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Chapter 51 Stereochemistry: Chapter 5 The Arrangement of Atoms in Space; The Stereochemistry of Addition Reactions.

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Presentation on theme: "Chapter 51 Stereochemistry: Chapter 5 The Arrangement of Atoms in Space; The Stereochemistry of Addition Reactions."— Presentation transcript:

1 Chapter 51 Stereochemistry: Chapter 5 The Arrangement of Atoms in Space; The Stereochemistry of Addition Reactions

2 Chapter 52 Contents of Chapter 5 Conformational and Configurational Isomers Chirality Centers, Enantiomers Optical Rotation, Optical Purity Isomers with More Than One Chirality Center Separation of Enantiomers Reactions of Chiral Compounds Absolute Configurations Stereochemistry of Reactions

3 Chapter 53 Kinds of Isomers

4 Chapter 54 Conformational Isomers

5 Chapter 55 Configurational Isomers: Cis-Trans Diastereomers

6 Chapter 56 Isomers with One Chirality Center A chirality center arises when four different substituents are bonded to a carbon Only two isomers are possible, an R isomer and an S isomer.

7 Chapter 57 Chirality R and S enantiomers are mirror images of each other, just as your right hand is the mirror image of your left hand

8 Chapter 58 Chirality Any object that has a plane or point of symmetry is achiral (not chiral).

9 Chapter 59 Examples chiral achiral

10 Chapter 510 Mirror Trick Whenever two structures can be positioned around a symmetry plane if they aren’t identical they’re enantiomers.

11 Chapter 511 Drawing Enantiomers Fischer Projections N and S are down into plane, E and W are up out of plane of page or screen.

12 Chapter 512 Naming Enantiomers: The R,S System of Nomenclature Rank groups by atomic number of the atom bonded to the chirality center. Use the same system that was used for the E and Z isomers of alkenes

13 Chapter Orient molecule so that group (or atom) of lowest priority is directed into plane. 3.Draw a curve from group of highest priority through the group of second priority to group of third priority Naming Enantiomers: The R,S System of Nomenclature

14 Chapter 514 Naming Enantiomers: The R,S System of Nomenclature R (Latin rectus) = right turn S (Latin sinister) = left turn (S)-2-bromobutane

15 Chapter 515  If for any reason you ever wish a group were in a different position simply swap it with another group.  Swap simply reverses the chirality. R for switched compound implies S for actual compound Swap Trick

16 Chapter 516 If the low priority group in figure points up rather than down simply draw circular arrow and reverse chirality. Low Priority Group Up Trick R for reversed chirality implies S for actual chirality

17 Chapter 517  If low priority group on vertical line (into plane) draw normal rotating arrow.  If low priority group on horizontal line draw rotating arrow and reverse the R or S result.  Rule of thumb: If group 4 is Vertical, Very true. If group 4 is Horizontal, Horribly wrong. (R)-2-bromobutane Fischer Tricks (S)-2-bromobutane

18 Chapter 518  90º rotation reverses all chiralities.  180º rotation maintains all chiralities. Fischer Tricks

19 Chapter 519  Can rotate 3 groups either CW or CCW without changing configuration  If 3 grps have same rel CW or CCW sequence C’s same Multi-Carbon Fischer Trick

20 Chapter 520  For front C swap low priority group to back C  If swap was necessary curved arrow now gives reversed chirality; otherwise correct Newman Projections

21 Chapter 521  For back C swap low priority group to front C  If swap was necessary curved arrow now gives correct chirality; otherwise reversed Newman Projections

22 Chapter 522 Compounds with More Than One Chirality Center Two Pairs of Similar Groups

23 Chapter 523 Compounds with More Than One Chirality Center Three Pairs of Similar Groups

24 Chapter 524 Meso Compounds

25 Chapter 525 Drill on Meso Compounds Problem 27 Does the following compound have a stereoisomer that is a meso compound? Plane of symmetry Meso form possible

26 Chapter 526 Topology of Stereoisomers With Two Chiral Centers

27 Chapter 527 R,S System for Isomers with More Than One Chirality Center Compound is (2S,3R)-3-bromo-2-butanol

28 Chapter 528 R,S System for isomers with more than one Chirality Center Compound is (2S,3R)-3-bromo-2-butanol

29 Chapter 529 Relative and Absolute Configurations (–) amphetamine is known to have the R- configuration Therefore the (+) form has S configuration

30 Chapter 530 Separation of Enantiomers Racemic lactic acid can be reacted with a naturally occurring chiral base, such as morphine or strychnine The product is a pair of diastereomers Properties of diastereomers are sufficiently different from each other to allow separation After separation, each diastereomer can be reacted with hydrochloric acid, yielding an optically pure R or S acid

31 Chapter 531 Enantiotopic, Diastereotopic, and Homotopic Hydrogens

32 Chapter 532 Enantiotopic, Diastereotopic, and Homotopic Hydrogens

33 Chapter 533 Regioselective, Stereoselective, and Stereospecific Reactions A regioselective reaction is one in which multiple constitutional isomers possible, but more of some formed than others.

34 Chapter 534 Regioselective, Stereoselective, and Stereospecific Reactions A stereoselective reaction can produce multiple stereoisomers theoretically, but more of some produced than others.

35 Chapter 535 Regioselective, Stereoselective, and Stereospecific Reactions A stereospecific reaction produces different stereoisomer products from different stereoisomer reactants.

36 Chapter 536 Syn Addition When the two substituents add to the same side Addition of H 2 is a syn addition

37 Chapter 537 Anti Addition When the two substituents add to opposite sides

38 Chapter 538 Stereochemistry of Addition Unmodified only works for addition of X 2 For addition of XY use to calculate X eclipses Y or X opposite to Y in Fischer projection. CIS-SYN-ERYTHRO RULE

39 Chapter 539 Stereochemistry of Addition Cis-Syn-Erythro Example

40 Chapter 540 Stereochemistry of Addition Pro-Fischer Analysis

41 Chapter 541 Stereochemistry of Addition Pro-Fischer Analysis Example


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