Stereogenic Centers
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Questions and Answers

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?

  • 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?

  • 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?

    <p>H</p> Signup and view all the answers

    How are priorities assigned to two identical atoms bonded to the stereogenic center?

    <p>Based on the atomic number of the atoms bonded to these atoms</p> Signup and view all the answers

    What is the purpose of the IUPAC name in the Cahn-Ingold-Prelog system?

    <p>To provide a base name for the enantiomer</p> Signup and view all the answers

    What is the direction of the circle tracing to assign R to a stereogenic center?

    <p>Clockwise</p> Signup and view all the answers

    How many stereoisomers are possible for a compound with two stereogenic centers?

    <p>4</p> Signup and view all the answers

    What is the term used to describe a molecule with two stereogenic centers that may or may not be chiral?

    <p>Diastereomers</p> Signup and view all the answers

    What is the formula to calculate the maximum number of stereoisomers for a compound with n stereogenic centers?

    <p>2^n</p> Signup and view all the answers

    What is the result of tracing the circle in a counterclockwise direction when assigning R or S to a stereogenic center?

    <p>The isomer is named S</p> Signup and view all the answers

    How many stereoisomers are possible for a compound with one stereogenic center?

    <p>2</p> Signup and view all the answers

    What is the order of priority of groups in 2-butanol?

    <p>–OH (1), –CH2CH3 (2), –CH3 (3), and –H (4)</p> Signup and view all the answers

    According to Rule 3, what is the order of priority among isotopes of hydrogen?

    <p>In order of decreasing mass number</p> Signup and view all the answers

    How is a multiply bonded atom treated in assigning priority?

    <p>As an equivalent number of singly bonded atoms</p> Signup and view all the answers

    What is the first step in assigning R or S to a stereogenic center?

    <p>Assigning priorities from 1 to 4 to each group</p> Signup and view all the answers

    What is the purpose of rotating the remaining three groups in assigning R or S?

    <p>To place the lowest priority group in the down position</p> Signup and view all the answers

    What is the Fischer projection used for in stereogenic centers?

    <p>To display enantiomers</p> Signup and view all the answers

    What is the property of a meso compound?

    <p>It is optically inactive</p> Signup and view all the answers

    What is the characteristic of a molecule with a plane of symmetry?

    <p>It cannot be optically active</p> Signup and view all the answers

    What is the relationship between VII and VIII?

    <p>VII is superimposable on VIII</p> Signup and view all the answers

    Why is VII not optically active?

    <p>It is a meso compound</p> Signup and view all the answers

    What is the characteristic of a molecule with stereogenic centers?

    <p>It can be optically active or inactive</p> Signup and view all the answers

    Why can we recognize a meso structure on sight?

    <p>Because one half of the molecule is the mirror image of the other half</p> Signup and view all the answers

    What is the relationship between structures I and II?

    <p>They are diastereomers</p> Signup and view all the answers

    What is the characteristic of structure III compared to I and II?

    <p>It is not superimposable on either I or II</p> Signup and view all the answers

    What is the relationship between structures III and IV?

    <p>They are enantiomers</p> Signup and view all the answers

    What is the characteristic of compound IV?

    <p>It is a diastereomer of both I and II</p> Signup and view all the answers

    How many stereoisomeric forms does 2,3-dichlorobutane exist in?

    <p>Four</p> Signup and view all the answers

    What is the result of finding the mirror image of structure III?

    <p>It is not superimposable on III</p> Signup and view all the answers

    A molecule with stereogenic centers is always chiral.

    <p>False</p> Signup and view all the answers

    A meso compound can exist in two enantiomeric forms.

    <p>False</p> Signup and view all the answers

    A molecule with a plane of symmetry is always optically active.

    <p>False</p> Signup and view all the answers

    VII and VIII are enantiomers of each other.

    <p>False</p> Signup and view all the answers

    A molecule with stereogenic centers is always optically active.

    <p>False</p> Signup and view all the answers

    A meso compound has a plane of symmetry.

    <p>True</p> Signup and view all the answers

    VII is a chiral molecule.

    <p>False</p> Signup and view all the answers

    A molecule with a plane of symmetry is always chiral.

    <p>False</p> Signup and view all the answers

    VIII is a diastereomer of VII.

    <p>False</p> Signup and view all the answers

    A molecule with stereogenic centers can exist in multiple stereoisomers.

    <p>True</p> Signup and view all the answers

    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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    Stereogenic Centers PDF

    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!

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