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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
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
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
Gauche and anti conformations are both what type of overall conformation?
Both are staggered conformations
Why is cyclobutane not planar (i.e. flat)?
Being flat would result in significant eclipsing interactions, puckering reduces this
How many overall conformations are available for cyclohexane?
An infinite number of conformations are possible
Why are boat conformations typically less stable than chairs?
So-called "flag-pole" interactions destabilize boat conformations
Why are half-chair conformations less stable than chair conformations?
A half-chair conformation will have significant eclipsing interactions around the ring
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
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
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
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
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
How many carbons are present in bicyclobutane?
What is wrong with the name bicyclo[0.1.4]heptane?
The numbers are usually arranged in descending order
Why do substituents larger than H prefer to be equatorial in cyclohexanes?
To avoid destabilizing 1,3-diaxial interactions
What would the equilibrium constant be for the ring-flip process in cyclohexane itself?
K = 1
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
Why does cyclopropane generate more heat per CH2 group than cyclohexane?
The strain energy within cyclopropane accounts for the extra energy released
Is the energy difference between reactants and products directly or inversely proportional to the equilibrium constant for that reaction?
Directly proportional (deltaG = -RTlnK)