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29 Cards in this Set
- Front
- Back
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Isomer |
Compound with same molecular formula |
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Stereocenter |
Any atom that would become a different stereoisomer if any two groups traded places |
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Constitutional/Structural Isomers |
Molecules with same formula but different bond connectivity |
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Stereoisomers |
Molecules between which the only difference is 3D orientation (their stereochemistry) |
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Cis/trans isomer |
Type of stereoisomer (specifically, a type of diastereoisomer) -Can be an alkene in which there are two different groups on one side of a double bond and two different groups on the other side or can be a cycloalkane (An alkene with the same two groups on one side of a double bond cannot have cis/trans isomerism) |
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Cis isomer |
Alkene or cycloalkane in which the two higher priority groups are both pointed downward or upward from the double bond |
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Trans isomer |
Alkene or cycloalkane in which one of the higher priority groups is pointed downward from the double bond and the other is pointed upward |
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Isomers with chirality centers |
Type of stereoisomer |
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Chiral compounds |
Compounds that have non-superimposable (non-identical) mirror images |
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Enantiomers |
The two non-superimposable (non-identical) mirror images of a chiral compound -Both chiral centers must be inverted in enantiomers -Have same physical properties (e.g. same b.p., m.p., and polarity) except for light rotation (rotate plane-polarized light to the same degree but in opposite directions) -Can be separated in a chiral environment (e.g. by enzymes and smell receptors) |
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Achiral compounds |
Compounds with mirror images that are superimposable (identical) -One or more internal mirror planes in any conformation makes a molecule achiral |
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Optical activity |
Rotation of plane-polarized light |
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Racemic mixture |
A 50/50 mixture of enantiomers -optically inactive |
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D and S designations |
The enantiomer that rotates light to the right is designated 'D' or + and the enantiomer that rotates light to the left is designated 'S' or - -Completely independent of R and S designations |
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Chirality/asymmetric center |
Tetrahedral (sp3-hybridized) atom with 4 different substituents -Is usually carbon but does not have to be -A lone pair counts as a substituent -Any molecule connected to a pi bond cannot be a chirality center because a pi bond counts as two identical substituents |
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R and S designations |
1. Rank the substituents from 1-3 giving the substituent with the highest atomic number the #1 designation, the second highest the #2 designation, and the lowest the #3 designation -if there is a tie, compare the atoms connected to the two tied substituents and rank their substituents, first comparing the two most highly-ranked substituents and then the next two-highest, etc. The first difference between two atoms is the tie-breaker. 2. Draw a circle from the highest to the second-highest to the lowest-ranked substituent -If the turn is clockwise, the chiral center is designated "R" -if the turn is counterclockwise, the chiral center is designated "S" 3. If the 4th-ranked substituent is not facing the back (dashed line), reverse the designation |
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R and S nomenclature |
E.g. (R) 2-bromobutane is a molecule with 1 chirality center (2R, 4R)-2-bromobutane is a molecule with 2 chirality centers |
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Maximum number of stereoisomers |
2n with n = the number of stereocenters |
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E-Z designations |
Applies to cis/trans isomers -Cis isomers are designated "Z" because the two highest-priority substituents are on "ze" same side -Trans isomers (isomers with the two higher priority groups trans to one another) are designated "E" |
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Diastereomers |
Stereoisomers with different physical properties that can be separated using traditional means Must have cis/trans orientation or multiple chirality centers in which some have been inverted but not all |
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Meso compound |
Achiral molecules with chiral centers 1. Must have a chiral center AND 2. Must have an internal mirror plane of symmetry *A meso compound with two chiral centers will have one "R" center and one "S" center -Optically inactive because the two chiral centers rotate light in opposite directions and cancel each other out |
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Fischer Projections |
Projection of a molecule in which a chiral center is represented as the center of a cross, dashed bonds are represented as vertical bond lines, and wedged bonds are represented as horizontal bond lines *Any group extending horizontally from a chiral center is connected to the chirality center by a wedge bond (it faces outward from the center) -Often used to represent carbohydrate molecules |
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Drawing enantiomers |
Have exactly 2 groups attached to each chiral center change places |
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Determining the stereochemical relationship between two molecules |
1. Locate any chirality centers -no chirality centers means it's an achiral molecule 2. Locate any internal mirror planes -any internal mirror planes indicate a meso compound 3. Assign R and S designations to the chirality centers -if there is 1 R and 1 S chirality center in a single molecule, it's a meso compound -if not all R and S designations are inverted, the molecules are diastereomers -if all R and S designations are inverted, the molecules are enantiomers |
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Amine inversion |
If any of an amine chiral center's substituents are larger than a hydrogen and one of the substituents is a lone pair, the molecule is achiral because its mirror images interconvert back and forth constantly and interchangeably -If all 4 of an amine chiral center's substituents are different and there is no lone pair, the molecule is chiral |
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Chiral molecules without a chiral center |
Allenes and biphenyl systems -no chiral center because there is no tetrahedral atom |
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Allenes |
Three carbons connected via double bonds arranged linearly *To be chiral, the carbons on both ends of the molecule must have two different groups attached |
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Biphenyl systems |
To be chiral, at least 3 of the 4 molecules in the ortho positions must be larger than hydrogen -Because of the bulk of the substituents, one of the rings will rotate around the horizontal bond connecting the two rings and remain there (double bonds within the ring systems cannot rotate!) -Achiral if either of the rings have two of the same groups in its ortho positions -Pi bonds don't affect symmetry in rings because the electrons are delocalized through resonance |
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Treatment of an alkene with a different molecule |
The atoms in the molecule are added to opposite sides of the double bond in the alkene in the trans positions |
