Stereochemistry concepts (R/S, E/Z, chirality) and reaction mechanism steps taught in a college organic chemistry sequence.
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- What is a chiral center?
- An atom (usually carbon) bonded to four different groups
- How many stereoisomers does a molecule with one chiral center have?
- Two (one pair of enantiomers)
- Define enantiomers
- Non-superimposable mirror images that rotate plane-polarized light in opposite directions
- Define diastereomers
- Stereoisomers that are not mirror images of each other
- What does R/S nomenclature describe?
- The three-dimensional spatial orientation around a chiral center
- What is the first step in assigning R or S configuration?
- Rank the four groups by atomic number using Cahn-Ingold-Prelog rules
- After ranking groups 1-2-3, which direction means R configuration?
- Clockwise (when group 4 points away)
- After ranking groups 1-2-3, which direction means S configuration?
- Counterclockwise (when group 4 points away)
- Define a meso compound
- A molecule with multiple chiral centers that is achiral due to an internal plane of symmetry
- In a Fischer projection, what do horizontal bonds represent?
- Bonds projecting forward toward the viewer (wedge bonds)
- In a Fischer projection, what do vertical bonds represent?
- Bonds pointing backward away from the viewer (hash bonds)
- What is the E/Z nomenclature used for?
- Describing the geometry (cis/trans) around a double bond
- In E/Z nomenclature, what does E stand for?
- Entgegen (German for opposite); the two highest-priority groups are on opposite sides of the double bond
- In E/Z nomenclature, what does Z stand for?
- Zusammen (German for together); the two highest-priority groups are on the same side of the double bond
- What are the Cahn-Ingold-Prelog rules?
- Priority rules for assigning 1-4 to groups in R/S and E/Z nomenclature based on atomic number