Chirality and Stereoisomers

A comprehensive set of flashcards covering concepts of chirality, stereoisomerism, and sugars as discussed in the lecture.

What are enantiomers?

A set of chiral molecules that are mirror images of each other and cannot be superimposed.

What distinguishes stereoisomers from structural isomers?

Stereoisomers have the same connectivity but differ in the spatial arrangement of atoms, while structural isomers differ in connectivity.

How are structural isomers formed?

By disconnecting a group from one carbon atom and reconnecting it to another atom.

What is the key requirement for a molecule to be chiral?

It must have four different groups bonded to the same carbon atom.

What is a geometric isomer?

A type of stereoisomer that arises when there is a double bond in the molecule.

What is the difference between chiral and achiral molecules?

Chiral molecules cannot be superimposed on their mirror images, while achiral molecules can.

What is polarized light?

Light that oscillates in a single plane, as opposed to non-polarized light which oscillates in multiple planes.

What effect do enantiomers have on polarized light?

Enantiomers rotate the plane of polarized light in opposite directions: one clockwise and the other counterclockwise.

What prefix is used to distinguish between types of stereoisomers with a chiral carbon?

The prefixes 'D' and 'L' are used.

What is a monosaccharide?

The smallest structure that can be called a sugar or carbohydrate, which cannot be hydrolyzed into simpler sugars.

What does ‘polyhydroxy’ refer to in sugars?

It refers to having multiple hydroxyl (–OH) groups.

What distinguishes aldoses from ketoses?

Aldoses contain an aldehyde functional group, while ketoses contain a ketone functional group.

What is the Fischer projection?

A way of representing the three-dimensional structure of monosaccharides using intersecting lines.

How do chiral carbons appear in Fischer projections?

Chiral carbons are represented by intersecting lines, indicating different groups attached to the carbon.

What is the significance of the 'D' and 'L' designations in sugars?

They indicate the position of the hydroxyl group on the last chiral carbon in the structure.

What are diastereomers?

Stereoisomers that are not mirror images of each other and cannot be superimposed.

How can you tell if two molecules are enantiomers or diastereomers?

Compare the groups on the chiral carbons; if all are the same, they are enantiomers; if any one differs, they are diastereomers.

What is the structural formula of glucose?

C6H12O6, consisting of six carbon atoms, twelve hydrogen atoms, and six oxygen atoms.

At what carbon position does a ketone appear in a ketose?

At the second carbon position.

How do you identify an aldose?

By the presence of an aldehyde functional group at the end of the carbon chain.

Why do we use Fischer projections instead of drawing three-dimensional molecules?

Fischer projections simplify drawing complex organic molecules while still representing their connectivity accurately.

What happens when monosaccharides dissolve in water?

They can undergo intramolecular reactions to form ring structures.

How is chirality related to biological molecules?

All biological sugars are of the D- and L- form; chirality plays a critical role in biochemical interactions.

What does the presence of multiple chiral centers allow in terms of isomers?

It allows for the existence of diastereomers.

What characterizes a diastereomer compared to an enantiomer?

Diastereomers have more than one chiral center and are not mirror images of each other.

What is the role of a carbonyl group in sugars?

It determines whether the sugar is an aldose (aldehyde) or a ketose (ketone).

Explain what a D-sugar is.

A sugar whose hydroxyl group on the last chiral carbon is on the right side in its Fischer projection.

Explain what an L-sugar is.

A sugar whose hydroxyl group on the last chiral carbon is on the left side in its Fischer projection.

Which sugar is referred to as a pentose?

A monosaccharide with five carbon atoms.

Which sugar is referred to as a hexose?

A monosaccharide with six carbon atoms.

What misconception might one have regarding the naming of sugars?

That the name of the sugar indicates its chirality, when in fact it does not specify D or L form.

What can be inferred if two sugars are both D-galactose and L-galactose?

They are enantiomers of each other.

What is the result of having identical groups around a chiral center?

The molecule becomes achiral and cannot form stereoisomers.

Why are sugars classified as chiral?

Because they often have multiple chiral centers.

What notation is used for a five-carbon sugar?

Pentose.

What notation is used for a six-carbon sugar?

Hexose.

What type of carbon cannot be chiral?

A carbon involved in a double bond or with two identical groups.

How do molecular models help in understanding chirality?

They visually represent the 3D arrangement of atoms in a molecule.

What defines the reactivity of sugars in biological systems?

The presence and arrangement of functional groups like hydroxyl and carbonyl.

Why is understanding stereoisomers important in biochemistry?

Different stereoisomers can have vastly different biological activities and effects.

How can stereoisomers affect drug design?

Stereoisomers can have different affinities and specificities for biological receptors, influencing drug efficacy.

What is the significance of the ‘cis’ and ‘trans’ prefixes?

They refer to the geometric arrangement of groups around double bonds in stereoisomers.

Why is it critical to recognize the distinction between D and L forms of sugars?

Because the biological activity of sugars can depend on their specific stereoisomer.

What do we refer to as an achiral molecule?

A molecule that possesses symmetry and can be superimposed on its mirror image.