Chapter 5 - First Midterm Exam The first CHE 201/203...

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1 First Midterm Exam CHE 201C - Evening class. Last names beginning with A – K report to: Knox 104 Last names beginning with L – Z report to: Knox 110 CHE 203 C All students report to Cooke 121 Students with a conflicting exam in BIO200 should report to HOCHSTETTER 114 at 7:30 pm. The first CHE 201/203 examination: 6:00 – 7:30 pm September 26. There will be a review session during the class on Thursday.
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2 Chirality “Handedness”: right glove doesn’t fit the left hand. Mirror-image object is different from the original object. =>
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3 Stereoisomers Geometric isomers: cis-trans isomers. Enantiomers: nonsuperimposable mirror images, different molecules. => cis -1,2-dichlorocyclopentane trans - 1,2-dichlorocyclopentane H Cl H H H H H H H
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4 Mirror Planes of Symmetry If two groups are the same, carbon is achiral. 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. =>
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5 Mirror Planes of Symmetry C Cl H H H Three mirror planes C H H H H Tetrahedral point group Highly symmetrical C Cl Br H H Single mirror plane C Cl Br F H No mirror planes Chiral
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6 Chiral Carbons Tetrahedral carbons with 4 different attached groups are chiral. Its mirror image will be a different compound (enantiomer). =>
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7 ( 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 H 3 C NH 2 H natural alanine =>
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8 Cahn-Ingold-Prelog Rules Each of the four groups attached to the stereocenter is assigned a priority or preference a, b, c, d. Priority is first assigned on the basis of the atomic number of the atom that is directly attached to the stereocenter. The group with the lowest atomic number is given the lowest priority d; the group with the next higher atomic number is given the next highest priority; and so on . =>
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9 Cahn-Ingold-Prelog Rules When a priority cannot be assigned on the basis of the atomic number of the atoms that are directly attached to the stereocenter, then the next set of atoms in the unassigned groups are examined. This process is continued until a decision can be made. We assign a priority at the first point of difference.
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10 Cahn-Ingold-Prelog Rules Groups containing double of triple bonds are assigned priorities as if both atoms were duplicated or triplicated.
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Chapter 5 - First Midterm Exam The first CHE 201/203...

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