http://lawrencekok.blogspot.com

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

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com