Isomers Flashcards
Isomers are molecules with the
Same molecular formula but difference in structure
Stereoisomers differ in how
Atoms are oriented
Horizontal wedges in Fischer projections display atoms going
Out of the plane / page
Vertical wedges in Fischer projections display atoms going
In the plane / page
The amount of rotation by polar polarized light depends on the
Number of molecules a light wave encounters
The number of possible stereoisomers is given by equation
2^n
The equation for specific rotation is
Observed retention / Concentration • Length
Epimers are
Diastereomers that differ by 1 C
Conformational isomers differ by
Rotation
Conformational isomers differ in
Rotation around sigma bonds
Configurational isomers can be interconverted by
Breaking bonds
Ring strain can be caused by:
- Angle strain
- Torsional strain
- Steric strain
Angle strain results when
Bond angles deviate from their ideal values by being
stretched or compressed.
Torsional strain results when cyclic molecules must
Assume conformations that have eclipsed or gauche interactions
Chair confirmation is one such type that
Eliminates all three strains that cause overall ring strain
The two categories of configurational isomers are
- Enantiomers
- Diastereomers
Achiral objects have
Mirror images that can be superimposed
Two molecules that are nonsuperimposable mirror images of each other are called
Enantiomers
Enantiomers have identical physical and chemical properties with two notable exceptions:
- Optical activity
- Reactions in chiral environments
Enantiomers have nearly identical physical properties and chemical properties, but they
Rotate plane-polarized light in opposite directions
Diastereomers are
Non-mirror-image configurational isomers
Diastereomers are required to have
Multiple chiral centerd
Possible stereocenters can be determined by the equation
2^n
Cis–trans isomers are a type of
Diastereomers
For a molecule to have optical activity, it must have
- Chiral centers
- Lack a plane of symmetry
A molecule with chiral centers that has an internal plane of symmetry is called a
Meso compound
The configuration of a stereoisomer refers to the
Spatial arrangement of the atoms or groups in the molecule.
The relative configuration of a chiral molecule is its configuration in relation to
Another chiral molecule
The absolute conformation of a chiral molecule describes the
Exact spatial arrangement of these atoms or groups, independent of other molecules
Two atomic orbitals may combine to form:
- Bonding molecular orbital
- Antibonding molecular orbital
- Hybridized orbitals
Molecular orbitals can contain a maximum of
Two orbitals
A π bond is weaker than a single bond because there is
Less overlap between the unhybridized p-orbitals of a π bond than between the s-orbitals or hybrid orbitals of a σ bond.
Why is a single bond stronger than a π bond?
S-orbitals have more overlap than p-orbitals.
A resonance structure describes
A potential arrangement of electrons in a molecule
Compared to single bonds, triple bonds are
More rigid
