lecture 3 - Isomers Isomers: different compounds with the...

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1 Stereoisomerism and Chirality Chapter 3 Chapter 3 Isomers Isomers ± Isomers: different compounds with the same molecular formula ± Constitutional isomers: isomers with a different connectivity ± Stereoisomers : isomers with the same connectivity but a different orientation of their atoms in space Chirality ± Chiral Chiral : from the Greek, cheir , hand an object that is not superposable on its mirror image Chirality Chirality ± Achiral : an object that lacks chirality; one that lacks handedness an achiral object has at least one element of symmetry plane of symmetry: an imaginary plane passing through an object dividing it so that one half is the mirror image of the other half center of symmetry: center of symmetry: a point so situated that identical components are located on opposite sides and equidistant from that point along the axis passing through it Elements of Symmetry ± Symmetry in objects Symmetry in objects Elements of Symmetry Elements of Symmetry ± Symmetry in objects Symmetry in objects
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2 Elements of Symmetry Elements of Symmetry ± Symmetry in objects Symmetry in objects This molecule has neither a plane nor a center of symmetry Elements of Symmetry Elements of Symmetry ± Plane of symmetry (cont’d) HO OH mirror plane Chiral Center ± The most common (but not the only) cause of chirality in organic molecules is a tetrahedral atom, most commonly carbon, bonded to four different groups Chiral Center Chiral Center ± A carbon with four different groups bonded to it is called a chiral center all chiral centers are stereocenters, but not all stereocenters are chiral centers ± Enantiomers : stereoisomers that are nonsuperposable mirror images refers to the relationship between pairs of objects
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3 Each molecule has a chiral center. Draw stereorepresentations for the enantiomers of each. p. 115 Enantiomers Enantiomers ± 2-Butanol has one chiral center here are four different representations for one enantiomer OH C H 3 C CH 2 3 H C H 3 C 2 3 H H (1) (2) (3) (4) Enantiomers ± 2-Butanol using (4) as a model, here are two different representations for the enantiomer of (4) (4) OH (4) OH OH representations for the enantiomer of (4) Enantiomers Enantiomers ± The enantiomers of lactic acid drawn in two different representations C C HO 3 H O HO C C 3 H OO H OH OH O OH HO O
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4 Enantiomers Enantiomers ± 2-Chlorobutane CH 3 CHCH 2 3 Cl H Cl H Enantiomers Enantiomers ± 3-Chlorocyclohexene Enantiomers ± A nitrogen chiral center N 2 CH 3 H 3 C N CH 3 3 CH 2 A pair of enantiomers + + R,S Convention for Naming Convention for Naming Chiral Centers
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lecture 3 - Isomers Isomers: different compounds with the...

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