Chirality Lecture Notes

Flashcards about Chirality: The Handedness of Molecules.

What is chirality?

The handedness of molecules; a chiral object cannot be superposed on its mirror image.

Define a chiral object.

An object that cannot be superposed on its mirror image.

What are enantiomers?

Mirror images of a chiral molecule or ion; also known as optical isomers.

Define isomers.

Different compounds that have the same molecular formula.

What are stereoisomers?

Isomers with atoms of the same connectivity that differ only in the orientation of the atoms in space.

What are enantiomers?

Stereoisomers that are nonsuperimposable mirror images of each other.

What are diastereomers?

Stereoisomers that are not mirror images of each other.

What are cis-trans isomers?

Stereoisomers that result from restricted rotation about chemical bonds, such as in rings or double bonds.

What are constitutional isomers?

Compounds that have the same molecular formula but different connectivity.

Define stereoisomers.

Compounds with the same molecular formula and connectivity, but different three-dimensional spatial arrangement of their atoms.

What is the relationship between a molecule and its mirror image if they are superposable?

They are identical, and there is no possibility of enantiomerism; the object is achiral.

What is a plane of symmetry?

If a molecule possesses a plane of symmetry, it will not be chiral.

What is a stereocenter?

A carbon atom with four different groups bonded to it, which is the most common cause of enantiomerism in organic molecules.

What is the R,S system used for?

Distinguishing enantiomers by name by adding the prefix R or S to the IUPAC name.

What is the basis for assigning priority in the R,S system?

Atomic number; the higher the atomic number, the higher the priority.

How do you assign R or S configuration?

Orient the molecule with the lowest priority group away, then read the other groups from highest to lowest priority. Clockwise is R, counterclockwise is S.

What is the maximum number of possible stereoisomers for a molecule with n stereocenters?

2^n

Define diastereomers.

Stereoisomers that are not mirror images of each other.

What is the difference between enantiomers and diastereomers?

Enantiomers are nonsuperimposable mirror images, while diastereomers are stereoisomers that are not mirror images.

Define ordinary light.

Light waves vibrating in all planes perpendicular to its direction of propagation.

Define plane-polarized light.

Light waves vibrating only in parallel planes.

What is a polarimeter?

An instrument for measuring the ability of a compound to rotate the plane of plane-polarized light.

What does it mean when a compound is optically active?

It is capable of rotating the plane of plane-polarized light.

What is a dextrorotatory?

Clockwise rotation of the plane of plane-polarized light, indicated by (+).

What is a levorotatory?

Counterclockwise rotation of the plane of plane-polarized light, indicated by (-).

What is specific rotation?

The observed rotation of an optically active substance at a concentration of 1 g/mL in a sample tube 10 cm long.

What is a racemic mixture?

A 50:50 mixture of two enantiomers that causes no net rotation of plane-polarized light.

Are most molecules in living systems chiral?

Yes, except for inorganic salts and a few low-molecular-weight organic substances.

How do chiral molecules interact with each other?

Two members of the enantiomer pair (chiral) react differently with other chiral molecules.

Why do a molecule and its enantiomer elicit a different physiological response?

Because interactions between molecules in living systems take place in a chiral environment.