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Level 184

Conformations of Cycloalkanes

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Why is there torsional strain in cyclopropane?
Because the molecule is planer all the hydrogen sulfide are in the eclipsed conformation.
Why is there angle strain in cyclopropane?
Because the molecule is shaped like an equilateral triangle which has 60 degree angles while the ideal bond angle is 109.5 degrees.
It has banana bonds
What does the cyclopropane molecule have in order to avoid its angle strain being too high?
What is the cost of having banana bonds
Losing bond strength. Banana bonds are considerably weaker than normal C-C bonds.
a family of organic compounds whose functional group is a carbon-carbon double bond
Cyclopropane has similar reactivity to alkenes because
Cyclopropane a banana bonds have the same energy has a pi bond which are found in Allene's' double bonds.
Why are banana bonds weaker?
Because the orbital overlap is not as good.
Why is cyclopropane very reactive?
Because opening the ring relieves both torsional and angle strain
To minimize torsional strain.
Why does cyclobutane adopt a puckered conformation?
Cyclobutane has what kind of strains?
Small torsional strain and considerable angle strain.
Carbons in an eclipsed conformation.
Torsional strain is caused by having
Steric strain is caused by having
Substituents crash into each other. This happens when the molecule takes on an eclipsed conformation (has both torsional and steric strain) or a gauche conformation (only steric strain).
Gauche conformation happens when
Only the substitute to are crashing into one another causing only steric strain.
What is the cost of cyclobutane's puckered conformation?
Increased angle strain. Angle goes from 90 degrees to 88 degrees.
Envelope and half chair.
What are the preferred conformations of cyclopentane?
Some torsional strain
What kind of strain does cyclopentane have?
What does the envelope position look like?
Only one carbon is up, the four others are on the same plane.
What does the half chair position look like?
One carbon is up and one is down, the 3 others are on the same plane.
Chair conformation
Most stable conformation of cyclohexane
Boat conformation
Which conformation of cyclohexane has the most strain?
Why doesn't the boat conformation not really a conformation, and instead a transition state?
The boat conformation is the maximum energy on an energy diagram and the maximum energy on energy diagrams are transition states.
Transition states are
Maximums on energy, where a molecule just passes through but does not spend any time in
Twist-boat conformation has what kinds of strain?
For practical purposes only torsional strain. Because the twisting of the ring does not remove all of the torsional strain.
The same energy
2 alternate chair formations have
Which substituents are more stable axial or equatorial?
Equatorial, the more equatorial substituents you have relative to axial substitute to the more stable the conformation.
Why are axial substituents unstable?
Because they have steric interactions with the axial hydrogenated on the same side of the ring.
1,3-diaxial interactions
Steric interactions between axial substituents and axial hydrogen sulfide on the same side of the ring is called