 0.02 mol fatty acid react with 10.16 g I2
Determine number C =C bonds
0.02 mol acid – 0.04 mol I2
1 mol acid – 2 mol I2 2 C =C in acid
RMM I2 = 253.8
Moles I2 = 10.16/253.8
= 0.04 mol I2
Nutrient Energy/kJg-1
Carbohydrates 17
Protein 17
Lipid 38
Fat - more C- H bond -more reduced
Carbohydrates – more C-O bond–already oxidized
More energy when oxidized/combusted

12. Stereochemistry in lipids
Fatty acid Molar
mass
C =C
bond
Melting
point
Linoleic acid 278 3 -11
Linoleic acid 280 2 -5
Oleic acid 282 1 16
Stearic acid 284 0 70
3 C =C in linolenic
Iodine number = number gram I2 react with 100g fat
Iodine number = 274
274 g I2 – 100 g linoleic acid
761.7 g I2 – 274 g linoleic acid (1 mol)
1 mol linolenic acid – 3 mol I2
2 C =C in acid
RMM I2 = 253.8Moles I2 = 761.7/253.8
= 3 mol I2
Iodine number palmitic acid (Mr = 256) is 0
Iodine number linolenic acid (Mr = 278) is 274.
Determine number double bonds in linolenic acid
Linoleic acid (Mr = 281)
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
Cal vol of 1.00M I2 required to react with 1 g linoleic acid.
Vol 1.0M I2 = 0.00712 dm3 or 71.2 cm3
mol linoleic acid
1/281 = 0.00356 mol
Linoleic acid
(2 cis C=C)
1 mol acid – 2 mol I2 (508g I2)
1 mol acid – 2 mol I2
0.00356 mol acid – 0.00712 mol I2
Find number C = C in linolenic acid, C18H30O2, given
7.7 g I2, react with 2.8 g of linolenic acid.
1–
molg126.902
g7.7
1–
molg278.48
g8.2
:
0.01 mol acid – 0.03 mol I2
1 mol acid – 3 mol I2
mol acid mol I2
3 C =C linolenic
Find iodine number of linoleic acid.
CH3(CH2)4(CH═CHCH2)2(CH2)6COOH Mr (280)
Iodine number = number gram I2 react with 100g fat
C = C – C = C + 2I2 → C – C – C – C
1 mol acid – 2 mol I2 (508g I2)
280 g – 508 g I2
100 g - (508 x 100)/280
= 181 g I2
Iodine number = 181

13. Natural occur sugar –D form
Glucose – 4 stereocenter
C5 – chiral center further from C1
– OH on right
- D form
Enantiomers Diastereomers
Same connectivity
Have chiral carbon
Non superimposable
Mirror image each other
Same connectivity
Have chiral carbon
Non superimposable
No Mirror image
diff chemical/physical property
2 chiral centre 22 = 4 stereoisomer
3 chiral centre 23 = 8 stereoisomer
same chemical/physical property
Mirror image
Not Mirror image
diff configuration at one or more
of equivalent stereocenter
chiral centre
not mirror image
same configuration
mirror image
diff configuration
Enantiomer/mirror image
2n n = chiral centre
D glucose L - glucose
Glucose Isomers
Stereochemistry in carbohydrates
OH at C1 – bottom ring
α glucose
*
All chiral center
diff configuration
↓
Mirror image
α glucose β glucose
OH at C1 – top ring
β glucose
equilibrium bet straight chain – ring form
*
*
*

14. Enantiomers Diastereomers
Same connectivity
Have chiral carbon
Non superimposable
Mirror image each other
Same connectivity
Have chiral carbon
Non superimposable
No Mirror image
diff chemical/physical property
2 chiral centre 22 = 4 stereoisomer
3 chiral centre 23 = 8 stereoisomer
same chemical/physical property
Mirror image
Not Mirror image
diff configuration at one or more
of equivalent stereocenter
chiral centre
not mirror image
same configuration
mirror image
diff configuration
Enantiomer/mirror image
2n n = chiral centre
D fructose L - fructose
Natural occur sugar –D form
Fructose – 3 stereocenter
C5 – chiral center further from C1
– OH on right
- D form
Fructose Isomers
Stereochemistry in carbohydrates
OH at C2 – bottom ring
α fructose
*
All chiral center
diff configuration
↓
Mirror image
α fructose β fructose
OH at C2 – top ring
β fructose
equilibrium bet straight chain – ring form

15. Natural occur sugar –D form
Glucose – 4 stereocenter
C5 – chiral center
– OH on right
- D form
Enantiomer/mirror image
D glucose L - glucose
Glucose Isomers
Stereochemistry in carbohydrates
*All chiral center
diff configuration
↓
Mirror image
equilibrium bet straight chain – ring form
Starch/glycogen - α glucose link together (1-4 α glycosidic link)
Human – have α amylase recognise α glucose - can digest starch
Starch
α glucose α glucose α glucose
(1-4 α glycosidic link)
Cellulose
Cellulose - β glucose link together – (1-4 β glycosidic link)
Cow – have β cellulase recognise β glucose – can digest cellulose
Cellulose – fibre to human – strong long chain - H2 bond bet chain
All OH gp below
(1-4 β glycosidic link)
Β glucose β glucose β glucose β glucose
OH gp alternate
*
*
*

16. Isomers with same Molecular Formula and Structural Formula but diff spatial arrangement
• At least 1 asymmetric / chiral carbon / stereocentre , bonded to 4 diff gp
• NH2CH(R)COOH show optical isomerism
• Optical isomers/mirror images call enantiomers (cannot superimpose on each other)
Optical Isomers
chiral carbon – 4 diff gp
Non superimposable
Non superimposable
click here diastereomers
Optical Isomers
Enantiomers Diastereomers
Same connectivity
Have chiral carbon
Non superimposable
Mirror image each other
Same connectivity
Have chiral carbon
Non superimposable
No Mirror image
diff chemical/physical property
click here diastereomers
same chemical/physical property
Mirror image Not Mirror image
diff configuration at one or more
of equivalent stereocentre
chiral centre
not mirror image
same configuration
mirror image
diff configuration
Video on diastereomers

17. Optical Isomers
Enantiomers Diastereomers
Same connectivity
Have chiral carbon
Non superimposable
Mirror image each other
Same connectivity
Have chiral carbon
Non superimposable
No Mirror image
diff chemical/physical property
2 chiral centre 22 = 4 stereoisomer
3 chiral centre 23 = 8 stereoisomer
same chemical/physical property
Mirror image
Not Mirror image
diff configuration at one or more
of equivalent stereocentre
chiral centre
not mirror image
same configuration
mirror image
diff configuration
Enantiomers and Diastereomers
Diastereomer/NOT mirror image
Can separate by physical/chemical mean
Enantiomer/mirror image
Cant be separated by physical/chemical mean
3 sugar, same structural formula
2n n = chiral centre
All chiral center
diff configuration
↓
Mirror image
Which of the following are enantiomers and diastereomers?
one chiral center
diff configuration
Diastereomer/NOT mirror image
Can separate by physical/chemical mean
two chiral center
diff configuration

18. Optical Isomers
Enantiomers Diastereomers
Same connectivity
Have chiral carbon
Non superimposable
Mirror image each other
Same connectivity
Have chiral carbon
Non superimposable
No Mirror image
diff chemical/physical property
2 chiral centre 22 = 4 stereoisomer
3 chiral centre 23 = 8 stereoisomer
click here to view diastereomers
same chemical/physical property
Mirror image
Not Mirror image
diff configuration at one or more
of equivalent stereocentre
chiral centre
not mirror image
same configuration
mirror image
diff configuration
2, 3 - dibromopentane
Diastereomers
A B C D
Enantiomer/mirror image Enantiomer/mirror image
Diastereomer/NOT mirror image
Enantiomer/mirror image
Diastereomer/NOT mirror image
2n n = chiral centre

19. Stereochemistry in vitamins
RODS
Conjugated protein Rhodopsin
Retina – 2 types light sensitive
RODS (no colour) and CONES (colour)
Light cause photo isomerization
11 cis retinal → all trans retinal (light)
Cis fit into protein opsin
Trans dissociate from protein opsin
Nerve impulse trigger
Rhodopsin made up of
11 cis retinal
↓
Bend
↓
Fit into Opsin
all trans retinal
Straight
Dissociate from Opsin
Light – PHOTO ISOMERIZATION – CIS to TRANS
Opsin (protein) 11 cis retinal
(conjugated
chromophore)
+
visual cycle
Vit A – source of retinal
Lack Vit A – night blindness

20. Write structural formula isomers for C4H9OH, state which isomer show optical isomerism
Butan -1-ol Butan-2-ol 2-methylpropan-2-ol 2-methylpropan-1-ol
All structural isomers
Stereoisomers (Optical Isomers)
Write structural formula of cyclic isomers for C3H4CI2, state type of isomerism
Structural formula
Geometric Isomers
Cis/Tans isomerism
Optical Isomers
Enantiomer, mirror image
Cyclic ring
geometric isomers
CH3-CH2-CH2-CH3
‫׀‬
OH
CH3-CH2-CH-CH3
‫׀‬
OH
CH3
‫׀‬
CH3-C-OH
‫׀‬
CH3
CH3-CH-CH2-OH
‫׀‬
CH3
chiral centre
chiral centre
CI CI
CI
CI
H
HHH
H
HHH CI
CICICI
Trans 1, 2 dichlorocyclopropaneCis 1, 2 dichlorocyclopropane
Stereoisomers (Optical Isomers)
CICI CICI
H HHH
chiral centre chiral centre
* *

21. Optical Isomerism
Which carbon has chiral center?
Draw all stereoisomers CHBr=CHCH(OH)CH3
CHBr=CHCH(OH)CH3
Optical isomersGeometric isomers
Chiral carbon with 4 diff gpDouble bond prevent bond rotation
Cis / Z Trans / E
CH3CH2C*
H(CH3)(CI) CH3C*
H(NH2)COOH CH3C*
H(OH)CH2OH C2H5C*
H(OH)CH2OH
C2H5
H H
‫׀‬ ‫׀‬
C = C
‫׀‬ ‫׀‬
Br CH(OH)CH3
H CH(OH)CH3
‫׀‬ ‫׀‬
C = C
‫׀‬ ‫׀‬
Br H
H
‫׀‬
CHBr=CH-C–CH3
‫׀‬
OH
H
‫׀‬
CH3-C-CH=CHBr
‫׀‬
OH
R (enantiomer) S (enantiomer)
chiral centre
Non chiral centre
NOT mirror image
superimposable
χ
rotate it
They are same. Superimposable
Mirror image
Non superimposable
chiral centre

22. Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenses
http://creativecommons.org/licenses/
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorial
http://lawrencekok.blogspot.com