ttp://lawrencekok.blogspot.com Prepared by Lawrence Kok Option B Stereoisomers for Protein, Lipids, Carbohydrates, Vitamin A and iodine number for unsaturated fats.
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Prepared by Lawrence Kok
Option B Stereoisomers for Protein, Lipids, Carbohydrates,Vitamin A and iodine number for unsaturated fats.
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
DifferentDifferentDifferent
SimilarSimilar
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
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
EnantiomerMirror image of each
other
EnantiomerMirror 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 IsomerAtom on same
side
Trans IsomerAtom 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
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 clockwiseEnantiomer (S) – rotate anticlock wise
50% 50% 70% 30%
Optically active – Net Rotation clockwise
Non superimposable
Non superimposable
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 direction3. Turn analyzer either clockwise/anticlock wise to give light of max intensity again4. 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 lightOptically 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 samplewhich able to rotate polarized light
2nd polarizer(Analyzer)
Polarizer tube
Rotated clockwise
How Polarimeter works ?
R – inactiveRacemate mix ibuprofen
S – activeRacemate mix ibuprofenIbuprofen (painkiller)
Click here notes isomers
R limonene S limonene
CH3
CH3
CH3
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 – inactiveRacemate mix ibuprofen
S – activeRacemate mix ibuprofenIbuprofen
(painkiller) R limonene S limonene
CH3
CH3
CH3
Stereoisomerism
Mirror image / enantiomersSame chemical/physical propertyexcept rotation of polarized light
Source/smell orange Source/smell
lemon
Mirror image / enantiomersSame chemical/physical propertyexcept rotation of polarized light
R carvone S carvone
Mirror image / enantiomersSame chemical/physical propertyexcept 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!
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 – tastelessSynthesize D amino acid – sweetDue to taste receptor in our body
Chiral carbon
D amino acidEnantiomer(R)
Rotate clockwise
L amino acidEnantiomer(S)
Rotate anticlock wiseLD
Cis IsomerAtom on same
side
Trans IsomerAtom on diff side
Stereochemistry in lipids
Geometric Isomers
Long hydrocarbon fatty acid chain
Saturated (No C = C)
Unsaturated ( C = C)
Fatty acidSaturated, unsaturated and polyunsaturated
Presence cis /trans isomersNaturally fatty acids – cis form
Cis IsomerAtom on same
side
Trans IsomerAtom on diff side
Stereochemistry in lipids
Geometric Isomers
Long hydrocarbon fatty acid chain
Saturated (No C = C)
Unsaturated ( C = C)
Fatty acidSaturated, unsaturated and polyunsaturated
Presence cis /trans isomersNaturally fatty acids – cis form
Cis fatty acidKink/ bend – unable to pack closely
Weaker intermolecular forces attractionVDF lower – m/p lower - liquid
Trans fatty acidStraight chain – close packed togetherStrong 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 formTrans able to pack close together High m/p – solid form more stable to temp/oxiHigh risk – heart attackIncrease level LDL (bad cholesterol)
Polyunsaturated (> 2C = C)
Trans fats (straight)
ConvertH2 Ni catalyst
Cis (bend)
complete hydrogenation
partial hydrogenation
Lipids chemistry
Rancidity of lipids
Condensation – Form triglyceride
+
Hydrolysis – Glycerol and Fatty acids
Hydrolytic rancidity Oxidative rancidity
Presence H2O/heatHydrolysis rxn – (water)- ester link broken
Presence O2/light/enzymesOxidative rxn- react with C=C (unsaturation)
Free radical mechanism
LDL vs HDL
LDLHigh ratio lipid to protein
More lipid/Less proteinCarry lipid/cholesterol to artery
Bad cholesterol
lipid
protein
HDLHigh ratio protein to lipid
More protein/Less lipidCarry cholesterol from artery to liver
Good cholesterol
VS lipid
protein
Stereochemistry in lipids
Presence cis /trans isomersNaturally fatty acids – cis form
Cis fatty acidKink/ bend – unable to pack closely
Weaker intermolecular forces attractionVDF lower – m/p lower - liquid
Good fatty acidMono unsaturated (1 C =C ) Polyunsaturated (> 2C = C)
Omega 3 fatty acid Omega 6 fatty acid
Omega-3 fatty acid reduce blood triglycerideIncrease HDL level - HDL as "good cholesterol" they transport cholesterol out of blood artery walls, and
transport back to liverCholesterol 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
Meltingpoint
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 saturationIodine 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
Stereochemistry in lipids
Fatty acid Molar mass
C =C
bond
Meltingpoint
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 saturationIodine 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 acid100 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 = 253.8Moles 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 oxidizedMore energy when oxidized/combusted
Stereochemistry in lipids
Fatty acid Molar mass
C =C
bond
Meltingpoint
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 = 274274 g I2 – 100 g linoleic acid761.7 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–mol g 126.902g 7.7
1–mol g 278.48g 8.2
:
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
Natural occur sugar –D formGlucose – 4 stereocenterC5 – chiral center further from C1 – OH on right - D form
Enantiomers Diastereomers
Same connectivityHave chiral carbon
Non superimposableMirror image each
other
Same connectivity Have chiral
carbonNon
superimposableNo 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 imagesame 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
***
Enantiomers Diastereomers
Same connectivityHave chiral carbon
Non superimposableMirror image each
other
Same connectivity Have chiral
carbonNon
superimposableNo 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 imagesame configuration
mirror image diff configuration
Enantiomer/mirror image
2n n = chiral centre
D fructose L - fructose
Natural occur sugar –D formFructose – 3 stereocenterC5 – 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
Natural occur sugar –D formGlucose – 4 stereocenterC5 – 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
***
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 connectivityHave chiral carbon
Non superimposableMirror image each
other
Same connectivity Have chiral
carbonNon
superimposableNo 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 imagesame configuration
mirror imagediff configuration
Video on diastereomers
Optical Isomers
Enantiomers Diastereomers
Same connectivityHave chiral carbon
Non superimposableMirror image each
other
Same connectivity Have chiral
carbonNon
superimposableNo 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 imagesame configuration
mirror image diff configuration
Enantiomers and Diastereomers
Diastereomer/NOT mirror imageCan separate by physical/chemical mean
Enantiomer/mirror imageCant 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 imageCan separate by physical/chemical mean
two chiral center diff configuration
Optical Isomers
Enantiomers Diastereomers
Same connectivityHave chiral carbon
Non superimposableMirror image each
other
Same connectivity Have chiral
carbonNon
superimposableNo 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 imagesame 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
Stereochemistry in vitamins
RODS Conjugated protein Rhodopsin
Retina – 2 types light sensitive RODS (no colour) and CONES
(colour)
Light cause photo isomerization11 cis retinal → all trans retinal (light)
Cis fit into protein opsinTrans 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 retinalLack Vit A – night blindness
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 IsomersCis/Tans isomerism
Optical IsomersEnantiomer, 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
H H H
H
H H H CI
CI CI CI
Trans 1, 2 dichlorocyclopropaneCis 1, 2 dichlorocyclopropaneStereoisomers (Optical Isomers)
CI CI CI CI
H H H H
chiral centre
chiral centre
* *
Optical IsomerismWhich carbon has chiral center?
Draw all stereoisomers CHBr=CHCH(OH)CH3
CHBr=CHCH(OH)CH3
Optical isomersGeometric isomers
Chiral carbon with 4 diff gp Double bond prevent bond rotationCis / 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 imagesuperimposable
χrotate it
They are same. Superimposable
Mirror imageNon superimposable
chiral centre
Acknowledgements
Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/
Prepared by Lawrence Kok
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