Stereochemistry Flashcards
The objective of this deck is to learn the basic principles and vocabulary of the stereochemistry study in organich chemistry.
What is a stereoisomer?
An isomer that has the same constitution but differ in the spatial arrangement of their atoms.
Who (Lord Kelvin), and in what year coined a word that describes nonsuperimposable objects?
William Thomson in 1894 coined the word chiral.
What’s a chiral molecule?
A molecule whose two mirror-image forms are not superimposable in three dimensions.
What is the Greek word for chiral, and what does it mean?
cheir, means “hand”
What is the opposite of chiral?
Achiral- a molecule that is superimposable on its mirror image.
Name the following compound and decide whether it is chiral or achiral:
BrClFCH
bromochlorofluoromethane is chiral
What types of molecules tend two be chiral? (e.g what types of groups should they have)
Molecules in which there is a carbon that is attached to four different groups.
What is an enantiomer?
They are stereoisomers that are related as an object and its nonsuperimposable mirror image.
How many enantiomers can a chiral molecule have?
One.
In C(w,x,y,z), how many groups have to change in order for the molecule to be converted to its enantiomer, and what happens if three groups change.
Two groups have to change because if three groups change the molecule will still be the same but in a different orientation.
Is chlorodifluoromethane chiral or achiral?
Achiral.
What other terms describe a chirality center?
- asymmetric chenter
- asymmetric carbon
- chiral center
- stereogenic center
- stereocenter
Is 2-butanol chiral or achiral?
Chiral.
Is 2-propanol chiral or achiral?
Achiral.
Can a carbon involved in a double or triple bond be a chirality center?
No.
How can a carbon atom in a ring be a chirality center?
If it has two different groups and the two paths traced around the ring are different.
A molecule with a plane of symmetry is superimposable/nonsuperimposable and it is chiral/achiral.
Superimposable, achiral.
What are the requirements for a center of symmetry?
A line drawn from a point in the center of a molecule to some element, when extended in an opposite direction will ecncounter the same element again.
Who is (Jacobus and Joseph Achille) and in what year did they propose what?
Van’t Hoff and Le Bel in 1874 they proposed that four bonds of carbon were directed toward the corners of a tetrahedral.
What did van’t Hoff and Le Bel’s proposal mean for molecules?
That molecules with the same constitution could differ in the arrangement of their atoms in space. (stereoisomers are possible)
What is optical activity?
The ability of a chiral substance to rotate the plane of
plane-polarized light.
What are two properties of the light that measures optical activity?
- It has a single wavelength
- It is plane polarized
Chiral/achiral substances can rotate the plane of plane-polarized light.
Chiral molecules.
What wavelength is used in the light that measures optical activity?
589 nm
(It corresponds to a yellow light produced by a sodium lamp)
What french physicist and in what year did he/she discover the phenomenon of optical activity?
Jean-Baptiste Biot in 1815.
What is an ideal phase of a substance to be used as a sample in a polarimeter? In the solution form, what are the best solvents that can be used?
The liquid phase should be used.
The best solvents are:
- water
- chloroform
- ethanol
What does the analyzer in a polarimeter do?
It measures the magnitude and direction of the observed rotation.
To be optically active, the sample must contain a —–substance and one—–must be present in ——-of the other.
Chiral, enantiomer, excess.
Optically inactive substances do/do not change the plane of polarized light. All chiral/achiral substances are optically inactive.
Do not/achiral.
What is a racemic mixture?
A mixture that contains equal quantities of enantiiomers. They are optically inactive.
Describe an optically pure mixture.
All of the molecules are the same handedness. Only one enantiomer is present in the substance.
What’s the equation for optical purity? (a.k.a percent enantiomeric excess)
OP=% excess
OP=% enantiomer-% enantiomer
What is + and - rotation?
Positive rotation is rotation of the plane of polarized light clockwise and negative rotation is counterclockwise.
Give the definition and formula for specific rotation.
Specific rotation accounts for the effects of path length and concentration in different filled polarimeters.
[a]=100a/cl
How many cm is one decimeter (dm)?
10 cm.
What is absolute configuration?
The exact spatial arrangement of groups in a chirality center in a three dimensional molecule.
Compounds with different/same relative configurations have optical rotations of same/opposite signs.
Same,opposite.
True or False
In a reaction that does not involve any of the bonds to the chirality center, the starting compound and the product have the same relative configuration.
True.
Who (R.S, Sir Christopher, Vladimir) developed a system (what system) to deal with the problem of (what) at a chirality center.
Cahn, Ingold, Prelog.
Sequence rules system.
Absolute configuration.
Describe the sequence rules deviced by Cahn, Ingold and Prelog.
- Identify a chirality center (carbon).
- Point atom with lowest atomic number away from you.
- Find atom with highest atomic number.
- Check from highest to lowest atomic number.
Define R and S.
R is clockwise and S is counterclockwise.
What is the standard method for stereochemical notation?
The Cahn-Ingold-Prelog system.
What German chemist abbreviated stereochemical information?
Emil Fischer.
What are Fischer projections?
Molecular drawings in which the vertical bonds are always directed away from you and the horizontal bonds are directed toward you.
In Fischer projections the lowest/highest numbered carbon is at the top/bottom.
Lowest/top.
How do you verify that a Fischer projection has the R configuration?
Ensure that the lowest-ranked atom is pointing away from you and rank the remaining atoms in the order of decreasing precedence. If the path traced is clockwise then it is in R configuration.
Enantiomers have different characteristics for properties that depend on—-but not for the usual physical properties such as —-,——, and —–.
The arrangement of atoms in space. Density, melting point, and boiling point.
Read “When Drug Molecules Look In The Mirror.”
Yes.
