OPTICAL ISOMERISM
• All molecules have a mirror image –  but in most of the cases image and  object are the same molecule.        H         ...
• For some molecules the mirror image  is a different molecule (the mirror  image is non-superimposable).           OH    ...
• Left and right hands are an example  of non-superimposable mirror images.
• This usually happens when a molecule  contains a C atom with four different  groups attached (chiral / asymmetric C).• S...
• The optical isomers are called  enantiomers.• These are distinguished by +/-, D/L or  more correctly Rectus-right/Sinist...
TASK Which of the following     molecules are optically active?1)   propan-2-ol      •   butanone2)   2-chlorobutane   •  ...
propan-2-ol   CH3   CH   CH3                    OH       NOT OPTICALLY ACTIVE
2-chlorobutane   CH3    CH     CH2   CH3                        Cl       CH2CH3                  CH2CH3       C           ...
1-chlorobutane   CH2   CH2   CH2   CH3                 Cl      NOT OPTICALLY ACTIVE
3-methylhexane    CH3 CH2 CH CH2 CH2 CH3                         CH3    CH2CH2CH3                  CH2CH 2CH 3    C       ...
butanone          O            CH3   C   CH2   CH3      NOT OPTICALLY ACTIVE
propan-2-ol   CH3   CH   CH3                    OH      NOT OPTICALLY ACTIVE
2-methylbutanoic acid               CH3   O                        CH3   CH2   CH    C   OH       CH2CH3                  ...
butan-2-ol                     OH                   CH3   CH2   CH       CH3        CH2CH3                      CH2CH3    ...
1-chloro-3-methylpentane            CH3         Cl                       CH3    CH2   CH    CH2   CH2       CH2CH3        ...
• Molecules that are optical isomers are  called enantiomers.• Enantiomers have identical chemical  and physical propertie...
1-The wave vibrations are perpendicular      to the direction of travel of the wave.         normal light                 ...
• Optical isomers rotate the plane of    plane polarised light.     (-)-enantiomer           (+)-enantiomer        (±)-rac...
2- Chiral molecules often react  differently with other chiral molecules.• This is like the idea that a right hand  does n...
• For example, most amino acids (and  so proteins) are chiral, along with  many other molecules.• The human body can consu...
• Many drugs are optically active, with  one enantiomer only having the  beneficial effect.• In the case of some drugs, th...
• In the 1960’s thalidomide was given  to pregnant women to reduce the  effects of morning sickness.• This led to many dis...
O         NH            O                       O           NH          O                            O             O    H2...
CH3                       CH3   O                                           O       H         C   CH2   H2C   C         H ...
CH3                    CH3CH2   C         H            H         C   CH2          CH3                    H3C S limonene (l...
Optical isomers
Optical isomers
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Optical isomers

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Optical isomers

  1. 1. OPTICAL ISOMERISM
  2. 2. • All molecules have a mirror image – but in most of the cases image and object are the same molecule. H H C C H H H H F F fluoromethane
  3. 3. • For some molecules the mirror image is a different molecule (the mirror image is non-superimposable). OH OH C C COOH HOOC H H3C H CH3 (-) lactic acid (+) lactic acid in sour milk in muscles
  4. 4. • Left and right hands are an example of non-superimposable mirror images.
  5. 5. • This usually happens when a molecule contains a C atom with four different groups attached (chiral / asymmetric C).• Such molecules are said to be chiral or optically active. a a C C d d b c c b
  6. 6. • The optical isomers are called enantiomers.• These are distinguished by +/-, D/L or more correctly Rectus-right/Sinister-left.• A 50/50 mixture of the two enantiomers is called a racemic mixture or a racemate.
  7. 7. TASK Which of the following molecules are optically active?1) propan-2-ol • butanone2) 2-chlorobutane • 2-methylbutanoic acid3) 1-chlorobutane • butan-2-ol4) 3-methylhexane • 1-chloro-3-methylpentane
  8. 8. propan-2-ol CH3 CH CH3 OH NOT OPTICALLY ACTIVE
  9. 9. 2-chlorobutane CH3 CH CH2 CH3 Cl CH2CH3 CH2CH3 C C CH3 H3C H H Cl Cl OPTICALLY ACTIVE
  10. 10. 1-chlorobutane CH2 CH2 CH2 CH3 Cl NOT OPTICALLY ACTIVE
  11. 11. 3-methylhexane CH3 CH2 CH CH2 CH2 CH3 CH3 CH2CH2CH3 CH2CH 2CH 3 C C CH3 CH3H H CH2CH 3 CH3CH2 OPTICALLY ACTIVE
  12. 12. butanone O CH3 C CH2 CH3 NOT OPTICALLY ACTIVE
  13. 13. propan-2-ol CH3 CH CH3 OH NOT OPTICALLY ACTIVE
  14. 14. 2-methylbutanoic acid CH3 O CH3 CH2 CH C OH CH2CH3 CH2CH3 C C H HCH3 CH3 COOH HOOC OPTICALLY ACTIVE
  15. 15. butan-2-ol OH CH3 CH2 CH CH3 CH2CH3 CH2CH3 C C H HCH3 CH3 OH HO OPTICALLY ACTIVE
  16. 16. 1-chloro-3-methylpentane CH3 Cl CH3 CH2 CH CH2 CH2 CH2CH3 CH2CH3 C C H HCH3 CH3 CH2CH2Cl CH2ClCH2 OPTICALLY ACTIVE
  17. 17. • Molecules that are optical isomers are called enantiomers.• Enantiomers have identical chemical and physical properties, except: • Their effect on plane polarised light; • Their reaction with other chiral molecules
  18. 18. 1-The wave vibrations are perpendicular to the direction of travel of the wave. normal light plane-polarised light plane-polarised light after(waves vibrate in all directions) (vibrates in only one direction) clockwise rotation
  19. 19. • Optical isomers rotate the plane of plane polarised light. (-)-enantiomer (+)-enantiomer (±)-racemate(anticlockwise rotation) (clockwise rotation) (no overall effect)
  20. 20. 2- Chiral molecules often react differently with other chiral molecules.• This is like the idea that a right hand does not fit a left handed glove – the molecule must be the correct shape to fit the molecule it is reacting with.• Many natural molecules are chiral and most natural reactions are affected by optical isomerism.
  21. 21. • For example, most amino acids (and so proteins) are chiral, along with many other molecules.• The human body can consume amino acids that rotate polarised light to the left.
  22. 22. • Many drugs are optically active, with one enantiomer only having the beneficial effect.• In the case of some drugs, the other enantiomer can even be harmful, e.g. thalidomide.
  23. 23. • In the 1960’s thalidomide was given to pregnant women to reduce the effects of morning sickness.• This led to many disabilities in babies and early deaths in many cases.
  24. 24. O NH O O NH O O O H2C C C H2C CH2 N N CH2 H H O OS thalidomide (effective drug) R thalidomide (dangerous drug) The body racemises each enantiomer, so even pure S isdangerous as it converts to R in the body.
  25. 25. CH3 CH3 O O H C CH2 H2C C H H3C CH3S carvone (caraway seed) R carvone (spearmint)
  26. 26. CH3 CH3CH2 C H H C CH2 CH3 H3C S limonene (lemons) R limonene (oranges)
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