Orgo Ch 3.14-

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DesLee26
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Orgo Ch 3.14-
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2013-09-26 22:47:03
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CHM 201
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  1. A substituent on a __ can occupy either an __ or an __ position. In many cases, the reactivity of the substituent depends on whetehr its position is __ or __.
    • cyclohexane ring (in the chair conformation)
    • axial or an equatorial position
    • axial or equatorial
  2. Chair-chair interconversion
    when two conformations are in equilibrium because they interconvert
  3. The chair with a methyl group in an __ is the msot stable conformation, about 7.6 kJ/ mol lower in energy than the conformation with the methyl group on the __.

    However, both of these chair conformations are lower in energy than any __.
    • equatorial position
    • axial
    • boat conformation
  4. The axial methylcyclohexane has two __, each representing about 3.8 kJ of additional eergy.
    The __ has no __. Therefore, we predict that the __ is higher in energy by 7.6 kJ per mole.
    • gauche interactions
    • equatorial methyl group
    • gauche interactions
    • axial conformation
  5. Explain a 1,3-diaxial interaction.
    the involvement of substitents on carbon atoms of the ring that bear a 1,3 relationship
  6. True or False: 
    1,3-diaxial interactions are present in equatorial conformation.
    • False
    • not present
  7. A larger group usually has a __ between the __ and __ becuase the __ is stronger for larger groups.
    • larger energy difference
    • axial equatorial positions
    • 1,3-diaxial interaction
  8. The __ between substituents in __ is particularly severe when there are __ on two carbon atoms that bear a __, as in the __ of __ shown in the text.
    • steric interference
    • axial positions
    • large groups
    • 1,3-diaxial relationship
    • two chair conformations of cis 1,3-dimethylcyclohexane
  9. The less stable conformation has __ in __.
    • both methyl groups 
    • axial positions
  10. __ does not have a conformation with a __ between two __ groups. Either of its __ palces one __ in an __ and one in an __. These conformations have __, and they are present in equal amounts
    • trans-1,30dimethylcyclohexane
    • 1,3-diaxial interactin
    • methyl
    • chair conformations
    • methyl gorup
    • axial position
    • equatorial position
    • equal energies
  11. The most stable conformation of the cis isomer of 1,3-dimethylcyclohexane has the methyl groups as what?
    both methyl groups in equatorial positions
  12. Either conformation fo the rans isomer of 1,3-dimethylcyclohexane places the methyl groups? 
    What does this mean?
    • one methyl group in an axial position
    • trans isomer is higher in ergery than the cis isomer by about 7.6 kJ/ mol, the energy differece between axial and equatorial methyl groups
  13. True or Fals:
    Cis and trans isomers cannot interconvert and there is no equilibrium between these isomers
    true
  14. In many substituted cyclohexans, the substituents are __.
    different sizes
  15. The energy difference between the axial and equatorial positions for a larger group is __ than for a smaller gorup.
    larger
  16. Ing eneral, if both groups cannot be __, the most stable conformation has the __ adn the __.
    • equatorial
    • larger group equatorial
    • smaller group axial
  17. Some groups, sucha s tertiary-butyl groups, are so bulky that they are extremely __ in __ positions. Regardless of the other gorups present, cyclohexanes with tert-butyl substituents are most stable when what?
    • strained
    • axial positions
    • the tert-butyl group is in an equatorial position
  18. If two tert-butyl groups are attached to the ring, both of them are much less strained in__. When neither __ allows both bulky groups to be __, they may force the ring into a __.
    • equatorial positions
    • chair conformation
    • equatorial
    • twist boat conformation
  19. Two or more rings can be joined into __ or __ systems. There are three ways that two rings may be joined: name them
    • bicyclic 
    • polycyclic
    • fused rings
    • bridged rings
    • spirocyclic compounds
  20. fused rings
    most common, sharing two adjacent carbon atoms adn the bond between them
  21. bridged rings
    also common, sharing two nonadjacent carbon atoms   (the bridgehead carbons) and one or more carbon atoms (the bridge) between them
  22. Spirocyclic compoudns
    in which two rings share only one carbon atom, are relatively rare
  23. The name of a bicyclic compound is based on the name of the __
    alkane having the sme number of carbons as there are int he ring system following the prefix bicyclo and a set of brackets enclosing three numbers
  24. All fused and bdirdged bicyclic systems have __ connecting the __ where the rings connect.
    • three bridges
    • two bridgehead atoms
  25. The bumers in the brackets give what
    the numer of carbon atoms in each of the three bridges conneting the bridgehead carbons, in order of decreasing size
  26. __ is the most common example of a fused ring system.
    decalin
  27. The conformation of cis-decalin is somehwat __,but the trans-isomer is quite __. If one of the rings in the trans isomer did a __, the bonds to the second ring would both become __ and would be directed __ aprt. This is an impssible conformation and it prevents any __ in __.
    • flexible
    • rigid
    • chair-chair interconversion
    • axial
    • 180 degrees
    • chair-chair interconversion
    • trans-decalin

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