OChem2 Isomers Flashcards
Chemical compounds that have the same molecular formula but differ in their atomic connectivity, rotational orientation, or 3D position of their atoms
Isomers
Compounds that share ONLY their molecular formula, their atomic connections may be completely different. They often have very different chemical and physical properties.
Structural Isomers
Isomers with the same chemical formula with the same atomic connectivity. The only difference is how atoms are arranged in space.
Stereoisomers
Compounds that differ in the position of substituents attached to a double bond.
If two substituents are on the same side, the double bond is calleda __ double bond
If they are on opposite sides, it is called a ___ double bond
Geometric isomers
Cis
Trans
If the two highest priority substituents of a polysubstituted double bond are lie on the same side of the double bond, it is called
If the two highest substituents lie on opposite sides, it is called
Z
E
An object that is not superimposable upon its mirror image is called
Objects that can be superimposed are called
Chiral
Achiral
How many different substituents must a carbon have to be considered chiral?
4
Chiral objects that are nonsuperimposable mirror images are a specific type of stereoisomer and are called
enantiomers
The configuration of a chiral molecule relative to another chiral molecule
This describes the spatial arrangement of these atoms or groups
Relative configuration
Absolute configuration
If the priority of a chiral molecule is counterclockwise, it is
If it is clockwise, it is
S
R (clockwise is like turning steering wheel to the right)
Which take higher priority: molecules of higher atomic number or lesser atomic number
Higher atomic numbers take precedence
Enantiomers have identical chemical and physical properties except for one exception, what is it?
Optical activity
A compound that rotates the plane of polarized light to the right, or clockwise, is_____ and is labeled ____
A compound that rotates the plane of polarized light to the left, or counter clockwise, is ___ and is labeled ____
Dextrorotatory (+)
Levorotatory (-)
The amount of rotation of light due to chirality depends upon two things…
What is the specific rotation equation?
Concentration of the chiral molecule
Length of tube through which is passes
specific rotation = observed rotation/(concentration *length)
A mixture of equal concentrations of both the + and - enantiomers of a chiral molecule is called
Is optical activity observed?
Racemic mixture/modification
No.
For any molecule with n chiral centers, how many possible steriosomers are there?
For example, 2 chiral centers = how many possible steriosomers
2^n
4
Sterioisomers that are not mirror images are called
Diasteriomers
A molecule with 2 or more chiral centers that has a line of symmetry within it is called a
Are they optically active?
meso compound
Nope.
Compounds that differ only by rotation about one or more single bonds. Essentially they represent the same compound in a slightly different position
What is use to depict the different configurations?
Conformational isomers
Newman projection
The most stable conformation is when 2 methyl groups on a molecule with two chiral centers are oriented ____ degrees from each other
There is no overlap in the line of sight so the molecule is said to be in ___ conformation
180 degrees
staggered, anti
The other type of staggered conformation, called ____, occurs when the two methyl groups of a molecule with two chiral centers are 60 degrees apart
Gauche
To convert from the anti to the gauche conformation, the molecule must pass through an _____ conformation in which the two methyl groups are 120 gegrees apart and overlap with the H atoms on the adjacent carbon.
When two methyl groups overlap with each other, the molecule is said to be _____ and is in its highest energy state
Eclipsed
Totally eclipsed (think solar eclipse)
In cycloalkanes, this type ostrain results when bond angles deviate from their ideal values
This type occurs when cyclic molecules must assume conformations that have eclipsed interactions
This results when atoms or groups compete for the same space
Angle Strain
Torsional Strain
Nonbonded Strain
What is the most stable conformation of cyclohexane?
Why?
The chair conformation
All 3 types of strain are eliminated
In the chair conformation of cyclohexane, the hydrogen atoms that are perpendicular to the plane of the ring are called
The ones that are parallel are called
Which position is favored?
Axial
Equatorial
The equatorial position because of steric repulsion with other axial substituents
The interconversion between the two chairs can be slowed or even prevented if a sterically _____ group is attached to the ring
Sterically bulky, i.e.t-butyl
Bulky substituents prefer the axial or the equatorial position?
Equatorial
How does a Br2 molecule add to double bonds?
Anti. Not syn.
