3.07 optical isomers

• What are the two types of isomers?

  Structural and stereo.
• What is a structural isomer?

  Same molecular formula but different arrangement of atoms.
• What are the three types of structural isomerism?

  Chain, position, functional group.
• What is a chain isomer?

  Isomer with a different arrangement of atoms.
• What is a position isomer?

  Isomer where the functional group differs in location.
• What is a functional group isomer?

  Isomer where a new functional group is made.
• What is stereoisomerism?

  Same structural formula but different arrangement in space.
• Why does stereoisomerism exist?

  Atoms banded around a carbon double bond can't rotate as they are planar and double binds structures are fairly rigid.
• What are the two types of stereoisomerism in alkanes and when does they occur?

  E and Z (geometric), when the double band carbons are bonded to different atoms.
• What is E isomerism?

  When the same group are on opposite sides. Enemies.
• What is Z isomerism?

  When the same group is on the same side. Friendz.
• Explain cohn-ingold-prelogs priority rule.

  Assign priority to groups bonded to the C double bond by Mr (highest Mr = highest priority), then base the isomer name on the two highest priorities).
• What's a key example of the chiral drug problem?

  Thalidomide

  
  

  2 enantiomers - causes birth defects in unborn children whilst the other had useful sedative problems (helped morning sickness)
• How does a racemic mixture form?

  Trigonal Planar Intermediate

  
  

  Attacked from either side

  
  

  With equal probability / to form equal amounts of each enantiomer in the mixture
• How do chemists solve the chiral drug problem?

  Separate the isomers (expensive and difficult)

  
  

  Use the racemic mixture (double dose needed / may have side effects)

  
  

  Design an alternative synthesis for the drug
• What is the chiral drug problem?

  Most biological molecules exact as only 1 enantiomer

  
  

  This means different enantiomers of a drug bind differently to the target receptor.
• Contrast addition and substitution reactions in their formation of enantiomers.

  Addition reactions usually form the two enantiomers in equal proportions.

  
  

  Whereas, substitution reactions only form 1 enantiomer.
• Why are racemic mixtures optically inactive?

  The enantiomers cancel each others effect.
• What is a racemic mixture?

  A mixture which contains equal quantities of each enantiomer.
• What are optical isomers / enantiomers?

  These are two molecules which contain an asymmetric carbon atom and are mirror images of one another. The molecules cannot be superimposed.
• What is the difference in the effect of two enantiomers on plane polarised light?

  They rotate plane polarised in opposite directions.

  
  

  isomers rotates it clockwise.

  
  

  isomers rotate it anti-clockwise.
• What is a chiral carbon atom?

  An asymmetric carbon atom that has 4 different groups attached to it.