36 Questions
What is the type of conformation shown when staring down the carbon two-three bond in the butane molecule?
Staggered conformation
What happens when the front carbon is rotated 60 degrees while keeping the back carbon stationary?
The molecule changes to an eclipsed conformation
What is the term used to describe the phenomenon where the hydrogens are close enough to hit in the model set?
Steric hindrance
What is the result of rotating the butane molecule 60 degrees from the staggered conformation?
An eclipsed conformation
What is the purpose of the energy diagram shown in the video?
To compare the potential energy of different conformations
What is the initial conformation of the butane molecule in the video?
Staggered conformation
What happens when the butane molecule is rotated 60 degrees from the eclipsed conformation?
The molecule changes to a staggered conformation
What is the relationship between the hydrogens in the eclipsed conformation of the butane molecule?
They are close enough to hit
What is the energy cost associated with a pair of eclipsed hydrogens?
4 kilojoules per mole
What is the energy cost associated with a methyl group eclipsing a hydrogen?
6 kilojoules per mole
In the anti-conformation, what is the arrangement of the bonds?
Staggered
What is the energy cost associated with two methyl groups eclipsing each other?
11 kilojoules per mole
What type of strain is present when two methyl groups eclipse each other?
Steric strain
Why is the eclipsed conformation higher in potential energy?
Because of the steric hindrance
What is the total energy cost of the highest-energy eclipsed conformation?
19 kilojoules per mole
What happens when the two methyl groups are close together in the eclipsed conformation?
They become less stable
Why is the anti-conformation the most stable?
Because the bonds are staggered
What is the energy difference between the anti-conformation and the eclipsed conformation?
16 kilojoules per mole
What is the energy difference between the staggered and eclipsed conformations?
16 kilojoules per mole
What is the energy difference between the two staggered conformations?
3.8 kilojoules per mole
Which conformation is less stable?
Eclipsed conformation
What is the dihedral angle between the two methyl groups in the anti conformation?
180 degrees
What is the name of the conformation with the highest potential energy?
Eclipsed conformation
What is the energy difference between the two eclipsed conformations?
3 kilojoules per mole
What is the name of the conformation with the lowest potential energy?
Staggered conformation
What is the energy difference between the staggered and eclipsed conformations when rotating 60 degrees?
3.8 kilojoules per mole
Which of the following conformations are degenerate?
Two eclipsed conformations
What is the name of the conformation with a dihedral angle of 180 degrees?
Anti conformation
What is the primary reason why the gauche conformation has a higher potential energy than the anti-conformation?
Steric hindrance
Which conformation has the highest potential energy?
Eclipsed conformation with methyl groups close together
What is the angle between the methyl groups in the gauche conformation?
60 degrees
Why is the eclipsed conformation with methyl groups close together higher in energy than the eclipsed conformation?
Due to electrostatic repulsion between the methyl groups
Which of the following conformations is the most stable?
Anti-conformation
What is the main effect of the hydrogens on the methyl groups in the gauche conformation?
Destabilizing effect
What is the primary factor contributing to the higher potential energy of the gauche conformation compared to the anti-conformation?
Steric hindrance
Why do the hydrogens on the methyl groups in the gauche conformation get close to each other?
Due to the dihedral angle
Study Notes
Conformations of Butane
- Butane has different conformations, which can be identified by rotating the molecule.
- The staggered conformation of butane is more stable than the eclipsed conformation.
- In a staggered conformation, bonds are staggered, and in an eclipsed conformation, bonds are eclipsed.
- Steric hindrance, or steric strain, occurs when hydrogens or methyl groups are close enough to touch, which is destabilizing.
- From the eclipsed conformation, rotating 60 degrees results in a staggered conformation.
- The energy difference between the staggered and eclipsed conformations is approximately 16 kilojoules per mole.
Energy Diagram
- The energy diagram shows the different conformations of butane and their corresponding energies.
- The staggered conformation has a lower energy than the eclipsed conformation.
- The energy difference between the two staggered conformations is approximately 3.8 kilojoules per mole.
- The energy difference between the two eclipsed conformations is approximately 3 kilojoules per mole.
Newman Projection
- A Newman projection is used to represent the molecule in a 2D plane.
- Carbon number three is represented by a circle in the Newman projection.
- The dihedral angle between the two methyl groups is 180 degrees in the anti conformation.
Conformations in Detail
- The anti conformation is the most stable conformation of butane.
- In the anti conformation, the dihedral angle is 180 degrees, and the methyl groups are as far apart as possible.
- Rotating 60 degrees from the anti conformation results in an eclipsed conformation.
- The eclipsed conformation has an energy cost of 16 kilojoules per mole due to eclipsed hydrogens and methyl groups.
- The highest-energy conformation is the eclipsed conformation with two methyl groups eclipsing each other, which has an energy cost of 19 kilojoules per mole.
- The gauche conformation has a dihedral angle of 60 degrees and is higher in energy than the anti conformation due to steric hindrance.
Energy Costs
- The energy cost of a pair of eclipsed hydrogens is approximately 4 kilojoules per mole.
- The energy cost of a methyl group eclipsing a hydrogen is approximately 6 kilojoules per mole.
- The energy cost of two methyl groups eclipsing each other is approximately 11 kilojoules per mole.
This quiz explores the conformations of the butane molecule, specifically the staggered and eclipse conformations that occur when rotating the carbon bonds.
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