Isomers Flashcards
What is a constitutional isomer?
Structural isomer
Structural isomer
Same chemical formula and different connectivity
Physical property
Characteristics that do not change the composition of a molecule
Chemical Property
Related to the reactivity of the molecule which results from changes in the chemical composition
What usually dictates chemical properties?
Functional groups
What are the two types of stereoisomers?
Conformational and Configurational
Stereoisomers
Same formula and connectivity, different spatial arrangement of atoms
Conformational isomers
Differ in rotation around single bonds
How are configurational isomers interconverted?
Interconverted by breaking bonds
How do you separate a racemic mixture?
Add only one enantiomer of another compound to create two diasteromers (++ and +-) or (– and +-)
Most energetically favorable conformational isomer
Anti
Least energetically favorable conformational isomer
Totally eclipsed
Two types of staggered conformations
Anti and Gauche
Axial position
Perpendicular to plane of ring
Equatorial position
Parallel to plane of ring
What position to bulky groups take in cyclic conformations?
Equatorial
What are the two types of configurational isomers?
Enantiomers and Diastereomers
Enantiomers
Nonsuperimposable mirror images
Nonsuperimposable mirror images
Enantiomers
Are diastereomers mirror images?
No
Chiral
Mirror image cannot be superimposed on original object
Optical activity
Rotation of plane-polarized light by a chiral molecule
Molecule that rotates light clockwise
Dextrorotatory
Dextrorotatory designation
d- or +
d- designation
Rotates light clockwise
+ designation
Rotates light clockwise
Molecule that rotates light counter clockwise
Levorotatory
Levorotatory designation
l- or -
l- designation
rotates light counterclockwise
- designation
rotates light counterclockwise
Racemic mixture
Equal + and -
No optical activity
Does a racemic mixture have optical activity
No
Calculation of specific rotation
Specific rotation = observed rotation/(concentration times length of tube)
Most stable cyclohexane configuration
Chair
Diastereomers
Contain two or more chiral centers and differ at some but not all of these centers
How many stereoisomers does a compound with n chiral centers have?
2^n
What are geometric isomers?
Cis/trans isomers
Meso compound
Has multiple chiral centers but also contains a plane of symmetry and does not rotate light
Is a meso compound optically active?
No
Relative conformation
Configuration in relation to another chiral molecule
Absolute conformation
Exact spatial arrangement of atoms/groups
Z conformation
Two highest priority groups around a double bond are on the same side of the bond
E conformation
Two highest priority groups around a double bond are on opposite sides of the bond
Which direction do wedge bonds project?
Out of the plane of the page
Which direction do dashed bonds project?
Into the plane of the page
In a fischer projection which direction do vertical lines project?
Into the plane of the page
In a fischer projection which direction do horizontal lines project?
Out of the plane of the page
R conformation
Clockwise 1-3 around a chiral center
S conformation
Counterclockwise 1-3 around a chiral center
When you skip #4 to assign R/S, will the designation be the same or opposite?
Opposite
When you make 1 switch to assign R/S, will the designation be the same or opposite?
Opposite
When you move #4 to the back, how do you further manipulate the Fischer projection and will the designation be the same or opposite?
Switch the other two groups and then it will be the same
What are the length units in calculation of specific rotation?
decimeters (10dm in 1m)
What is the concentration unit in calculation of specific rotation?
g/mL
