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Why is an anti conformation typically more stable than gauche in an acyclic alkane?
Large susbtituents are further apart in anti conformations which minimizes tortional strain
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What are the torsion angles typically associated with eclipsed, anti, and gauche conformations?
- 0 degrees for eclipsed
- 180 degrees for anti
- 60 degrees for gauche
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Which eclipsed conformation should be more strained, C1-C2 in 1,2-diiodoethane or C1-C2 in 1,2-difluoroethane?
The eclipsed conformation in 1,2-diiodoethane should be more strained since I is much bigger than F
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Gauche and anti conformations are both what type of overall conformation?
Both are staggered conformations
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Why is cyclobutane not planar (i.e. flat)?
Being flat would result in significant eclipsing interactions, puckering reduces this
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How many overall conformations are available for cyclohexane?
An infinite number of conformations are possible
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Why are boat conformations typically less stable than chairs?
So-called "flag-pole" interactions destabilize boat conformations
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Why are half-chair conformations less stable than chair conformations?
A half-chair conformation will have significant eclipsing interactions around the ring
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Match the compounds with the appropriate ring-flip equilibrium constant:
t-butylcyclohexane, fluorocyclohexane, isopropylcyclohexane:
K = 32.2, K >9999, K = 1.5
K = 32.2, isopropylcyclohexane
K >9999, t-butylcyclohexane
K = 1.5, fluorocyclohexane
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Which is more stable, cis-1,2-dimethylcyclopropane or trans-1,2-dimethylcyclopropane?
The trans isomer is more stable since it avoids 1,2-torsional strain between the methyl groups
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Which is more stable, cis-1,2-dibromocyclohexane or trans-1,2-dibromocyclohexane?
The trans isomer will be more stable as it can exist in a chair conformation that has no 1,3-diaxial interactions
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Which releases more heat upon combustion, cis-1,2-dimethylcyclopropane or trans-1,2-dimethylcyclopropane?
The cis isomer is less stable so it will release more energy
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Why is the ring-flip equilibrium constant for t-butylcyclohexane so much larger than for methylcyclohexane?
The t-butyl group is very much larger than methyl so the axial possibility is greatly disfavoured
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How many carbons are present in bicyclobutane?
4
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What is wrong with the name bicyclo[0.1.4]heptane?
The numbers are usually arranged in descending order
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Why do substituents larger than H prefer to be equatorial in cyclohexanes?
To avoid destabilizing 1,3-diaxial interactions
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What would the equilibrium constant be for the ring-flip process in cyclohexane itself?
K = 1
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Which should be more stable, cis-1,4-dibromocyclohexane or trans-1,4-dibromocyclohexane?
The trans isomer since both large substituents will be equatorial in the preferred chair conformation
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Why does cyclopropane generate more heat per CH2 group than cyclohexane?
The strain energy within cyclopropane accounts for the extra energy released
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Is the energy difference between reactants and products directly or inversely proportional to the equilibrium constant for that reaction?
Directly proportional (deltaG = -RTlnK)
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