Diastereomers

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Diastereomers

• Stereoisomers
• same molecular formula, same bonding arrangement,
  different spatial arrangement
• Enantiomers
• two stereoisomers that are nonsuperimposable
  mirror images
• Diastereomers
• stereoisomers that are NOT mirror images

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Diastereomers

• In general, diastereomers fall into two
  categories
• geometric isomers
• cis-trans
• compounds containing two or more asymmetric atoms
  (but not mirror images)

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Fischer Projections

• Fischer Projections are often used to depict
  stereochemistry when more than one asymmetric
  carbon is present.
• Left and Right come toward you.
• Top and Bottom go away from you.

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Fischer Projections

• Rules for using Fischer Projections
• Carbon chain is drawn along the vertical line of
  the Fischer Projection
• C 1 at the top
• asymmetric carbon where the lines cross
• Vertical lines
• bonds going away from you
• Horizontal lines
• bonds coming towards you

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Fischer Projections

• Rules for using Fischer Projections
• Structures can be rotated by 180o only.
• Rotation by 90o is NOT allowed.
• You cannot flip over a Fischer Projection.

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Fischer Projections

• Fischer Projections are useful when
• drawing mirror images
• identifying internal mirror planes of symmetry

s
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Fischer Projections

• Fischer Projections are useful when
• determining if two substances are
  nonsuperimposable mirror images
• remember to follow the rules for using Fischer
  Projections

rotate 180o
superimposable
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Stereochemical Relationships

• On your exam, you must be able to identify the
  relationship between two structures.
• Different compounds that are not isomers
• Same compounds
• Enantiomers
• Diastereomers

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Stereochemical Relationships

• Different compounds, not isomers
• Different molecular formulas
• Structural (constitutional) isomers
• Same molecular formula, different bonding pattern

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Stereochemical Relationships

• Same Compound
• Same molecular formula, same bonding pattern
• All sets of equivalent asymmetric carbons will
  have the same configurations

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Stereochemical Relationships

• Enantiomers
• Same molecular formula, same bonding pattern
• All sets of equivalent asymmetric carbons will
  have the opposite configuration

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Stereochemical Relationships

• Diastereomers
• Same molecular formula, same bonding pattern
• At least one set of equivalent asymmetric carbons
  has the same configuration AND
• At least one set of equivalent asymmetric carbons
  has the opposite configuration

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Stereochemical Relationships

• Example Determine the relationship between the
  following pairs of compounds.

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Identifying All Possible Stereoisomers

• A compound with n asymmetric carbon atoms can
  have a maximum of 2n stereoisomers.

• Example What is the maximum number of
  stereoisomers for each of the following
  compounds?
• 2,3-dibromobutane
• 2,3-dibromo-5-methyloctane

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Identifying All Possible Stereoisomers

• 2,3-dibromobutane only has 3 distinctly different
  stereoisomers

enantiomers
What is the relationship between the compounds
above and below?
s
s
Same compound
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Identifying All Possible Stereoisomers

• Example Draw 3-d structures of all possible
  stereoisomers of 2,3-dichloropentane. Which ones
  are chiral? Name each one. Give the
  stereochemical relationship between them.

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Identifying All Possible Stereoisomers
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Identifying All Possible Stereoisomers
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Review

• Example Is the following compound chiral? Name
  the compound.

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Review

• Example Is the following compound chiral? What
  is the maximum number of stereoisomers possible
  for this compound. Draw one possible
  diastereomer of this compound.