Chapter 5
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Questions and Answers

What tragic consequence was linked to the use of Thalidomide in pregnant women?

  • Development of severe birth defects (correct)
  • Enhanced cognitive development in children
  • Increased chances of multiple births
  • Higher rates of successful pregnancies

    • Which characteristic indicates that a molecule is non-chiral?

  • Possession of a plane of symmetry (correct)
  • Absence of stereoisomers
  • Two distinct enantiomers
  • Presence of a chiral center

    • Why is it problematic for enantiomers to share the same IUPAC name?

  • It eliminates the need for distinct drug regulations.
  • It complicates the process of drug synthesis.
  • It can lead to confusion in clinical settings. (correct)
  • It reduces molecular diversity in chemical nomenclature.

    • What is the main structural feature that differentiates enantiomers?

    <p>The arrangement of atoms around a chiral center</p> Signup and view all the answers

    Which enantiomer of Thalidomide is associated with therapeutic effects?

    <p>The enantiomer that alleviates morning sickness</p> Signup and view all the answers

    How can a plane of symmetry be defined in a molecule?

    <p>As a line dividing the molecule that results in identical halves</p> Signup and view all the answers

    When was the link between Thalidomide and birth defects discovered?

    <p>In the year 1963</p> Signup and view all the answers

    What is an outcome of all molecules having a plane of symmetry?

    <p>They are classified as achiral.</p> Signup and view all the answers

    What does the R,S system help in the context of enantiomers?

    <p>It assigns distinct names to enantiomers.</p> Signup and view all the answers

    What is the first step in assigning the (R) and (S) configurations at a stereocenter?

    <p>Assign priorities based on atomic numbers.</p> Signup and view all the answers

    If two atoms directly attached to a chirality center have the same atomic number, what should you do next?

    <p>Examine the next set of atoms in the unassigned groups.</p> Signup and view all the answers

    What does a clockwise path from highest to lowest priority indicate at an asymmetric carbon?

    <p>The configuration is (R).</p> Signup and view all the answers

    When determining the priority of groups containing double or triple bonds, how should you assess the atoms involved?

    <p>Count the atoms as if they were duplicated or triplicated.</p> Signup and view all the answers

    What should you do if the lowest priority group is not pointing away from you during configuration assignment?

    <p>Change the view and rotate the molecule accordingly.</p> Signup and view all the answers

    What would be an appropriate action if two groups attached to a stereocenter have the same atomic number and are linked to another set of atoms?

    <p>Break down the next level of atoms for priority assignment.</p> Signup and view all the answers

    Which of the following is the correct order of operations when assigning (R) and (S) configurations?

    <p>Assign priorities, visualize molecule, trace a path.</p> Signup and view all the answers

    Which configuration corresponds to a counter-clockwise path tracing from highest to lowest priority?

    <p>(S)</p> Signup and view all the answers

    After determining a molecule's configuration, what should you confirm regarding the bonded atoms?

    <p>The highest priority atom must always be directly bonded.</p> Signup and view all the answers

    In the example of (2-Butanol), which of the following configurations is indicated if the path is clockwise?

    <p>(R)-2-Butanol</p> Signup and view all the answers

    Which pairs of compounds are classified as enantiomers?

    <p>Compounds I and II</p> Signup and view all the answers

    What characteristic prevents compounds III and IV from being classified as enantiomers?

    <p>They are identical to each other.</p> Signup and view all the answers

    Which statement correctly describes diastereomers among the given compounds?

    <p>Compounds I and III, II and III are diastereomers.</p> Signup and view all the answers

    What is the relationship between compounds I and III?

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

    Which of the following is a correct full name for a compound with the configuration (2R, 3R)?

    <p>(2R, 3R)-2,3-Dibromobutane</p> Signup and view all the answers

    What configuration is specified for the C2 chiral center in 2,3-Dibromobutane?

    <p>R configuration</p> Signup and view all the answers

    In naming compounds with multiple chirality centers, which aspect is crucial for determining configurations?

    <p>Looking through specific bonds</p> Signup and view all the answers

    How many stereoisomers exist for the given compounds?

    <p>Three stereoisomers</p> Signup and view all the answers

    Which is true about the configuration of C2 in the compound?

    <p>C2 can be either R or S.</p> Signup and view all the answers

    Which statement accurately describes cis-1,3-dimethylcyclohexane?

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

    What is true regarding 1,3-dimethylcyclohexane and its stereoisomers?

    <p>There are three stereoisomers overall, including meso form.</p> Signup and view all the answers

    How do trans-1,2-dimethylcyclohexane and cis-1,2-dimethylcyclohexane relate to enantiomers?

    <p>Both forms exist as pairs of enantiomers.</p> Signup and view all the answers

    What characteristic distinguishes trans-1,3-dimethylcyclohexane from cis-1,3-dimethylcyclohexane?

    <p>Trans form is achiral while cis is chiral.</p> Signup and view all the answers

    Which of the following statements about 1,4-dimethylcyclohexane is correct?

    <p>Both cis- and trans-1,4-dimethylcyclohexane are achiral.</p> Signup and view all the answers

    What occurs in the interconversion of (II) and (III) of 1,2-dimethylcyclohexane?

    <p>This transformation involves a rotation along the vertical axis.</p> Signup and view all the answers

    What percentage of enantiomeric excess does an enantiomerically pure sample achieve?

    <p>100%</p> Signup and view all the answers

    What would be the observed specific rotation of a sample of (S)-(+)-2-butanol containing an equimolar amount of (R)-(–)-2-butanol?

    <p>0%</p> Signup and view all the answers

    How can enantiomeric excess be calculated from optical rotations?

    <p>Using the formula % enantiomeric excess = observed specific rotation / specific rotation of pure enantiomers</p> Signup and view all the answers

    If a mixture of (S)-(+)-2-butanol shows a specific rotation of +6.76, what is the specific rotation of a completely racemic mixture?

    <p>0</p> Signup and view all the answers

    Which of the following statements is true regarding a sample of (S)-(+)-2-butanol that shows a specific rotation between 0 and +13.52?

    <p>It has an enantiomeric excess less than 100%.</p> Signup and view all the answers

    Which of the following statements best describes enantiomeric excess (ee)?

    <p>It is a measure of the optical purity of an enantiomer.</p> Signup and view all the answers

    In the example, how is the enantiomeric excess of the (S)-(+)–2-butanol calculated when the specific rotation is +6.76?

    <p>It is calculated by dividing +6.76 by the specific rotation of pure enantiomers.</p> Signup and view all the answers

    Which statement correctly describes the specific rotation of an enantiomerically pure sample of (S)-(+)–2-butanol?

    <p>It equals +13.52.</p> Signup and view all the answers

    What is the specific rotation of the achiral molecules discussed in the synthesis of chiral molecules?

    <p>0</p> Signup and view all the answers

    When a specific rotation of a sample is known, how can one piece together the enantiomeric ratio?

    <p>By using the specific rotation values of both enantiomers.</p> Signup and view all the answers

    Study Notes

    Chirality in Drugs

    • Thalidomide was used to treat morning sickness in pregnant women, but it was later discovered that it caused serious birth defects.
    • Thalidomide is a chiral molecule and its enantiomers have different effects. The (R)- enantiomer is effective in treating morning sickness, while the (S)-enantiomer causes serious birth defects.

    Testing for Chirality: Planes of Symmetry

    • A molecule is achiral (not chiral) if it possesses a plane of symmetry.
    • A plane of symmetry is an imaginary plane that bisects a molecule so that the two halves are identical mirror images.

    Naming Enantiomers: The R,S-System

    • The R,S-system is used to name enantiomers.
    • Rule 1: Assign priorities to the four groups attached to the chirality center based on atomic number, higher atomic number = higher priority.
    • Rule 2: If priorities cannot be assigned based on atomic number of the atoms directly attached to the chirality center, then the next set of atoms are examined until a decision can be made.
    • Rule 3: Visualize the molecule with the lowest priority group pointing away from you, then trace a path from highest to lowest priority. If the path is clockwise, the configuration is (R); if the path is counterclockwise, the configuration is (S).
    • Rule 4: For groups containing double or triple bonds, assign priorities as if both atoms were duplicated or triplicated.

    Racemic Forms and Enantiomeric Excess

    • An enantiomerically pure sample contains only one enantiomer and has an enantiomeric excess of 100%.
    • Enantiomeric excess (ee) is also known as optical purity and can be calculated from the optical rotation of a mixture.
    • The formula for enantiomeric excess is: 
      % enantiomeric excess = (observed specific rotation / specific rotation of the pure enantiomer) x 100

    Synthesis of Chiral Molecules

    • A racemic mixture is a 50:50 mixture of enantiomers.
    • The synthesis of chiral molecules often produces a racemic mixture, but sometimes, a single enantiomer can be obtained through a chiral catalyst.
    • If two chiral centers are present, it is possible to have more than two stereoisomers:
      • Enantiomers are non-superimposable mirror images.
      • Diastereomers are stereoisomers that are not enantiomers.
      • Meso compounds are achiral molecules with chiral centers.

    Fischer Projection Formulas

    • Fischer projection formulas are a way of representing three-dimensional molecules in two dimensions.
    • In Fischer projections, horizontal bonds point out of the plane and vertical bonds point into the plane.
    • Cyclohexane can exist as cis and trans isomers.
    • 1,4-Dimethylcyclohexane does not have a plane of symmetry, and the cis and trans forms are diastereomers.
    • 1,3-Dimethylcyclohexane has a plane of symmetry when in the cis conformation and it is a meso compound.
    • The trans conformation of 1,3-dimethylcyclohexane has no plane of symmetry and exists as two enantiomers.
    • 1,2-Dimethylcyclohexane exists as two enantiomers; both cis and trans configurations result in enantiomers.

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    Stereochemistry: Chiral Molecules PDF

    Description

    Explore the crucial role of chirality in drug effectiveness, particularly focusing on thalidomide's enantiomers and their contrasting effects. Understand the concepts of achirality, planes of symmetry, and the R,S-system for naming enantiomers. This quiz delves into the complexities of molecular structures that impact pharmacology.

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