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27 Cards in this Set
- Front
- Back
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What is stereochemistry?
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Study of 3D molecules.
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What is chiral?
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Non-superimposable mirror images.
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What is achiral?
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Superimposable mirror images.
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What two situations will lead to a molecule being achiral?
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If the molecule has a plane of symmetry or a center of symmetry.
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What is an isomer?
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Different compounds with the same molecular formula.
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What are stereoisomers?
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The same molecular formula and connectivity but different arrangement in space (cis, trans).
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What are configurational isomers?
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Isomers that differ by the configuration of substituents on an atom (cis, trans).
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What are enantiomers?
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A pair of non-superimposable mirror images.
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What is a chiral center?
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Typically a carbon atom with four different substituents.
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What are diasteromers?
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Stereoisomers that are not mirror images.
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What are conformational isomers?
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Are stereoisomers that do not require bond breaking (Gauche, anti).
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What is the order of priority for the R,S system?
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1. Each atom bonded to chiral center assigned priority according to atomic number.
2. If atoms tie, look to next set of atoms 3. Atoms bonded with double or triple bond are counted two or three times |
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How many stereoisomers exist in a molecule with more than one chiral center?
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2^n
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What is a meso compound?
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An achiral compound possessing two or more chiral centers that also has chiral isomers.
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What are characteristics of meso compounds?
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Because of two+ chiral centers, number of isomers less than number predicted by 2^n rule. This happens because two of the pairs are superimposable mirror images, thus the same molecule.This means that there is a plane of symmetry in two of the structures. As with tartaric acid the the meso compound is a diastereomer of each member of the pair of enantiomers.
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Do enantiomers have the same chemical and physical properties?
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Yes unless exposed to a chiral environment such as a chiral molecule or plane polarized light.
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What do the vertical lines, horizontal lines mean in a Fischer projection?
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Vertical are into page, horizontal are out of page for a chiral center.
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Is trans-1,2-cyclopentadiol chiral?
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No, achiral and also a meso compound.
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What is relevant about a 1,4 disubstituted cyclohexane?
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It is achiral. Each should-be chiral carbon sees the same thing as it goes around the ring in either direction.
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What are the Latin terms for rotating light right, left?
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Right is dextrorotary, left is levorotary.
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What is observed rotation and how does it relate to specific rotation?
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Observed rotation is the degree to which light is rotated when passed through a compound. Specific rotation then standardizes this observed rotation by taking into account the path length and concentration of the compound.
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What is a racemic mixture?
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An equimolar mixture of two enantiomers which is therefore optically inactive.
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What is optical purity?
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A way of determining how much of of one enantiomer is present in a mixture. This is found by dividing the specific rotation of the mixture by the specific rotation of the enantiomerically pure sample.
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What is enantiomeric excess?
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The difference between the percentages of two enantiomers in a mixture.
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Why is chirality important for enzymes?
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Chirality allows an enzyme to distinguish between different enantiomers.
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What is resolution?
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The separation of enantiomers by forming one into diastereomers (with different physical and chemical properties), using these differences to extract, and then converting back to enantiomers.
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What lab examples have been presented as means of resolution?
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TLC, chromatography.
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