OCHEM_UNIT_7 - OCHEM UNIT 7: STEREOCHEMISTRY: CHIRALITY A....

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Unformatted text preview: OCHEM UNIT 7: STEREOCHEMISTRY: CHIRALITY A. ISOMERISM REVISITED 1. INTRODUCTION There are two major types of isomers:-constitutional isomers-stereoisomers 2. STRUCTURAL OR CONSTITUTIONAL ISOMERS REVISITED Structural isomers are compounds that have the same molecular formula , but have different atom connectivities. They are not interconvertible by a simple C C rotation. Ex: C 5 H 12 CH 3 CH 3 (CH 2 ) 3 CH 3 and CH 3 CHCH 2 CH 3 3. STEREOISOMERS OR STEREOMERS Stereoisomers are isomers that have the same molecular formula, the same atom connectivities, but different spatial arrangements of their atoms. There are 2 types of configurations for stereoisomers:-enantiomers = mirror images-diastereomers = not mirror images 1 Ex: cis- 1,3- dimethylcyclopentane and trans- 1,3- dimethylcyclopentane are diastereomers. CH 3 CH 3 CH 3 CH 3 Read pages 163-164 . Do Problem 5.2. B. HANDEDNESS AND CHIRALITY 1. HANDEDNESS-handedness = similarity to hands-left hand and right hand = not superimposable = mirror images A chiral object is an object that is not superimposable to its mirror image. Ex: left hand and right hand. A chiral molecule is a molecule that is not superimposable to its mirror image. Ex: CBrClFI 2 Enantiomers are mirror images that are not superimposable to each other. 2. PLANE OF SYMMETRY A plane of symmetry is a plane that cuts an object into equal halves. Note: any object or molecule that possesses a plane of symmetry is superimposable to its mirror and is said to be achiral. No enantiomers for an achiral molecule. Read pages 164 - 165. Do problems 5.3, 5.4 and 5.5 page 166 - 167. C. PREDICTION OF CHIRALITY 1. STEREOGENIC CENTER OR CHIRAL CENTER (ASYMMETRIC CARBON) A carbon that has 4 different groups attached to it is chiral and is called a (tetrahedral) stereogenic center . 3 Note: A molecule that has one stereogenic center is always chiral. 2. DISCOVERY OF CHIRALITY-discovered by French Jean Baptist Biot in 1815.-work extended by Louis Pasteur (1822-1895) . Note: enantiomers have same connectivities, same MP and BP, same solubility in chiral solvents, same density, but are mirror images. They are also affected differently by plane-polarized light. 3. PREDICTION OF CHIRALITY a. Write down the structural formula b. Identify the stereogenic center....
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This note was uploaded on 04/19/2011 for the course CHEMISTRY 2423 taught by Professor Kay during the Spring '08 term at Dallas Colleges.

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OCHEM_UNIT_7 - OCHEM UNIT 7: STEREOCHEMISTRY: CHIRALITY A....

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