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Lecture Organic chemistry - Chapter 5: Image and mirror image. This chapter includes contents: Image and mirror image of limonene, a new type of stereoisomerism, enantiomers, stereocenters, asymmetric carbon: No mirror plane, symmetry in nature, the polarimeter,.and other contents. | Chapter 5: Image And Mirror Image Image And Mirror Image Of Limonene Spruce tree Orange “Handedness” A New Type Of Stereoisomerism Recall: a. Constitutional isomers (butane, 2-methylpropane) b. Stereoisomers (cis-trans cycloalkanes) c. Image-mirror image stereoisomers Remember the bromination of butane: Now: We thought these were identical 50:50 chance 50:50 mixture The two 2-bromobutanes are not identical, because they are not superimposable: They are image and mirror image. 50:50 Mixture of enantiomers: Racemic mixture or racemate The two isomers are labelled enantiomers. Molecules that lack reflection symmetry are called chiral (from Greek: cheir, hand “handedness”). Enantiomers 8/11/2015 © Univesity of California 4 enantios, Greek, opposite If image and mirror image of a molecule are superimposable it is achiral. Quick test: presence of a mirror plane. Chiral molecules lack a mirror plane. Most organic molecules owe their chirality to the presence of a stereocenter, usually | Chapter 5: Image And Mirror Image Image And Mirror Image Of Limonene Spruce tree Orange “Handedness” A New Type Of Stereoisomerism Recall: a. Constitutional isomers (butane, 2-methylpropane) b. Stereoisomers (cis-trans cycloalkanes) c. Image-mirror image stereoisomers Remember the bromination of butane: Now: We thought these were identical 50:50 chance 50:50 mixture The two 2-bromobutanes are not identical, because they are not superimposable: They are image and mirror image. 50:50 Mixture of enantiomers: Racemic mixture or racemate The two isomers are labelled enantiomers. Molecules that lack reflection symmetry are called chiral (from Greek: cheir, hand “handedness”). Enantiomers 8/11/2015 © Univesity of California 4 enantios, Greek, opposite If image and mirror image of a molecule are superimposable it is achiral. Quick test: presence of a mirror plane. Chiral molecules lack a mirror plane. Most organic molecules owe their chirality to the presence of a stereocenter, usually a carbon with 4 different substituents: an asymmetric carbon. Stereocenters C Stereocenter * labelled Asymmetric Carbon: No Mirror Plane Symmetry In Nature 20,000 : 1 Escargot Symmetry is beautiful, or is it ? Symmetry in Art: M. C. Escher Waterfall Drawing Hands Möbius Strip 8/11/2015 © Univesity of California 13 August Ferdinand Möbius Born: 17 Nov 1790 in Schulpforta, Saxony (now Germany) Died: 26 Sept 1868 in Leipzig, Germany Auguste Rodin: La Cathedral The Various Kinds Of Isomers THeads Walba 8/11/2015 © Univesity of California 15 Movie 5:04 min-Takemetotheriver “Handedness” (i.e., left or right) is called the absolute configuration. Measured by: X-ray crystal structure = “Photo.” Enantiomers: How To Tell Which Is Which The Polarimeter One enantiomer (image) rotates light dextrorotatory (clockwise), (+)-enantiomer The other enantiomer (mirror image) rotates light levorotatory (counter-clockwise), (-)-enantiomer. 2. .
