Chapter 4 Test Flashcards
What does chiral mean?
Molecules that are not superimposable on their mirror images, so they can exist as two enantiomers
What does achiral mean?
Molecules that are identical to their mirror image. They have a plane of symmetry in one or more of their conformations
What does enantiomers mean?
Stereoisomers that are non-superimposable mirror images; relationship between pairs of molecules
What does meso compounds mean?
Molecules that contain a stereocenter but are achiral because they have a plane of symmetry
What does stereocenter mean?
A carbon atom with four different groups attached
What does optically active mean?
A molecule that can rotate plane polarized light
- chiral molecules are optically active
- achiral molecules are optically inactive
What does diastereomers mean?
Stereoisomers that are not mirror images of each other. Like a hand and foot - similar but not identical
What does racemic mixture mean?
50:50 mixture of two chiral enantiomers. 0 degrees optical activity - cancel each other out - a racemic mixture is optically inactive
What does a tetrahedral representation look like?
Looks like a pyramid with a line coming out the top
What does a Fischer Projection look like?
- |- it looks like a T with the top and bottom being pointed away from you and the left and right coming towards you
What does a stereocenter look like in a compound?
When a carbon is attached to 4 different groups
- 2 - butanol
What does a compound look like if it is optically active?
An optically active compound has a chiral center, meaning it has a carbon atom bonded to four different groups, making it able to rotate plane-polarized light.
How do you assign a priority order and determine R-S configuration
Atoms directly attached to stereocenter are ranked based on atomic number. Higher atomic number the higher the priority. Lowest priority is away from you. If groups are clockwise the configuration is R and if they read counterclockwise the configuration is S
How do you draw the enantiomer of a compound?
Do the mirror images of whatever your starting compound is
What do 2 identical isomers look like?
Alanine:
- (R)-alanine
- (S)-alanine
What do two enantiomers look like?
Alanine:
- (R)-alanine
- (S)-alanine
What do 2 diastereomers look like?
- (R,R)-2,3-dibromobutane and (R,S)-2,3-dibromobutane are diastereomers.
- They have the same molecular formula and sequence of bonded atoms but differ in the spatial arrangement around one of the chiral centers.
How do you determine how many stereoisomers are possible in a structure?
Stereoisomers - 2^n
Enantiomeric pairs - 2^n-1
What is the meaning of stereoisomers?
Isomers with the same order of attachment of atoms but a different orientation of their atoms in space
What’s the relationship with rotation in enantiomers and diastereomers?
Different. Enantiomers rotate light equally in opposite directions, while diastereomers have different optical activities.
How do you tell the stereochemistry of products?
Achiral - reactants that form chiral products produce both enantiomers in equal amounts
Chiral - the original stereochemistry remains the same
- the new stereocenter can be R or S making diastereomers
- Diastereomers are not formed in equal amounts
