Organic Chemistry, 5th Edition L G. Wade, jr Chapter 5 Stereochemistry Jo blackburn Richland College, Dallas, TX Dallas county community college district C 2003. Prentice hal
Chapter 5 Stereochemistry Jo Blackburn Richland College, Dallas, TX Dallas County Community College District © 2003, Prentice Hall Organic Chemistry, 5th Edition L. G. Wade, Jr
Chirality Handedness: right glove doesnt fit the left hand Mirror-image object is different from the original object > h
Chapter 5 2 Chirality • “Handedness”: right glove doesn’t fit the left hand. • Mirror-image object is different from the original object. =>
Stereoisomers Geometric isomers: cis-trans isomers Enantiomers: nonsuperimposable mirror images, different molecules > tfiltf H H cis-1, 2-dichlorocyclopentane trans-1, 2-dichlorocyclopentane Chapter 5
Chapter 5 3 Stereoisomers • Geometric isomers: cis-trans isomers. • Enantiomers: nonsuperimposable mirror images, different molecules. => cis-1,2-dichlorocyclopentane trans -1,2-dichlorocyclopentane H Cl H Cl H Cl H Cl H Cl Cl H H Cl Cl H
Chiral carbons Tetrahedral carbons with 4 different attached groups are chiral Its mirror image will be a different compound(enantiomer) > mirror Chapter 5
Chapter 5 4 Chiral Carbons • Tetrahedral carbons with 4 different attached groups are chiral. • Its mirror image will be a different compound (enantiomer). =>
Mirror Planes of Symmetry f If two groups are the same, carbon is achiral (animation KH H · A molecule with an internal mirror CI CI plane cannot be Internal mirror plane chiral of symmetry(σ) Caution! If there is no plane of symmetry, molecule may be chiral or achiral. See if mirror image can be superimposed. = Chapter 5
Chapter 5 5 Mirror Planes of Symmetry • If two groups are the same, carbon is achiral. (animation) • A molecule with an internal mirror plane cannot be chiral.* Caution! If there is no plane of symmetry, molecule may be chiral or achiral. See if mirror image can be superimposed. =>
(尺),(S) Nomenclature Different molecules(enantiomers)must have different names Usually only one enantiomer will be biologically active Configuration around the chiral carbon is specified H3C H with(R) and (s) natural alanine Chapter 5
Chapter 5 6 (R), (S) Nomenclature • Different molecules (enantiomers) must have different names. • Usually only one enantiomer will be biologically active. • Configuration around the chiral carbon is specified with (R) and (S). C C O OH H3C NH2 H natural alanine =>
Cahn-Ingold-Prelog rules e c Assign a priority number to each group attached to the chiral carbon Atom with highest atomic number assigned the highest priority #1 In case of ties look at the next atoms along the chain Double and triple bonds are treated like bonds to duplicate atoms Chapter 5
Chapter 5 7 Cahn-Ingold-Prelog Rules • Assign a priority number to each group attached to the chiral carbon. • Atom with highest atomic number assigned the highest priority #1. • In case of ties, look at the next atoms along the chain. • Double and triple bonds are treated like bonds to duplicate atoms. =>
Assign Priorities O、2OH C H3C H CI natural alanine CH expands to c CH(CH3) O C-CH CHOH CH(CH3)2 H CHoH Chapter 5
Chapter 5 8 Assign Priorities C C O OH H3C NH2 H natural alanine 1 2 3 4 Cl Cl H H * 1 2 3 4 1 2 3 4 => C C O H C H CH2 CH2OH CH(CH3) 2 * C C C CH2OH CH(CH3 ) 2 H O O C C H CH2 C * expands to
Assign(R)or(s) Working in 3d, rotate molecule so that lowest priority group is in back Draw an arrow from highest to lowest priority group Clockwise=(R), Counterclockwise=(s=> rotate C (S)enantiomer Chapter 5
Chapter 5 9 Assign (R) or (S) • Working in 3D, rotate molecule so that lowest priority group is in back. • Draw an arrow from highest to lowest priority group. • Clockwise = (R), Counterclockwise = (S) =>
Properties of Enantiomers Same boiling point, melting point, density Same refractive index Different direction of rotation in polarimeter Different interaction with other chiral molecules Enzymes Taste buds. scent Chapter 5 10
Chapter 5 10 Properties of Enantiomers • Same boiling point, melting point, density • Same refractive index • Different direction of rotation in polarimeter • Different interaction with other chiral molecules – Enzymes – Taste buds, scent =>
