Orgo 7.5-7.7

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  1. Lack of rotation leads to __. Same side: __. Different side: __.
    • cis-trans isomerism (geometric isomerism)
    • cis
    • trans
  2. True or False:
    Not at all alkenes are capable of showing cis-trans isomerism.
  3. If either carbon of the double bond holds two identical groups, it is __.
    not cis trans
  4. __ are unstable unless the ring is large enough (at least eight atoms) to accommodate the __. Therefore, all __ are assumed to be __ unles they are specifically named __. The __ name is rarely used with cycloalkenes, except to distinguish them.
    • trans cycloalkenes
    • trans double bond
    • cycloalkenes
    • cis
    • trans
    • cis
  5. Cis- trans is too __. SO, we use __.
    • ambiguious
    • E-Z system
  6. Steps of E-Z nomenclature:
    • 1) mentally separate the double bonds
    • 2) assign first and second priorities to the two groups
  7. What is E and what is Z?
    • E: two first-priority are on opposite sides
    • Z: two first-priority atoms are together on the same side
  8. Alkenes can be used as __(3)__ and other valuable chemicals.
    • polymers
    • drugs
    • pesticides
  9. A __ is a molecule made up of many __ molecules. An alkene monomer can __ by a chain reaction where additional alkene molecules add to the end of hte growing polymer chain. Becuase these polymers result from addition of many individual alkene units, they are called __. __ are polymers made from monofunctional alkenes such as ethylene and propylene.
    • polymer
    • monomer
    • polymerize
    • addition polymers
    • polyolefins
  10. How can stabilities be compared?

    Alkene energies are often compared by measuring the __: the heat given off during catalytic hydrogenation
    • by converting different compounds to a common product and comparing the heat given off
    • heat of hydrogenation
  11. When an alkene is treated with H in the presence of a __, H adds to the double bond, doing what?

    Hydrogenation is __.

    The difference in stability of cis and trans is the difference in the __.
    • platinum catalyst
    • reducing the alkene to an alkane
    • mildly exothermic
    • heat of hydrogenation
  12. True or Mast: most alkenes with similar substitution patterns give similar heats of hydrogenation.
  13. In practice, we can use __ to compare the stabilities of different alkenes as long as they hydrogenate to give __.
    • heats of hydrogenation
    • alkanes of similar energies
  14. The most stable bonds are those with __. This is called __. In other words, the __ attached to the double-bonded carbons stabilize the alkene.
    • the most alkyl groups attached
    • Zaitsev's rule
    • alkyl groups
  15. Two factors are probably responsible for hte stabilizing effect of alkyl groups on a double bond. 
    What is the first?
    alkyl groups are electron-donating, and they contribute electron density to the pi bond. 
  16. Two factors are probably responsible for hte stabilizing effect of alkyl groups on a double bond. 
    What is the second?
    bulky substituents like alkyl groups are best situated as far apart as possible.
  17. In an alkane, the bulky substitutensts are separated by the __. A double bond increases this separation to about __.
    • tetrahedral bond angle, about 109.5
    • 120
  18. In general, __ are separated best by the most highly substituted double bond. This steric effect is illustrated for two __ (isomers that differ only in the position of the double bond). The isomer with the monosubbed double bond separates the alkyl groups by only __, while the trisubbed double bond separates them by about __.
    • alkyl groups
    • double-bond isomers
    • 109.5
    • 120
  19. What do heats of hydrohalogenation show? Why is this reasonable?
    • trans are most stable than cis
    • alkyl substituents are separaetd farther in trans than they are in cis
  20. Most cycloalkenes react like __. The presence of a ring makes a major difference only if there is __, either because of a small ring or because of a trans double bond. rings that are __ or larger can easily accommodate double bonds, and these cycloalkenes react much like straight- chain alkenes. __ and __ show evidence of ring strain, however.
    • acyclic (noncyclic) alkenes
    • ring strain
    • 5-membered 
    • 3 and 4-membered rings
  21. Which has a higher heat of dehydrogenation: cyclobutene or cyclopentene
    • cyclobutene
    • extra ting strain by virtue of the small ring
  22. Another difference between cyclic and acyclic alkenes is the relatinship between __ and __. In acyclic alkenes, the __ are usually more stable; but the __ of small cycloalkenes are rare, and those with fewer than 8 are usually unstable at room temp.
    • cis and trans isomers
    • trans
    • trans isomers
  23. What is the problem with making a trans cycloalkene?
    lies in the geometry of the trans double bond; the alkyl groups are so far apart that several carbon atoms are needed to complete the ring
  24. Cyclohexene is too strained to be isolated, but __ can be isolated at low temps. __ is stable at room temp, although its cis isomer is still more stable.
    • trans-cyclohexene 
    • trans cyclooctene
  25. Bredt's Rule
    a bridged bicyclic compound cannot have a double at a bridgehead position unless one of the rings contains at least eight carbon atoms
  26. bicyclic
    bridged carbon atoms
    bridged bicylic
    • one that contains two rings
    • part of both rings, with three links connecting them
    • at least one C atom is in each of the three links between teh bridgehead carbons
  27. If there is a double bond at the bridgehead carbon of a bridged bicyclic system, then what?
    one of the two rings contains a cis double bond adn the other must contain a trans double bond
  28. If the larger ring contains a t least eight carbon atoms, then what?
    it can contain a trans double bond and the bridgehead double bond is stable
  29. In general, compounds that violate Bredt's rule are __.
    not stable at room temp
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Orgo 7.5-7.7
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