Orgo 5.1-5.3

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Orgo 5.1-5.3
2013-10-14 09:20:44
CHM 201

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  1. __ is the study of the 3D structure of molecules.
    Biological systems are __, and they often discriminate between molecuels with subtle __.
    • stereochemistry
    • exquisitely selective
    • stereochemical differences
  2. What are the two broad classes.
    • constitutional (structural): differ in their bonding sequence; their atoms connect differently
    • stereoisomers: same bonding sequence, but differ in the orientation of their atoms in space
  3. Stereoisomers have different __ (4)__.
    physical, chemical and biological propertie
  4. Objects that have left-handed and right- handed forms are called __. Explain it.
    • chiral 
    • chiral objects have mirror images that are different from the original object
  5. What is an object that looks the same in the mirror?
  6. Two objects are said t be __ if they can be placed on top of each other and the 3D position of each atom of one molecule coincides with the equivalent atom of the other molecule.
  7. Nonsuperimposable mirror-image molecules are called __.
  8. A chiral compound always has an __. An achiral compound always has a mirror image that is the same as the original molecuel.
    enantiomer (a nonsuperimposable mirror image)
  9. Summary:
    • mirror-images; pairs  of compounds that are nonsuperimposable mirror images
    • chiral: different from its mirror image; having an enantiomer
    • achiral: identical with its mirror image; not chiral
  10. What makes a molecule chiral?
    the most common feature is a carbon atom that is bonded to four different groups= asymmteric carbon (or chiral carbon atom)
  11. An asymmetric carbon atom is the most common example of a __, the IUPAC term for any atom holding a set of ligands in a spatial arrangement that is not superimposable on its mirror image.
    chirality center (chiral center)
  12. __ belong to an even broader group called __, which is what?
    • chirality centers
    • stereocenters
    • any atoms at which the interchange of tow groups gives a stereoisomer
  13. __ and the __  in __ are the most common types of __.
    • asymmetric carbons
    • double-bonded carbon atoms
    • cis-trans isomers
    • stereocenters
  14. If two of the four groups on a carbon atom are the same, the arrangement is __.
    not chiral
  15. Generalize chirality, but keep in mind what.
    • that the ultimate test for chirality is always whether the molecule's mirror image is the same or diferent
    • 1) if a compound has no asymmetric carbon atom, it's usually achiral.
    • 2) if a compound has just one asymmetric carbon atom, it must be chiral
    • 3) If a compound has more than one asymmetric carbon, it may or may not be chiral
  16. internal mirror plane
    bisecting a carbon atom and its two hydrogen atoms, the part of the molecule that appears to the right of the line is the mirror image of hte part on the left
  17. Any molecule that has an __ cannot be __, even though it may contain asymmetric carbon atoms.
    • internal mirror plane of symmetry
    • chiral
  18. If a carbon atom has only three different kinds of substituents, it has an __. Therefore, it cannot contribute to __ in a molecule.
    • internal mirror plane of symmetry
    • chirality
  19. An asymmetric carbon has __ possible (mirror-image) spatial arrangments, which we call __.
    • two 
    • configurations
  20. The __ is the most widely accepted system for naming the configurations of chirality centers. Each asymmetric carbon atom is assigned a letter (R) or (S) based on its __.
    • Cahn-Ingold-Prelog convention
    • 3D configuration
  21. To determine the name, we follow a two-step procedure that assigns "__" to the four __and then assigns the name based on the __.
    • priorities
    • substituents 
    • relative positions of these substituents
  22. What is the procedure? 1.
    • assign a relative "priority" to each group bonded to the asymmetric carbon. 
    • - Look at the first atom of the group--the atom bonded to the asymmetric carbon. Atoms with higher atomic numbers receive higher priorities
  23. With different isotopes of the same element, what?
    the heavier isotopes have higher priorities
  24. What is the procedure? 1b.
    in case of ties, use the next atoms along thechain of each group as tiebreakers.
  25. What is the procedure? 1c.
    Treat = adn triple bonds as if each were a bond to a separate atom. When you break a bond, you always add two imaginary atoms
  26. What is the procedure? 2.
    using a 3D drawing or model, put the fourth priority group away from you and view the molecule with the first, second , and third priority groups radiating toward you like the spokes of a sterring whell. Draw an arrow from the first priority group, through the second, to the third.
  27. Explain what the arrows indicate.
    If the arrow points clockwise, the asymmetric carbon atom is called R. If it points counterclockwise, it is called S.