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Absolute & relative configuration

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1. Relative configuration compares the arrangement of atoms in space of one compound to another, while absolute configuration precisely describes the arrangement of atoms in space. 2. Cahn-Ingold-Prelog rules were developed in the 1950s to determine absolute configuration, assigning R or S based on the atomic priorities and spatial arrangement of groups around chiral carbons. 3. To determine absolute configuration using Cahn-Ingold-Prelog rules, groups attached to a chiral carbon are ranked by priority and the molecule is oriented such that the lowest priority group is in the back. Clockwise arrangement is labeled R and counterclockwise is S.

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Relative & Absolute Configuration DR. R. SRINIVASAN DEPT OF PHARMACEUTICAL CHEMISTRY PALLAVAN PHARMACY COLLEGE
Configuration Arrangement of atoms or gps of atoms around the asymmetric centre 3 difference conventions are: D&L, d&l and +&- 2 are same used to indicate the sign of rotation of 2 enantiomers Relative configuration(D & L) compares the arrangement of atoms in space of one compound with those of another. Absolute configuration is the precise arrangement of atoms in space. There is no significance difference between sign of rotation & configuration of an enantiomers because of a compound and derivative have differences in sign of rotations eg. Lactic acid
Relative configuration compares the arrangement of atoms in space of one compound with those of another until the 1950s, all configurations were relative Absolute configuration(actual arrangement of atom in space) is the precise arrangement of atoms in space. we can now determine the absolute configuration of almost any compound Configuration
Relative configuration Any compd prep from or converted into D glyceraldehyde and prep or converted into Lglyceraldehyde are called relative configuration eg. D-glyceraldehyde to D Glyceric acid
No bonds are made or broken at the chiral carbon in this experiment. Therefore, when (+) d-3-buten-2-ol and (+) d -2-butanol have the same sign of rotation, the arrangement of atoms in space at the chiral carbon atom is analogous. The twohave the same relative configuration. CH3CHCH2CH3 OH Pd [a] + 33.2属 [a] + 13.5属 Relative configuration CH3CHCH OH CH2
Not all compounds that have the same relative configuration have the same sign of rotation. No bonds are made or broken at the chiral carbon in the reaction shown, so the relative positions of the atoms are the same. Yet the sign of rotation can change. CH3CH2CHCH2Br CH3 HBr [a] -5.8属 [a] + 4.0属 Relative configuration CH3CH2CHCH2OH CH3
Absolute configuration Clears the basic defects of D&L(relative configuration)were over come when we study in structure of more than one asymmetric C atom. However it is overcome by Cahn Ingold & Prelog (1956, 1964) which is based on three dimensional formula
Three imp features of absolute configuration (R&S system Nomenclature) are: 1. Four different group attached to the asymmetric carbon atom or atoms are arranged in a priority sequence in accordance to the sequences rules After assigning the priorities of the 4 group or atoms attached to chiral carbon the molecules is imagined to be a position where the atom or group of lowest i.e., arrangement towards clockwise direction is specified as R & anticlockwise direction is R 2. R rectus(latin) for right S-sinister left used as D & L series
3. When the molecule is more than one asymmetric centre the procedure is applied to each for explain the of compound towards clockwise R configuration and anticlockwise S configuration
Naming from the Perspective Formula 1 2 3 4 1. Rank the groups bonded to the asymmetric carbon 2. If the group (or atom) with the lowest priority is bonded by hatched wedge,
3. If necessary, rotate the molecule so that the lowest priority group (or atom) is bonded by a hatched wedge 4.
HH3C H H chiral carbon in a ring R CH2C=C > CH2CH2 > CH3 > H
Rules for Fischer projections Arrange the molecule so that horizontal bonds at chiral carbon point toward you and vertical bonds point away from you. Br Cl F H
Rules for Fischer projections Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back. Br Cl F H
Rules for Fischer projections Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back. Br Cl F H
SEQUENCE RULE: 4 RULES ARE GOVERN THE ARRANGMENT OF 4 DIFFERENT GROUP AROUND AN ASYMMETRIC C ATOM RULE 1: In case all the four atoms directly attached to the asymmetric carbon atom are different from one another, sequence of priorities is determined by atomic numbers The atoms of higher molecular weight higher priority and lower molecular weight the last priority
Rule 2: If the two atoms directly attached to asymmetric centre having same atomic number the priority may be determined by comparing the next atom and so on
Rule 3: A double or triple bonded atom X is equivalent to two or less such atom thus the priority of order is aldehyde or CooH gp or OH gp
Absolute & relative configuration
Rule 4: In case of geometrical stereo isomeric group the cis gp precedes trans gp similarly isomer R precedes S gp In case of pseudosymmetric centre the symbol R & S replaced r & s
Absolute & relative configuration

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Absolute & relative configuration

  • 1. Relative & Absolute Configuration DR. R. SRINIVASAN DEPT OF PHARMACEUTICAL CHEMISTRY PALLAVAN PHARMACY COLLEGE
  • 2. Configuration Arrangement of atoms or gps of atoms around the asymmetric centre 3 difference conventions are: D&L, d&l and +&- 2 are same used to indicate the sign of rotation of 2 enantiomers Relative configuration(D & L) compares the arrangement of atoms in space of one compound with those of another. Absolute configuration is the precise arrangement of atoms in space. There is no significance difference between sign of rotation & configuration of an enantiomers because of a compound and derivative have differences in sign of rotations eg. Lactic acid
  • 3. Relative configuration compares the arrangement of atoms in space of one compound with those of another until the 1950s, all configurations were relative Absolute configuration(actual arrangement of atom in space) is the precise arrangement of atoms in space. we can now determine the absolute configuration of almost any compound Configuration
  • 4. Relative configuration Any compd prep from or converted into D glyceraldehyde and prep or converted into Lglyceraldehyde are called relative configuration eg. D-glyceraldehyde to D Glyceric acid
  • 5. No bonds are made or broken at the chiral carbon in this experiment. Therefore, when (+) d-3-buten-2-ol and (+) d -2-butanol have the same sign of rotation, the arrangement of atoms in space at the chiral carbon atom is analogous. The twohave the same relative configuration. CH3CHCH2CH3 OH Pd [a] + 33.2属 [a] + 13.5属 Relative configuration CH3CHCH OH CH2
  • 6. Not all compounds that have the same relative configuration have the same sign of rotation. No bonds are made or broken at the chiral carbon in the reaction shown, so the relative positions of the atoms are the same. Yet the sign of rotation can change. CH3CH2CHCH2Br CH3 HBr [a] -5.8属 [a] + 4.0属 Relative configuration CH3CH2CHCH2OH CH3
  • 7. Absolute configuration Clears the basic defects of D&L(relative configuration)were over come when we study in structure of more than one asymmetric C atom. However it is overcome by Cahn Ingold & Prelog (1956, 1964) which is based on three dimensional formula
  • 8. Three imp features of absolute configuration (R&S system Nomenclature) are: 1. Four different group attached to the asymmetric carbon atom or atoms are arranged in a priority sequence in accordance to the sequences rules After assigning the priorities of the 4 group or atoms attached to chiral carbon the molecules is imagined to be a position where the atom or group of lowest i.e., arrangement towards clockwise direction is specified as R & anticlockwise direction is R 2. R rectus(latin) for right S-sinister left used as D & L series
  • 9. 3. When the molecule is more than one asymmetric centre the procedure is applied to each for explain the of compound towards clockwise R configuration and anticlockwise S configuration
  • 10. Naming from the Perspective Formula 1 2 3 4 1. Rank the groups bonded to the asymmetric carbon 2. If the group (or atom) with the lowest priority is bonded by hatched wedge,
  • 11. 3. If necessary, rotate the molecule so that the lowest priority group (or atom) is bonded by a hatched wedge 4.
  • 12. HH3C H H chiral carbon in a ring R CH2C=C > CH2CH2 > CH3 > H
  • 13. Rules for Fischer projections Arrange the molecule so that horizontal bonds at chiral carbon point toward you and vertical bonds point away from you. Br Cl F H
  • 14. Rules for Fischer projections Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back. Br Cl F H
  • 15. Rules for Fischer projections Projection of molecule on page is a cross. When represented this way it is understood that horizontal bonds project outward, vertical bonds are back. Br Cl F H
  • 16. SEQUENCE RULE: 4 RULES ARE GOVERN THE ARRANGMENT OF 4 DIFFERENT GROUP AROUND AN ASYMMETRIC C ATOM RULE 1: In case all the four atoms directly attached to the asymmetric carbon atom are different from one another, sequence of priorities is determined by atomic numbers The atoms of higher molecular weight higher priority and lower molecular weight the last priority
  • 17. Rule 2: If the two atoms directly attached to asymmetric centre having same atomic number the priority may be determined by comparing the next atom and so on
  • 18. Rule 3: A double or triple bonded atom X is equivalent to two or less such atom thus the priority of order is aldehyde or CooH gp or OH gp
  • 20. Rule 4: In case of geometrical stereo isomeric group the cis gp precedes trans gp similarly isomer R precedes S gp In case of pseudosymmetric centre the symbol R & S replaced r & s