Podcast
Questions and Answers
What is the system of naming enantiomers with the prefixes R or S called?
What is the system of naming enantiomers with the prefixes R or S called?
- The IUPAC system
- The Cahn-Ingold-Prelog system (correct)
- The Enantiomer system
- The Stereochemical system
How are priorities assigned to the atoms directly bonded to the stereogenic center?
How are priorities assigned to the atoms directly bonded to the stereogenic center?
- In order of decreasing atomic number (correct)
- Based on the electronegativity
- Based on the molecular weight
- In order of increasing atomic number
What is the purpose of assigning priorities to the atoms bonded to the stereogenic center?
What is the purpose of assigning priorities to the atoms bonded to the stereogenic center?
- To determine the chemical properties
- To distinguish between enantiomers (correct)
- To determine the molecular weight
- To predict the reactivity
What is the lowest priority group in many molecules?
What is the lowest priority group in many molecules?
How are priorities assigned to two identical atoms bonded to the stereogenic center?
How are priorities assigned to two identical atoms bonded to the stereogenic center?
What is the purpose of the IUPAC name in the Cahn-Ingold-Prelog system?
What is the purpose of the IUPAC name in the Cahn-Ingold-Prelog system?
What is the direction of the circle tracing to assign R to a stereogenic center?
What is the direction of the circle tracing to assign R to a stereogenic center?
How many stereoisomers are possible for a compound with two stereogenic centers?
How many stereoisomers are possible for a compound with two stereogenic centers?
What is the term used to describe a molecule with two stereogenic centers that may or may not be chiral?
What is the term used to describe a molecule with two stereogenic centers that may or may not be chiral?
What is the formula to calculate the maximum number of stereoisomers for a compound with n stereogenic centers?
What is the formula to calculate the maximum number of stereoisomers for a compound with n stereogenic centers?
What is the result of tracing the circle in a counterclockwise direction when assigning R or S to a stereogenic center?
What is the result of tracing the circle in a counterclockwise direction when assigning R or S to a stereogenic center?
How many stereoisomers are possible for a compound with one stereogenic center?
How many stereoisomers are possible for a compound with one stereogenic center?
What is the order of priority of groups in 2-butanol?
What is the order of priority of groups in 2-butanol?
According to Rule 3, what is the order of priority among isotopes of hydrogen?
According to Rule 3, what is the order of priority among isotopes of hydrogen?
How is a multiply bonded atom treated in assigning priority?
How is a multiply bonded atom treated in assigning priority?
What is the first step in assigning R or S to a stereogenic center?
What is the first step in assigning R or S to a stereogenic center?
What is the purpose of rotating the remaining three groups in assigning R or S?
What is the purpose of rotating the remaining three groups in assigning R or S?
What is the Fischer projection used for in stereogenic centers?
What is the Fischer projection used for in stereogenic centers?
What is the property of a meso compound?
What is the property of a meso compound?
What is the characteristic of a molecule with a plane of symmetry?
What is the characteristic of a molecule with a plane of symmetry?
What is the relationship between VII and VIII?
What is the relationship between VII and VIII?
Why is VII not optically active?
Why is VII not optically active?
What is the characteristic of a molecule with stereogenic centers?
What is the characteristic of a molecule with stereogenic centers?
Why can we recognize a meso structure on sight?
Why can we recognize a meso structure on sight?
What is the relationship between structures I and II?
What is the relationship between structures I and II?
What is the characteristic of structure III compared to I and II?
What is the characteristic of structure III compared to I and II?
What is the relationship between structures III and IV?
What is the relationship between structures III and IV?
What is the characteristic of compound IV?
What is the characteristic of compound IV?
How many stereoisomeric forms does 2,3-dichlorobutane exist in?
How many stereoisomeric forms does 2,3-dichlorobutane exist in?
What is the result of finding the mirror image of structure III?
What is the result of finding the mirror image of structure III?
A molecule with stereogenic centers is always chiral.
A molecule with stereogenic centers is always chiral.
A meso compound can exist in two enantiomeric forms.
A meso compound can exist in two enantiomeric forms.
A molecule with a plane of symmetry is always optically active.
A molecule with a plane of symmetry is always optically active.
VII and VIII are enantiomers of each other.
VII and VIII are enantiomers of each other.
A molecule with stereogenic centers is always optically active.
A molecule with stereogenic centers is always optically active.
A meso compound has a plane of symmetry.
A meso compound has a plane of symmetry.
VII is a chiral molecule.
VII is a chiral molecule.
A molecule with a plane of symmetry is always chiral.
A molecule with a plane of symmetry is always chiral.
VIII is a diastereomer of VII.
VIII is a diastereomer of VII.
A molecule with stereogenic centers can exist in multiple stereoisomers.
A molecule with stereogenic centers can exist in multiple stereoisomers.
Study Notes
Stereogenic Centers in Organic Chemistry
- Stereogenic centers are necessary for a compound to be chiral and exhibit optical activity.
- Enantiomers are two different compounds that are non-superimposable mirror images of each other.
- The Cahn-Ingold-Prelog system is used to name enantiomers with the prefixes R or S.
Labeling Stereogenic Centers with R or S
- Assign priorities (1, 2, 3, or 4) to each group bonded to the stereogenic center.
- Use the following rules to assign priorities:
- Rule 1: Assign priorities based on the atomic number of the atoms directly bonded to the stereogenic center in decreasing order.
- Rule 2: If two atoms on a stereogenic center are the same, assign priority based on the atomic number of the atoms bonded to these atoms.
- Rule 3: If two isotopes are bonded to the stereogenic center, assign priorities in order of decreasing mass number.
- Rule 4: Treat a multiply bonded atom as an equivalent number of singly bonded atoms.
Assigning R or S to a Stereogenic Center
- Step 1: Assign priorities from 1 to 4 to each group bonded to the stereogenic center.
- Step 2: Fix one group (e.g. the highest priority group) and rotate the remaining three groups so that the lowest priority group is in the down position.
- Step 3: Trace a circle from priority group 1 to 2 to 3 to 4.
- If the circle is traced in a clockwise direction, the isomer is named R. If the circle is traced in a counterclockwise direction, the isomer is named S.
Diastereomers
- Diastereomers are stereoisomers that are not mirror images of each other.
- For n stereogenic centers, the maximum number of stereoisomers is 2n.
- When n = 1, there are 2 stereoisomers (enantiomers).
- When n = 2, there are 4 stereoisomers (2 pairs of enantiomers).
Meso Compounds
- A meso compound is one whose molecules are superimposable on their mirror images, even though they contain stereogenic centers.
- A meso compound is optically inactive.
- Meso compounds can be recognized by the fact that one half of the molecule is the mirror image of the other half.
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Description
Learn how to identify and label stereogenic centers with R or S notation, and understand the Cahn-Ingold-Prelog system for naming enantiomers. This quiz covers the prioritization of groups bonded to the stereogenic center and how to assign R or S prefixes. Test your knowledge of organic chemistry and stereoisomerism!
