Orgo txt. 2.5-2.8

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Orgo txt. 2.5-2.8
2013-09-04 23:30:24
CHM 201

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  1. Dashed lines indicate __? Wedges indicate __?
    • bonds that go backward, away from teh reader
    • forward, toward the reader
  2. What is rule one?
    both sigma bonding electrons and lone pairs can occupy hybrid orbitals. The number of hybrid orbitals on an atom is computed by adding the number of sigma bonds and the number of lone pairs of electrons on that atom
  3. Because the first bond to another atom is always a __, the number of hybrid orbitals may be computed by adding the number of __ to the number of atoms bonded to the __.
    • sigma bond
    • lone pairs
    • central atom
  4. What is rule two?
    use the hybridization and geometry that give the widest possible separation of the calculated number of bonds and lone pairs
  5. hybridization, geometry and bond angle
    • sp
    • linear
    • 180
  6. hybridization, geometry and bond angle
    • sp2
    • trigonal
    • 120
  7. hybridization, geometry and bond angle
    • tetrahedral
    • 109.5
    • sp3
  8. The numbe rof hybrid orbitals obtained equals __. __ take up more space than __; thus, they compress the __.
    • the number of atomic orbitals combined
    • lone pairs of electrons
    • bonding pairs of electrons 
    • bond angles
  9. Rule three
    if two or three pairs of electrons form a multiple bond between two atoms, the first bond is a sigma bond formed by a hybrid orbital. The second is a pi bond, consisting of two lobes above and below the sigma bond, formed by two unhybridized p orbitals. The third bond of a triple bond is another pi bond, perpendicular to the first pi bond
  10. True or False:
    All bonds are hard to rotate.
    • False
    • SOme bonds rotate easily, but others do not
  11. What happens if a bond rotates easily?
    each moleucle can rotate through the different angular arrangements of atoms.
  12. What happens if a bond cannot rotate?
    different angular arrangements may be distinct compounds (isomers) with different properties
  13. Structures differing in only rotations about a single bond are called __.
  14. What are the two types of bonds that can exist in conformations(think ethane for example)?
    • parallel (eclipsed)
    • staggered
  15. Generalize rotation with bonding.
    Rotation about single bonds is allowed, but double bonds are rigid and cannot be twisted.
  16. Because double bonds are rigid, what can we do?
    separate and isolate compounds that differ only in how their substituents are arranged on a double bond
  17. When we separate compounds arranged around a double bond, the molecule with the groups on the same side of the double bond are __; opposite side are __.
    • cis 
    • trans
  18. __ are different compounds with the same molecular formula.
  19. __ are isomers that differ in their bonding sequence; that is, their atoms are connected differently.
    constitutional isomers (structural isomers)
  20. Two compounds can be isomers because tehy are different __ with different __ but have the same __
    • compounds
    • properties
    • molecular formula
  21. True or False: the number of isomers decreases as the number of carbon atoms increases.
    • True or False: the number of isomers decreases as the number of carbon atoms increases.
    • increases
  22. Besides branching, how else may constitutional isomers differ?
    in the position of a double bod or other group or by having a ring or some other feature
  23. __ are isomers that differ only in how their atoms are oriented in space. Their atoms are bonded in the same order, however.
    • Stereoisomers
    • (think cis and trans)
  24. __ are the only type of stereoisomerism. The study of the structure and chem of stereoisomers is called __.
    • cis and trans isomers
    • stereochemistry
  25. __ are also called __ because they differ in the geometry of the groups on a __ The __ is always the one with similar groups on the same side of hte double bond, and the __ has similar groups on opposite sides of the double bond.
    • cis-trans isomers
    • geometric isomers
    • cis isomer
    • trans isomer
  26. To have cis-trans isomerism, what?
    Reversint the positions (does/ does not) give a different compound.
    • there must be two different groups on each end of hte double bond
    • does not

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