Fischer Projections and R/S Nomenclature in Stereochemistry

Who developed the Fischer projection system?

Emil Fischer

What is the purpose of a Fischer projection?

To represent chiral carbons in two dimensions.

What shape does the shadow of a chiral carbon cast in a Fischer projection?

A cross.

In a Fischer projection, where is the chiral carbon assumed to be located?

On the plane of the paper.

What do horizontal bonds represent in a Fischer projection?

Bonds that come out of the plane of the paper towards the viewer.

What do vertical bonds represent in a Fischer projection?

Bonds that go behind the plane of the paper away from the viewer.

How is the carbon chain represented in a Fischer projection?

As a vertical line.

What is a key consideration when assigning R/S configuration from a Fischer projection?

The position of the lowest priority group.

What happens if the lowest priority group is on a horizontal bond in a Fischer projection?

The configuration obtained is the opposite of the actual one.

What notation is used to indicate configurations at chiral carbons?

IUPAC notation.

What is the configuration of a chiral carbon if the priority order is clockwise?

It is (R) if the lowest priority group is vertical.

What is the configuration of a chiral carbon if the priority order is counterclockwise?

It is (S) if the lowest priority group is vertical.

What does flipping a Fischer projection over do to the configuration?

It changes the configuration of the central carbon to the opposite.

Can you rotate a Fischer projection by 90 degrees without changing the configuration?

No, it changes the configuration.

What happens if you rotate a Fischer projection by 180 degrees?

The configuration remains unchanged.

What is the significance of the D-(+)-glucose molecule in Fischer projections?

It illustrates the convention of vertical arrangement of the main carbon chain.

How should chiral centers be handled when assigning configurations in molecules with multiple chiral centers?

Isolate each chiral center and deal with them one at a time.

What is the implication of having hydrogen atoms along horizontal lines in Fischer projections?

It can affect the assignment of R/S configuration.

What is the visual representation of chiral and achiral molecules in Fischer projections?

Chiral molecules lack planes of symmetry, while achiral molecules have them.

What is the most common context for using Fischer projections?

Carbohydrates and large biological molecules.

What is the role of the lowest priority group in determining the configuration?

It should ideally be placed on a vertical bond to simplify the process.

How can you represent the same (S) isomer in different Fischer formulas?

By rearranging the groups while maintaining the same connectivity.

What does the term 'chiral carbon' refer to?

A carbon atom bonded to four different substituents.

What is the main advantage of Fischer projections?

They provide a convenient way to represent complex molecules on paper.

What is the first step in assigning configuration to a chiral center?

Identify the chiral carbon and assign priorities to the groups attached.

What does the term 'achiral' mean in the context of Fischer projections?

A molecule that has a plane of symmetry and cannot exist as enantiomers.

What is the relationship between Fischer projections and 3D representations?

Fischer projections can be translated into 3D representations while maintaining configuration.

What is chirality in molecules?

Chirality refers to a property of a molecule that makes it non-superimposable on its mirror image.

What happens when two groups attached to a chiral carbon are exchanged?

Exchanging any two groups changes the configuration of the chiral center.

How can you determine if two Fischer projections represent the same molecule?

If one exchange suffices to transform one into the other, they are enantiomers; if two exchanges are required, they are the same molecule.

What relationship exists between chiral mirror images?

Chiral mirror images are called enantiomers.

What is a cyclic permutation in stereochemistry?

A cyclic permutation is a rotation of three bonds around a chiral carbon while holding one bond steady, leaving the configuration unchanged.

What defines meso forms in molecules?

Meso forms contain two or more chiral centers and at least one plane of symmetry, making them achiral.

Can meso forms have enantiomers?

No, meso forms cannot have enantiomers because they are identical to their mirror images.

What are diastereomers?

Diastereomers are stereoisomers that are not mirror images of each other.

What is the relationship between cis/trans isomers and diastereomers?

Cis/trans isomers are always diastereomers.

What is the maximum number of stereoisomers for a molecule with n chiral centers?

The maximum number of stereoisomers is 2^n.

What is the stereochemical relationship of (2R, 3R)-2,3-dibromobutane and (2S, 3S)-2,3-dibromobutane?

They are enantiomers.

What is the stereochemical relationship of (2R, 3R)-2,3-dibromobutane and meso-2,3-dibromobutane?

They are diastereomers.

What is the significance of a plane of symmetry in stereochemistry?

A plane of symmetry indicates that a molecule is achiral and can be superimposed on its mirror image.

What is the relationship between the configurations of enantiomers?

Enantiomers have opposite configurations at all chiral centers.

How do you identify diastereomers in a pair of molecules?

Diastereomers differ in configuration at one or more chiral centers but not all.

What is the relationship between the two structures shown: CH3-CH(Br)-CH2-CH3 and CH3-CH(Cl)-CH2-CH3?

They are diastereomers due to different configurations at the chiral center.

What is the relationship between the two structures shown: CH3-CH(Br)-CH2-CH3 and CH3-CH(Br)-CH2-CH3?

They are the same compound.

What is the relationship between the two structures shown: CH3-CH(Cl)-CH2-CH3 and CH3-CH(Cl)-CH2-CH3?

They are the same compound.

What is the significance of geometric isomers in stereochemistry?

Geometric isomers are a subcategory of diastereomers that differ in the arrangement of groups around a double bond or ring structure.

What is the relationship between the configurations of the two molecules with two chiral centers?

If they are mirror images, they are enantiomers; if not, they are diastereomers.

What does the term 'achiral' refer to?

Achiral refers to molecules that can be superimposed on their mirror images.

What is the relationship between the two structures shown: CH3-CH(Br)-CH2-CH3 and CH2Br-CH(CH3)-CH3?

They are enantiomers.

What is the relationship between the two structures shown: CH3-CH(Cl)-CH2-CH3 and CH3-CH(Br)-CH2-CH3?

They are diastereomers.