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Chapter 5: Stereochemistry. CH 5-1 Introduction Isomer Review (Constitutional vs Stereoisomers) Chirality Chiral Carbon ( chiral centers ) Enantiomers : mirror-image stereoisomers Drawing Stereoisomers: zig/zag structures Stereochemistry Nomenclature: R,S configurations
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Chapter 5: Stereochemistry CH 5-1 Introduction • Isomer Review (Constitutional vs Stereoisomers) • Chirality • Chiral Carbon (chiral centers) • Enantiomers: mirror-image stereoisomers • Drawing Stereoisomers: zig/zag structures • Stereochemistry Nomenclature: R,S configurations • Diastereomers and Meso compounds: molecules with multiple chiral centers; Fisher Projections. • Stereoisomers in cycloalkanes • Properties of Chiral Molecules
Isomer Update (geometric)
Chirality Chiral objects (and molecules) have no plane of symmetry and can not be superimposed on their mirror images…… Huh?
Chirality “left handed” “right handed”
Chirality Chiral molecules have no plane of symmetry and can not be superimposed on their mirror images “Z” form of DNA “B” form of DNA
Chirality Summary Chiral molecules and objects have no plane of symmetry and can not be superimposed on their mirror images Scissors Pyramid Basketball Coffee mug (no printing) Cylinder Key Cell phone Baseball glove A B C D E F G H I J What about Carbon Atoms?
Chiral Carbon (Chiral Center) • Chiral carbon (chiral center) must be sp3 hybridized (tetrahedral) • Must have 4 different atoms or groups bonded to it (no plane of symmetry) • Stereoisomers: Molecules with the same formula and connectivity, but are not superimposable (different 3-D connectivity). Caraway Spearmint
Chiral Organic Molecules Enantiomers: Mirror-Image Stereoisomers • A chiral molecule must have at least one sp3 chiral carbon. • Enantiomers: A pair of stereoisomers that are non-superimposable mirror images (easier definition coming).
2-D structure: Draw accurate 2-D and 3-D zig-zag line structures for 3-chloro-4-ethyl hexane: ● 3-D structures (chiral center only): ● ● • These two molecules represent a pair of Enantiomers. • These are mirror image Stereoisomers, i.e., two positions to the chiral carbon (Cl & H) have switched. • Enantiomers have identical physical and chemical properties.