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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
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Chair-chair interconversion
when two conformations are in equilibrium because they interconvert
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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
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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
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Explain a 1,3-diaxial interaction.
the involvement of substitents on carbon atoms of the ring that bear a 1,3 relationship
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True or False:
1,3-diaxial interactions are present in equatorial conformation.
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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
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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
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The less stable conformation has __ in __.
- both methyl groups
- axial positions
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__ 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
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The most stable conformation of the cis isomer of 1,3-dimethylcyclohexane has the methyl groups as what?
both methyl groups in equatorial positions
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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
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True or Fals:
Cis and trans isomers cannot interconvert and there is no equilibrium between these isomers
true
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In many substituted cyclohexans, the substituents are __.
different sizes
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The energy difference between the axial and equatorial positions for a larger group is __ than for a smaller gorup.
larger
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Ing eneral, if both groups cannot be __, the most stable conformation has the __ adn the __.
- equatorial
- larger group equatorial
- smaller group axial
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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
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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
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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
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fused rings
most common, sharing two adjacent carbon atoms adn the bond between them
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bridged rings
also common, sharing two nonadjacent carbon atoms (the bridgehead carbons) and one or more carbon atoms (the bridge) between them
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Spirocyclic compoudns
in which two rings share only one carbon atom, are relatively rare
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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
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All fused and bdirdged bicyclic systems have __ connecting the __ where the rings connect.
- three bridges
- two bridgehead atoms
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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
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__ is the most common example of a fused ring system.
decalin
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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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