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IB Chemistry on Stereoisomerism, Optical and Geometrical Isomers

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IB Chemistry on Stereoisomerism, Optical, Geometrical Isomers and Polarimeter.

IB Chemistry on Stereoisomerism, Optical, Geometrical Isomers and Polarimeter.

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  • 1. Tutorial on Stereoisomerisms, Optical andGeometrical Isomers. Prepared by Lawrence Kok http://lawrencekok.blogspot.com
  • 2. Isomerism Isomers – Organic molecules with same molecular formula but different arrangement of atoms Hydrocarbon Chain Isomer CH3 -CH –CH2 –CH3 • Different hydrocarbon │ Structural Isomerism chain skeleton OH • Same molecular formula • Different structural formula • Different arrangement of atoms CH3 -CH –CH –CH3 Positional Chain Isomer │ • Different functional OH group position Functional Group Isomer CH3 –CH2–CH2 – O – CH3Two types of Isomerism • Different functional group Cis Isomers Atoms are located on the same side Geometric Isomers Trans Isomers Stereoisomerism Atoms are located on • Same molecular formula the different side • Same structural formula • Different spatial arrangement of atoms Optical Isomers
  • 3. IsomerismIsomers – Organic molecules with same molecular formula but different arrangement of atoms Hydrocarbon Chain Isomer CH3 –CH2 –CH2 –CH3 • Different hydrocarbon │ Structural Isomerism chain skeleton OH • Same molecular formula • Different structural formula • Different arrangement of atoms CH3 –CH2 –CH –CH3 Positional Chain Isomer │ • Different functional OH group position Functional Group Isomer CH3 –CH2–CH2 – O – CH3 • Different functional group Structural Isomerism for C4H9 Hydrocarbon Chain Isomer Positional Chain Isomer Functional Group Isomer • Different hydrocarbon • Different functional • Different functional group chain skeleton group position
  • 4. Isomerism Isomers – Organic molecules with same molecular formula but different arrangement of atoms Hydrocarbon Chain Isomer CH3 –CH2 –CH2 –CH3 • Different hydrocarbon │ Structural Isomerism chain skeleton OH • Same molecular formula • Different structural formula • Different arrangement of atoms CH3 –CH2 –CH –CH3 Positional Chain Isomer │ • Different functional OH group position Functional Group Isomer CH3 –CH2–CH2 – O – CH3 • Different functional group Structural Isomerism for C4H9 Hydrocarbon Chain Isomer Positional Chain Isomer Functional Group Isomer • Different hydrocarbon • Different functional • Different functional group chain skeleton group positionCH3 –CH2 –CH2 –CH3 CH3 - CH – CH2 – OH CH3 –CH2 –CH2 –CH3 CH3 –CH2 –CH –CH3 CH3 –CH2 –CH2 –CH3 CH3 –CH2 – O – CH2 -CH3 │ │ │ │ │ OH CH3 OH OH OH CH3 │ CH3 –CH2–CH2 – O – CH3 CH3 - C – OH │ CH3
  • 5. Isomerism Isomers – Organic molecules with same molecular formula but different arrangement of atoms Stereoisomerism • Same molecular formula • Same structural formula • Different spatial arrangement of atoms Geometric Isomers Vs Optical Isomers Geometric Isomers Optical Isomers• Same chemical properties – Same functional group • Same chemical properties – Same functional group• Different physical properties – Different spatial arrangement • Same physical properties –(Different density, polarity, solubility, melting point/boiling point) (Same density, polarity, solubility, melting point/boiling point) • Can only be differentiated by rotation of plane polarised light by optically active isomers
  • 6. Isomerism Isomers – Organic molecules with same molecular formula but different arrangement of atoms Stereoisomerism • Same molecular formula • Same structural formula • Different spatial arrangement of atoms Geometric Isomers Vs Optical Isomers Geometric Isomers Optical Isomers• Same chemical properties – Same functional group • Same chemical properties – Same functional group• Different physical properties – Different spatial arrangement • Same physical properties –(Different density, polarity, solubility, melting point/boiling point) (Same density, polarity, solubility, melting point/boiling point) • Can only be differentiated by rotation of plane polarised light by optically active isomers Cis Isomers Trans Isomers Enantiomer Enantiomer Atom are located on Atom are located on Mirror image of each other Mirror image of each other the same side the different side CI CI CI H │ │ │ │ C = C C = C │ │ │ │ H H H CI Cis 1, 2 dichloroethene Trans 1, 2 dichloroethene
  • 7. Geometrical Isomerism Geometric Stereoisomerism • Same molecular formula Cis Isomers • Same structural formula Trans IsomersAtoms are located on the same side • Different spatial arrangement of atoms Atoms are located on the different side Requirement for geometrical isomers • Presence of C=C double bond to prevent bond rotation • Presence of ring structure to prevent bond rotation • Carbon atom in double bond must be bonded to different atoms
  • 8. Geometrical Isomerism Geometric Stereoisomerism • Same molecular formula Cis Isomers • Same structural formula Trans Isomers Atoms are located on the same side • Different spatial arrangement of atoms Atoms are located on the different side Requirement for geometrical isomers • Presence of C=C double bond to prevent bond rotation • Presence of ring structure to prevent bond rotation • Carbon atom in double bond must be bonded to different atoms Presence of Double Bond C=C CI –CH=CH –CI CI CI CI H │ │ │ │ C = C C = C │ │ │ │ H H H CI Cis Trans1, 2 dichloroethene 1, 2 dichloroethene
  • 9. Geometrical Isomerism Geometric Stereoisomerism • Same molecular formula Cis Isomers • Same structural formula Trans Isomers Atoms are located on the same side • Different spatial arrangement of atoms Atoms are located on the different side Requirement for geometrical isomers • Presence of C=C double bond to prevent bond rotation • Presence of ring structure to prevent bond rotation • Carbon atom in double bond must be bonded to different atoms Presence of Double Bond C=C Presence of ring structure CI –CH=CH –CI CI CI CI H │ │ │ │ C = C C = C │ │ │ │ H H H CI Cis Trans1, 2 dichloroethene 1, 2 dichloroethene Cis Trans 1, 2 dichlorocyclopropane 1, 2 dichlorocyclopropane
  • 10. Geometrical Isomerism Geometric Stereoisomerism • Same molecular formula Cis Isomers • Same structural formula Trans Isomers Atoms are located on the same side • Different spatial arrangement of atoms Atoms are located on the different side Requirement for geometrical isomers • Presence of C=C double bond to prevent bond rotation • Presence of ring structure to prevent bond rotation • Carbon atom in double bond must be bonded to different atoms Presence of Double Bond C=C Presence of ring structure Carbon atom bonded to different atoms CI –CH=CH –CI X X H CI H CI CI CI CI H CI CI CI H │ │ │ │ │ │ │ │ │ │ │ │ C = C C = C C = C C = C C = C C = C │ │ │ │ │ │ │ │ │ │ │ │ H H H H H H H CI H H H CI Cis Trans Cis Trans1, 2 dichloroethene 1, 2 dichloroethene Cis Trans NO Cis/Trans 1, 2 dichloroethene 1, 2 dichloroethene 1, 2 dichlorocyclopropane 1, 2 dichlorocyclopropane Geometric Isomers • Same chemical properties – Same functional group • Different physical properties – Different spatial arrangement (Different density, polarity, solubility, melting point /boiling point)
  • 11. Optical IsomerismIsomers having same Molecular Formula and Structural Formula but different spatial arrangement• At least 1 asymmetric / chiral carbon which is bonded to 4 different groups
  • 12. Optical IsomerismIsomers having same Molecular Formula and Structural Formula but different spatial arrangement• At least 1 asymmetric / chiral carbon which is bonded to 4 different groups• NH2CH(R)COOH show optical isomerism• Two optical isomers/mirror images are called enantiomers (cannot superimpose on each other)• Have similar physical and chemical properties except for the effect on rotation of plane of polarised light
  • 13. Optical IsomerismIsomers having same Molecular Formula and Structural Formula but different spatial arrangement• At least 1 asymmetric / chiral carbon which is bonded to 4 different groups• NH2CH(R)COOH show optical isomerism• Two optical isomers/mirror images are called enantiomers (cannot superimpose on each other)• Have similar physical and chemical properties except for the effect on rotation of plane of polarised light• Optically active – enantiomers able to rotate plane polarised light to one direction (clockwise/anticlockwise) or Rotate to right Rotate to left• Optically inactive – enantiomers present in equal amount (equimolar) – racemic mixture and rotation cancel out each other rotation cancel out each other http://chemwiki.ucdavis.edu/Organic_Chemistry/Chirality/Optical_Activity
  • 14. Optical Isomerism• Butan -2-ol (CH3CH(OH)C2H5) has asymmetrical chiral carbon• Enantiomers are mirror image and non superimposable on each other•Two enantiomers both rotate plane of polarised light in different directions
  • 15. Optical Isomerism • Butan -2-ol (CH3CH(OH)C2H5) has asymmetrical chiral carbon • Enantiomers are mirror image and non superimposable on each other •Two enantiomers both rotate plane of polarised light in different directions How polarimeter detects optical isomers ?1. Light pass through 1st polariser – plane polarised light produced
  • 16. Optical Isomerism • Butan -2-ol (CH3CH(OH)C2H5) has asymmetrical chiral carbon • Enantiomers are mirror image and non superimposable on each other •Two enantiomers both rotate plane of polarised light in different directions How polarimeter detects optical isomers ?1. Light pass through 1st polariser – plane polarised light produced2. Sample introduced into sample tube. If sample is optically active – will rotated plane of polarised light to one direction
  • 17. Optical Isomerism • Butan -2-ol (CH3CH(OH)C2H5) has asymmetrical chiral carbon • Enantiomers are mirror image and non superimposable on each other •Two enantiomers both rotate plane of polarised light in different directions How polarimeter detects optical isomers ?1. Light pass through 1st polariser – plane polarised light produced2. Sample introduced into sample tube. If sample is optically active – will rotated plane of polarised light to one direction3. Turn the analyzer either clockwise/anticlock wise to give light of maximum intensity again4. If one enantiomer rotates light 120 clockwise – Analyzer will need to be rotated anticlock wise 120 – sample is said to be optically active Optically active enantiomer
  • 18. Optical Isomerism • Butan -2-ol (CH3CH(OH)C2H5) has asymmetrical chiral carbon • Enantiomers are mirror image and non superimposable on each other •Two enantiomers both rotate plane of polarised light in different directions How polarimeter detects optical isomers ?1. Light pass through 1st polariser – plane polarised light produced2. Sample introduced into sample tube. If sample is optically active – will rotated plane of polarised light to one direction3. Turn the analyzer either clockwise/anticlock wise to give light of maximum intensity again4. If one enantiomer rotates light 120 clockwise – Analyzer will need to be rotated anticlock wise 120 – sample is said to be optically active Optically active enantiomer5. If one enantiomer rotates light 120 clockwise – Another enantiomer rotates light anticlock wise 120 – sample is said to be optically inactive Optically inactive enantiomer cancel each other rotation6. Racemic Mixture = enantiomers present in equal amount (equimolar) and cancel each other rotation
  • 19. Optical Isomerism • Optical activity is the ability of solution to rotate the plane of polarised light Substance are said to be optically active – able to rotate plane of polarised light Polarimeter • Two polarising filters that can be rotated to each other, separated by a compartment in which the plane polarise light passes through a liquid • Plane of polarised light – oscillation of wave is restricted to one plane – vertically by passing through a polarised filter • Optically active isomers – able to rotate plane of polarised light to one direction – presence of asymmetrical/chiral carbon bonded to 4 different groups • An equimolar mixture of enantiomers is called racemic mixture – Racemic mixture is optically inactiveProducts/Drugs from natural sources/catalysed by enzyme Products synthesised chemically• gives only one pure optically active enantiomer • gives two enantiomers in equal amount or racemic mixture• chiral and found in single enantiomers – optically active • optically inactive rotation cancel out each other = Optically active Optically inactive
  • 20. Questions on Isomerism Write the structural formula for all isomers for C4H9OH and state which isomer shows optical isomerismWrite the structural formula of cyclic isomers for C3H4CI2, and state the type of isomerism
  • 21. Questions on Isomerism Write the structural formula for all isomers for C4H9OH and state which isomer shows optical isomerism All structural isomers CH3 CH3 –CH2 –CH2 –CH2 CH3 –CH –CH2 –CH3 CH3 - CH – CH2 – OH │ │ │ │ CH3 - C – OH OH OH CH3 │ CH3 Butan -1-ol Butan-2-ol 2-methylpropan-1-ol 2-methylpropan-2-olWrite the structural formula of cyclic isomers for C3H4CI2, and state the type of isomerism All structural isomers Both are Structural formula
  • 22. Questions on Isomerism Write the structural formula for all isomers for C4H9OH and state which isomer shows optical isomerism All structural isomers CH3 CH3 –CH2 –CH2 –CH2 CH3 –CH –CH2 –CH3 CH3 - CH – CH2 – OH │ │ │ │ CH3 - C – OH OH OH CH3 │ CH3 Butan -1-ol Butan-2-ol 2-methylpropan-1-ol 2-methylpropan-2-ol Stereoisomers Optical isomersWrite the structural formula of cyclic isomers for C3H4CI2, and state the type of isomerism All structural isomers Cyclic ring – geometric isomers Both are Structural formula Chiral center – optical isomers Stereoisomers Optical Isomers Geometric Isomers Enantiomers, mirror image Cis/Tans isomerism
  • 23. Questions on Isomerism Write the structural formula for all isomers for C4H9OH and state which isomer shows optical isomerism All structural isomers CH3 CH3 –CH2 –CH2 –CH2 CH3 –CH –CH2 –CH3 CH3 - CH – CH2 – OH │ │ │ │ CH3 - C – OH OH OH CH3 │ CH3 Butan -1-ol Butan-2-ol 2-methylpropan-1-ol 2-methylpropan-2-ol Stereoisomers Optical isomersWrite the structural formula of cyclic isomers for C3H4CI2, and state the type of isomerism All structural isomers Cyclic ring – geometric isomers Both are Structural formula Chiral center – optical isomers Stereoisomers Optical Isomers Geometric Isomers Enantiomers, mirror image Cis/Tans isomerism
  • 24. Questions on IsomerismWrite the structural formula for all isomers for C4H9OH and state which isomer shows optical isomerism All structural isomers CH3 –CH2 –CH2 –CH2 CH3 –CH –CH2 –CH3 CH3 - CH – CH2 – OH CH3 │ │ │ │ OH OH CH3 CH3 - C – OH │ Butan -1-ol Butan -2-ol 2-methylpropan-1-ol CH3 2-methylpropan-2-olWhich of the following pairs are stereoisomers?A CH3 CH3 CH3 CI B CH3 Br CH3 H C H H │ │ │ │ │ │ │ │ │ │ C = C C = C C = C C = C CH3 - C – COOH HOOC - C – CH3 │ │ │ │ │ │ │ │ │ │ CI CI CI CH3 H CI Br CI NH2 NH2
  • 25. Questions on IsomerismWrite the structural formula for all isomers for C4H9OH and state which isomer shows optical isomerism All structural isomers CH3 –CH2 –CH2 –CH2 CH3 –CH –CH2 –CH3 CH3 - CH – CH2 – OH CH3 │ │ │ │ OH OH CH3 CH3 - C – OH √ │ Butan -1-ol Butan -2-ol 2-methylpropan-1-ol CH3 2-methylpropan-2-ol Stereoisomers Optical isomersWhich of the following pairs are stereoisomers?A CH3 CH3 CH3 CI B CH3 Br CH3 H C H H │ │ │ │ │ │ │ │ │ │ C = C C = C C = C C = C CH3 - C – COOH HOOC - C – CH3 │ │ │ │ │ │ │ │ │ │ CI CI CI CH3 H CI Br CI NH2 NH2 √ √ Geometrical isomers Structural isomers Optical isomers (Stereoisomers) X (Stereoisomers)
  • 26. Optical IsomerismWhich of the carbon has a chiral center?CH3 CH2 C*H(CI) CH3 C*H(NH2)COOH CH3C*H(OH)CH2OH H3CH2C*H(OH)CH2OH │ CH3Draw all stereoisomers for CHBr =CHCH(OH)CH3 CHBr = CH-CH(OH)CH3
  • 27. Optical IsomerismWhich of the carbon has a chiral center?CH3 CH2 C*H(CI) CH3 C*H(NH2)COOH CH3C*H(OH)CH2OH H3CH2C*H(OH)CH2OH │ CH3Draw all stereoisomers for CHBr =CHCH(OH)CH3 CHBr = CH-CH(OH)CH3 Geometric isomers Optical isomers Cis Trans Enantiomer Enantiomer H H H CH(OH)CH3 H H │ │ │ │ │ │ C= C C= C CHBr = CH - C – CH3 CH3 - C – CH=CHBr │ │ │ │ │ │ Br CH(OH)CH3 Br H OH OH
  • 28. Optical IsomerismWhich of the carbon has a chiral center?CH3 CH2 C*H(CI) CH3 C*H(NH2)COOH CH3C*H(OH)CH2OH H3CH2C*H(OH)CH2OH │ CH3Draw all stereoisomers for CHBr =CHCH(OH)CH3 CHBr = CH-CH(OH)CH3 Geometric isomers Optical isomers Cis Trans Enantiomer Enantiomer H H H CH(OH)CH3 H H │ │ │ │ │ │ C= C C= C CHBr = CH - C – CH3 CH3 - C – CH=CHBr │ │ │ │ │ │ Br CH(OH)CH3 Br H OH OH Chiral carbon with 4 different groups Double bond prevent bond rotation
  • 29. Questions on Structural and Geometrical Isomerism Draw the structural formula of isomers having MF C2H2CI2, and state the type of isomerism C2 H2 CI2Draw the structural formula of cyclic isomers having MF C3H4CI2, and state the type of isomerism C3H4CI2
  • 30. Questions on Structural and Geometrical Isomerism Draw the structural formula of isomers having MF C2H2CI2, and state the type of isomerism C2 H2 CI2 CI H H H │ │ Both are Structural formula │ │ C = C C = C │ │ │ │ CI H CI CIDraw the structural formula of cyclic isomers having MF C3H4CI2, and state the type of isomerism C3H4CI2 Both are Structural formula
  • 31. Questions on Structural and Geometrical Isomerism Draw the structural formula of isomers having MF C2H2CI2, and state the type of isomerism C2 H2 CI2 CI H H H │ │ Both are Structural formula │ │ C = C C = C │ │ │ │ CI H CI CI H H H CI │ │ Geometric Isomers │ │ C = C Cis/Tans isomerism C = C │ │ │ │ CI CI CI H Cis TransDraw the structural formula of cyclic isomers having MF C3H4CI2, and state the type of isomerism C3H4CI2 Both are Structural formula Geometric Isomers Cis/Tans isomerism Trans Cis
  • 32. Questions on Structural and Geometrical IsomerismWhich of the following exhibit cis/trans isomerism ? A Br H B CH3 CH3 C H CH3 │ │ │ │ │ │ C = C C = C C = C │ │ │ │ │ │ Br H H H CI CI A CH3CH=CH-CH3 B CH3CH=CH2 C CH(CI)=CH(CI)-CH3Which of the following is an structural isomer of CH3COCH2CH3? A CH2 = CH- CH-CH3 B CH3 –CH2-CH2-CH C CH3 –CH2- O- CH2-CH3 │ ║ OH ODraw the geometrical isomer for the following CH3CH=CHCH2CH3 F-CH = CH-F
  • 33. Questions on Structural and Geometrical IsomerismWhich of the following exhibit cis/trans isomerism ? A Br H B CH3 CH3 C H CH3 │ │ │ │ │ │ C = C C = C C = C │ │ │ │ │ │ Br H H H CI CI X Same atoms on carbon √ √ A CH3CH=CH-CH3 B CH3CH=CH2 C CH(CI)=CH(CI)-CH3 √ X Same atoms on carbon √Which of the following is an structural isomer of CH3COCH2CH3? A CH2 = CH- CH-CH3 B CH3 –CH2-CH2-CH C CH3 –CH2- O- CH2-CH3 │ ║ OH O X √ √Draw the geometrical isomer for the following CH3CH=CHCH2CH3 F-CH = CH-F H H CH3 H F F F H │ │ │ │ │ │ │ │ C = C C = C C = C C = C │ │ │ │ │ │ │ │ CH3 CH2CH3 H CH2CH3 H H H F Cis pent-2-ene Trans pent-2-ene Cis 1, 2 difluoroethene Trans 1, 2 difluoroethene
  • 34. AcknowledgementsThanks to source of pictures and video used in this presentationThanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/Prepared by Lawrence KokCheck out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com