1.) Identify and define constitutional and stereoisomers.
Constitutional: Two compounds have the same formula but different atom connections. Different chemical and physical properties.
Example: n-butane and isobutane.
Stereoisomers: Isomers with the same order of attachment of atoms in their molecules but a different orientation of their atoms or groups in space. For more, see part 2.
2.) Give examples of the following concepts.
Stereocentre: Molecules that contain a stereocentre are non-super imposable with their mirror image. No plane of symmetry. 4 different substituents attached to it. A molecule must me chiral to have a stereocentre, therefore stereostructures must be enantiomers.
Stereoisomers are divided into two groups:
Enantiomers: Mirror images. Non-super imposable with its mirror image, or no plane of symmetry (chiral). Enantiomers have identical physical and chemical properties, except for: the degree of rotation of plane polarized light and the interaction of each enantiomer with another chiral molecule. Chiral: No plane of symmetry, Achiral: Plane of symmetry.
So the requirements for molecular chirality is a carbon atom with 4 different constituents that is non superimposable with its mirror image.
Diastereomers: Not mirror images
Racemate: A mixture of both enantiomers. Also called a racemic mixture. Racemates do not rotate plane polarized light.
Meso Compound: A compound that contains stereocentres but is achiral (still has a plane of symmetry).
Optical Rotation: Plane of polarized light passes through a solution of a molecule containing a stereocentre, the light is rotated. This rotation is measured using a polarimeter. Direction of rotation is either + or -.
3.) Determine whether an object or molecule is chiral.
For definitions see above.
4.) Identify stereocentres in molecules given the molecular structure.
5.) Define the relationship between stereoisomers as either enantiomeric or diastereomeric.
Enantiomers are stereoisomers that are mirror images. A pair of enantiomers are mirror image forms of the same compound and have opposite absolute stereochemistry. Diastereomers are stereoisomers that are not mirror images. Different relative stereochemistry.
6.) Given a molecular structure, determine all possible stereoisomers.
Molecules that have one stereocentre have two stereoisomers. For molecules that have more than one stereocentre, there are potentially 2^n stereoisomers. Where n is the number of stereocentres. For a molecule with two sterocentres, there are 4 stereoisomers: 2 pairs of mirror images, 2 pairs of not mirror images, therefore two pairs of enantiomers and two pairs of diastereomers.
7.) Apply a sequence of rules (Cahn-Ingold-Prelog) to determine the absolute stereochemistry of a stereocentre.
i.) Assign priorities to the four atoms directly attached to the stereogenic centre. The atom with the highest atomic number is 1 and the lowest atomic number is 4. ii.) If priority cant be decided by step one (two molecules are the same). Then continue to the third and fourth atoms until a point of difference is reached. iii.) The group with the lowest priority should be pointed away from the viewer. iv.) The direction of rotation of the groups ranked 1,2,3 now determines the configuration.
v.) If the direction of rotation is clockwise (R) vi.) If the direction of rotation is anti-clockwise (S)
8.) Demonstrate understanding of the importance of chirality in biological systems.
A single enantiomer will interact with another chiral molecule in a difference manner to its mirror image. A receptor that rejects some enantiomers is the key to why each pair of enantiomeric drugs may have a different biological effect. Useful when a drug is administered as a racemate.
9.) Determine whether stereoisomerism is possible for a given alkene.
If one CH group of