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Chapter 5
Stereochemistry

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05-00CO
Title
Pair of Enantiomers
Caption
A molecule that has a nonidentical mirror image, which does not contain a plane of symmetry is said to be chiral.
Notes
The most familiar chiral objects are your hands. A plane of symmetry is a plane that cuts a molecule in two halves, each of which is the mirror image of the other.
Keywords
enantiomers,chiral
05-00-02UN
Title
Isomer Flowchart
Caption
The relationship between different kinds of isomers.
Notes
Constitutional isomers differ in connectivity, and stereoisomers differ in the way their atoms are arranged in space.
Keywords
stereoisomer, isomer, flowchart, constitutional, connectivity
05-00-06
Title
Cis-trans Isomers
Caption
Ball-and-stick and Kekulé structures of cis- and trans-2-pentene.
Notes
Configurational isomers cannot interconvert because the double bond cannot rotate. Cyclic compounds can also have cis and trans isomers because the cyclic system prevents free rotation about the single bonds.
Keywords
configurational, isomers, 2-pentene, ball-and-stick, Kekulé
05-01
Title
Figure 5.1
Caption
Original and mirror images of a hand and a chair.
Notes
A chiral object is not the same as its mirror image—they are nonsuperimposable (i.e., the hand). An achiral object is the same as its mirror image—they are superimposable (i.e., the chair).
Keywords
mirror, image, hand, chair, chiral, achiral, superimposable, nonsuperimposable, figure, 5.1
05-01-01UN
Title
Molecule with Asymmetric Carbon
Caption
A molecule with an asymmetric carbon is chiral.
Notes
Carbon atoms which have four different things attached to them are asymmetric, or chiral. They are not superimposable with their mirror images.
Keywords
molecule, asymmetric, carbon, chiral, superimposable
05-01-10UN
Title
Chiral and Achiral Molecules
Caption
Structures of a chiral molecule, an achiral molecule, and mirror images of the two.
Notes
A chiral molecule has a nonsuperimposable mirror image. An achiral molecule has a superimposable mirror image.
Keywords
chiral, achiral, molecules, nonsuperimposable, mirror, image, superimposable
05-01-14UN
Title
Stereocenters
Caption
Five stereocenters depicted in three molecules.
Notes
A stereocenter is an atom at which the interchange of two groups yields two different nonsuperimposable molecules. Asymmetric carbons are stereocenters and so are carbons which hold attached substituents in E or Z isomeric configurations.
Keywords
stereocenters, interchange, asymmetric, nonsuperimposable
05-01-16UN
Title
A Chiral Molecule
Caption
A chiral molecule composed of an asymmetric carbon and four different kinds of attached atoms.
Notes
To assign an R or S configuration to a stereocenter of a chiral molecule, the Cahn-Ingold-Prelog system is used to assign relative priorities to all of the groups attached to the stereocenter.
Keywords
chiral, molecule, asymmetric, R, S, configuration, stereocenter, Cahn-Ingold-Prelog, priorities
05-01-17UN
Title
Determining Configuration Step 1
Caption
The first step in determining the configuration of a stereocenter is to number attached groups in descending order of priority using the Cahn-Ingold-Prelog rules.
Notes
The only carbons that can be chiral stereocenters are sp3-hydridized carbons. Chiral centers must have four groups bonded to them. The three groups attached to an sp2-hybridized carbon all lie in a plane, and if a mirror is oriented parallel to this plane, original and mirror images will be identical (superimposable).
Keywords
chirality, centers, determining, configuration, step, 1, chiral, stereocenter, Cahn-Ingold-Prelog
05-01-18UN
Title
Determining Configuration Step 2
Caption
The second step in determining the configuration of a chiral stereocenter is to orient the lowest-priority group behind the stereocenter and determine whether the remaining groups are priority-ordered in a clockwise or counterclockwise fashion around the stereocenter.
Notes
If groups are ordered around a chiral stereocenter such that the lowest-priority group is behind the stereocenter and the remaining groups are in front of the stereocenter and ordered clockwise around the stereocenter in ascending priority-numbered order (i.e., 1 to 3 for carbon), the chiral stereocenter is assigned an "R" designation. The "R" in R configuration is from rectus, which is latin for "right." Counterclockwise ordering yields an "S" (sinister, or left) designation.
Keywords
R, configration, determining, configuration, step, 2, priority, clockwise, counterclockwise, rectus, sinister, S
05-01-19UN
Title
Steering-Wheel Analogy to Priority Assignment
Caption
Turning a steering wheel clockwise results in a right (rectus, R) turn and turning it counterclockwise results in a left (sinister, S) turn.
Notes
The steering-wheel analogy aids in remembering that ordering highest priority groups in front of a chiral stereocenter in a clockwise fashion results in an R configuration, whereas orienting these groups in a counterclockwise fashion yields an S onfiguration.
Keywords
steering-wheel, analogy, priority, assignment, clockwise, counterclockwise, R, S
05-01-41UN
Title
Plane-Polarized Light
Caption
Plane-polarized light oscillates only in a single plane.
Notes
Plane-polarized light is produced by passing normal light through a polarizer such as a polarized lens or Nicol prism.
Keywords
plane-polarized, light, polarized
05-01-44UN
Title
Achiral Compound in Plane-Polarized Light
Caption
An achiral compound does not rotate the plane of polarized light. It is optically inactive.
Notes
When plane-polarized light passes through a solution of achiral molecules, the light emerges from the solution with its direction of polarization unchanged, because there is no asymmetry in the molecules.
Keywords
propagation, rotate, light, achiral, plane-polarized
05-01-45UN
Title
Chiral Compound in Plane-Polarized Light
Caption
A chiral compound rotates the plane of polarized light in either a clockwise or counterclockwise direction.
Notes
If one enantiomer rotates the plane of polarized light in a clockwise direction, its mirror image will rotate the plane of polarized light by an equal amount but in the opposite direction.
Keywords
propagation, rotate, light, chiral, plane-polarized
05-02
Title
Schematic of a Polarimeter
Caption
The amount that an optically active compound rotates the plane of polarized light can be measured by a polarimeter.
Notes
Because the amount of rotation depends on the wavelength of the light used, the light source for a polarimeter must produce light with a single wavelength.
Keywords
polarimeter, schematic, rotation, optically active
05-02-05UN
Title
Enantiomeric Excess Formula
Caption
Calculation of enantiomeric excess for a compound with an optical purity of 40%.
Notes
Optical purity and isomeric purity are not the same. A 50/50 mixture of two enantiomers has a 50% isomeric purity, but a zero optical purity or enantiomeric excess. To convert from enantiomeric excess to isomeric purity, divide the percent enantiomeric excess by two and add the result to 50%.
Keywords
enantiomeric, excess, formula, optical, isomeric, purity
05-02-07UN-A
Title
Erythro and Threo Diastereomers
Caption
Erythro enantiomers are diastereomers of threo enantiomers.
Notes
Diastereomers are stereoisomers which are not mirror images of one another. Erythro enantiomers are stereoisomers with two adjacent chirality centers, which have two similar groups on the same side of the carbon chain, and threo enantiomers have the two similar groups on opposite sides of the carbon chain.
Keywords
stereoisomers, diastereomers, erythro, threo, enantiomers
05-02-07UN-B
Title
Ball-and-Stick Models of 3-Chloro-2-butanol
Caption
Ball-and-stick models of the four isomers of 3-chloro-2-butanol.
Notes
3-Chloro-2-butanol has two erythro enantiomers and two threo enantiomers. Each of the two erythro isomers is a diastereomer of each of the two threo isomers.
Keywords
ball-and-stick, 3-chloro-2-butanol, isomers, erythro, threo, enantiomers, diastereomers
05-02-07UN-C
Title
Isomers of 3-Bromo-2-butanol
Caption
Eclipsed conformations of 3-bromo-2-butanol make it easy to see which isomers are threo and which are erythro.
Notes
3-Bromo-2-butanol has two erythro enantiomers and two threo enantiomers. Each of the two erythro isomers is a diastereomer of each of the two threo isomers.
Keywords
3-bromo-2-butanol, isomers, erythro, threo, enantiomers, diastereomers
05-02-11UN
Title
Cis- and Trans-1-bromo-3-methylcyclobutane
Caption
cis- and trans-1-Bromo-3-methylcyclobutane do not have enantiomers because they have a plane of symmetry.
Notes
These compounds do not contain any chiral centers. The cis isomer and the trans isomer are the only stereoisomers of this compound.
Keywords
1-bromo-3-methylcyclobutane, enantiomers, plane, symmetry, cis, trans
05-02-24UN
Title
Cyclic Meso Compounds
Caption
In the case of cyclic compounds, the cis isomer will be the meso compound.
Notes
The trans isomer for cyclic compounds will be a pair of enantiomers.
Keywords
cyclic, meso, compounds, cis, isomer, trans
05-02-46UN
Title
3-Bromo-2-butanol Isomers
Caption
Named perspective formulas and Fischer projections of the isomers of 3-bromo-2-butanol.
Notes
The first two structures on the left are enantiomers of each other. The last two structures on the right are also enantiomers. Each of the structures in the left pair is a diastereomer of each of the structures in the right pair.
Keywords
3-bromo-2-butanol, isomers, named, perspective, Fischer
05-03
Title
Receptor Binding Sites
Caption
Schematic diagram showing why only one enantiomer is bound by a receptor.
Notes
One enantiomer fits into the binding site and the other does not.
Keywords
receptor, binding, site, schematic enantiomer
05-03-002UN
Title
Thalidomide
Caption
Structural formula and ball-and-stick model of thalidomide showing chiral carbon.
Notes
The l isomer of thalidomide is a severe teratogen, whereas the d isomer is only a mild teratogen.
Keywords
thalidomide, teratogen, d, l, isomer
05-03-014UN
Title
Amine Inversion
Caption
Depiction of amine lone pair flipping from right to left side of an amine molecule during an amine inversion.
Notes
Amine inversion occurs when the lone pair of electrons in the yellow p orbital jumps to the opposite side of the nitrogen atom, reversing the relative sizes of the two lobes of this orbital and flipping the substituents bonded to the nitrogen atom to the opposite side of the nitrogen atom.
Keywords
amine, inversion, lone, pair, flipping
05-03-021UN
Title
Mechanism of Addition of HBr to 1-Butene and 2-Butene
Caption
Carbocation intermediates are flat and planar allowing for the nucleophile to attack the top or bottom, yielding both enantiomers of 2-bromobutane as products.
Notes
A mixture of equal amounts of a pair of enantiomers is called a racemic mixture, a racemic modification, or a racemate.
Keywords
racemic, mixture, enantiomers, mechanism, addition, 1-butene, 2-butene, 2-bromobutane
05-03-031UN
Title
Stereoisomer w/Br Ion
Caption
The carbocation intermediate is flat and planar which allows for the Br ion to attack the top or bottom.
Notes
The product is a racemic mixture, containing both R and S enantiomers.
Keywords
carbocation,Br,racemic
05-03-051UN
Title
Bromonium Ion Potential Map
Caption
Electrostatic potential map of the bromonium ion intermediate in the reaction of cis-2-butene with bromine.
Notes
The bromine blocks one side of the intermediate from attack by bromide ion, forcing the second bromine to add anti to the first bromine.
Keywords
bromonium, potential, map, cis-2-butene, anti
05-03-109P75
Title
End-of-Chapter Problem 75
Caption
Enantiomers of 1,2-dimethylaziridine.
Notes
Enantiomers of 1,2-dimethylaziridine do not undergo amine inversion because the three-membered ring cannot easily achieve the 120-degree angle around nitrogen necessary for it to form the flat transition state required for inversion.
Keywords
end-of-chapter, problem, 75

Title
Table 5.1 Physical Properties of the Stereoisomers of Tartaric Acid
Caption
Notes
Keywords

Title
Table 5.2 Stereochemistry of Alkene Addition Reactions
Caption
Notes
Keywords

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