page 10 Flashcards
Which types of carbon atoms cannot be stereogenic centers?
A: CH₂ and CH₃ groups, as well as any sp or sp² hybridized carbons.
What is the hybridization of carbon atoms that can form stereogenic centers?
A: sp³ hybridization, as they form tetrahedral geometries.
How does sp or sp² hybridization prevent a carbon atom from being a stereogenic center?
A: These hybridizations result in linear or planar geometries, which cannot support chirality.
Can larger organic molecules have multiple stereogenic centers?
A: Yes, they can have two, three, or even hundreds of stereogenic centers.
What does the presence of multiple stereogenic centers imply for a molecule?
A: It can exist in many stereoisomeric forms, including enantiomers and diastereomers.
How to Determine R and S Configurations:
Assign Priorities to Substituents:
Identify the four groups attached to the chiral carbon.
Assign priorities (1, 2, 3, 4) based on atomic number:
The higher the atomic number of the atom directly bonded to the chiral carbon, the higher the priority.
If two atoms are the same, move to the next bonded atoms until a difference is found.
Orient the Molecule:
Rotate the molecule so that the group with the lowest priority (4) is pointing away from you (behind the plane of the paper or screen).
Trace the Path of the Priorities:
Trace a path from priority 1 → 2 → 3 (ignoring group 4).
If the path is clockwise, the configuration is R (from Latin rectus, meaning “right”).
If the path is counterclockwise, the configuration is S (from Latin sinister, meaning “left”).
Key Points to Remember:
Double and Triple Bonds: Treat multiple bonds as if the atom is bonded to multiple equivalent single atoms. For example:
A carbon in a double bond (C=O) is treated as bonded to two oxygen atoms.
Lowest Priority Group Facing Forward: If the lowest priority group is not pointing away, the configuration you determine will be the opposite of the actual configuration.
Chirality and Optical Activity: R and S do not directly indicate whether a molecule rotates light clockwise (+) or counterclockwise (-); they only describe spatial arrangement.
Which types of carbons are never stereogenic centers?
A:
CH₂ and CH₃ groups.
Carbons with sp or sp² hybridization.
How does a plane of symmetry relate to chirality?
A:
Molecules with a plane of symmetry are achiral.
Molecules without a plane of symmetry can be chiral.
How do you determine if a molecule is chiral?
A:
If its mirror image is non-superimposable and it lacks a plane of symmetry, it is chiral.
If its mirror image is superimposable and it has a plane of symmetry, it is achiral.
Does every molecule have a mirror image?
A: Yes, every molecule has a mirror image, but the key question is whether it is superimposable on the original molecule.
How do you determine if a molecule is chiral?
A:
If its mirror image is non-superimposable and it lacks a plane of symmetry, it is chiral.
If its mirror image is superimposable and it has a plane of symmetry, it is achiral.
What is the difference between a stereogenic center and chirality?
A: A stereogenic center is a structural feature (a carbon with four different groups), while chirality is a property of the entire molecule.
What is the relationship between planes of symmetry and chirality?
A: A plane of symmetry makes a molecule achiral, as it allows for superimposability on its mirror image.
How do you assign R/S configurations?
A:
Assign priorities to the four groups attached to the stereogenic center based on atomic number.
Orient the molecule so the lowest priority group is pointing away.
Trace the path of groups 1 → 2 → 3.
Clockwise = R
Counterclockwise= s
