OChem Ch 5 Stereochemistry part 1 (enantiomer, chiral, achiral, stereoisomer)

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mikepl103
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OChem Ch 5 Stereochemistry part 1 (enantiomer, chiral, achiral, stereoisomer)
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2013-11-10 18:05:18
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OChem Stereochemistry part enantiomer chiral achiral stereoisomer
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OChem Ch 5 Stereochemistry part 1 (enantiomer, chiral, achiral, stereoisomer)
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  1. what is a chiral carbon?
    tetrahedral carbons with 4 different attached groups are chiral
  2. when assigning (R) and (S) configurations to molecules that contain chiral carbons, the arrow that goes from lowest priority to highest priority in the (R) configuration goes ____ and the arrow goes ______ in the (S) configuration.
    • (R)- clockwise
    • (S)- counterclockwise
  3. What are the Cahn-Ingold-Prelog rules?
    1. Assign a priority number to each group attached to the chiral carbon.

    2. Atom with highest atomic number assigned the highest priority number.

    3. In the case of ties, look at the next atoms along the chain.

    4. Double and triple bonds are treated like bonds to duplicate atoms.
  4. if a molecule has an internal mirror of plane, is it chiral or achiral?
    it has to be achiral
  5. if a molecule doesn't have an internal mirror of plane, is it chiral or achiral?
    it can be either one
  6. what is a racemic mixture?
    a mixture of equal quantities of the d- and l-enantiomers of a molecule.
  7. what are the properties of a racemic mixture?
    no optical activity and the mixture may have different bp and mp from the enantiomers
  8. if optically inactive reagents combine to form a chiral molecule, what is formed?
    a racemic mixture is formed
  9. to determine if a confrmationally mobile molecule can be optically active, you must do what?
    consider it's most symmetric conformation
  10. if a molecule is at equilibrium with it's mirror image, is it chiral?
    no
  11. what is an allene?
    compounds that contain the C=C=C unit
  12. what are some quick rules of thumb in order to determine if a molecule is chiral/achiral?
    1)check if it has an internal mirror plane. If it does it is definitely achiral. If it doesn't it can be either chiral or achiral.

    • 2) check to see if it has chiral centers:
    •     -if it has one, it is chiral.
    •     -if it has more than one, it can be either chiral or achiral
    •     -if it has none, it is unlikely, but possible, for it to be chiral

    3)if the molecule is planar, then it is achiral (be careful with this rule because some molecules that appear planar may actually not be planar)

    4) If a molecule is sterically hindered such that there is no equilibrium between it's conformations, it is chiral 

    • ex. 

    5) if an allene (a molecule that contains C=C=C) has two different groups attached to each end, it is chiral

    6) if you are presented with a fischer projection or you can easily make a fischer projection of the molecule that you are trying to determine as either chiral or achiral, then make a mirror image of the fischer projection, rotate the mirror image 180 degrees, and see it lines up with the original molecule. If it doesn't your molecule is chiral

    7) if the molecule that you are examining is a ring and it contains two heteroatoms that are anti- and opposite each other, the molecule is likely achiral.

    • ex.
  13. if an optically active molecule roates the plane polarized light clockwise, then it is labeled as ___ or ____
    (+) or (d)
  14. if an optically active molecule rotates plane polarized light counterclock., it is labeled as ___ or ___
    (-) or (l)
  15. in a fischer projection, vertical lines represent ___ _____
    dashed lines

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