Podcast
Questions and Answers
What is the type of conformation shown when staring down the carbon two-three bond in the butane molecule?
What is the type of conformation shown when staring down the carbon two-three bond in the butane molecule?
- Staggered conformation (correct)
- Rotational conformation
- Steric hindrance conformation
- Eclipsed conformation
What happens when the front carbon is rotated 60 degrees while keeping the back carbon stationary?
What happens when the front carbon is rotated 60 degrees while keeping the back carbon stationary?
- The molecule breaks apart
- The molecule remains in a staggered conformation
- The molecule changes to an eclipsed conformation (correct)
- The molecule experiences steric hindrance
What is the term used to describe the phenomenon where the hydrogens are close enough to hit in the model set?
What is the term used to describe the phenomenon where the hydrogens are close enough to hit in the model set?
- Steric hindrance (correct)
- Rotational strain
- Eclipsed conformation
- Staggered conformation
What is the result of rotating the butane molecule 60 degrees from the staggered conformation?
What is the result of rotating the butane molecule 60 degrees from the staggered conformation?
What is the purpose of the energy diagram shown in the video?
What is the purpose of the energy diagram shown in the video?
What is the initial conformation of the butane molecule in the video?
What is the initial conformation of the butane molecule in the video?
What happens when the butane molecule is rotated 60 degrees from the eclipsed conformation?
What happens when the butane molecule is rotated 60 degrees from the eclipsed conformation?
What is the relationship between the hydrogens in the eclipsed conformation of the butane molecule?
What is the relationship between the hydrogens in the eclipsed conformation of the butane molecule?
What is the energy cost associated with a pair of eclipsed hydrogens?
What is the energy cost associated with a pair of eclipsed hydrogens?
What is the energy cost associated with a methyl group eclipsing a hydrogen?
What is the energy cost associated with a methyl group eclipsing a hydrogen?
In the anti-conformation, what is the arrangement of the bonds?
In the anti-conformation, what is the arrangement of the bonds?
What is the energy cost associated with two methyl groups eclipsing each other?
What is the energy cost associated with two methyl groups eclipsing each other?
What type of strain is present when two methyl groups eclipse each other?
What type of strain is present when two methyl groups eclipse each other?
Why is the eclipsed conformation higher in potential energy?
Why is the eclipsed conformation higher in potential energy?
What is the total energy cost of the highest-energy eclipsed conformation?
What is the total energy cost of the highest-energy eclipsed conformation?
What happens when the two methyl groups are close together in the eclipsed conformation?
What happens when the two methyl groups are close together in the eclipsed conformation?
Why is the anti-conformation the most stable?
Why is the anti-conformation the most stable?
What is the energy difference between the anti-conformation and the eclipsed conformation?
What is the energy difference between the anti-conformation and the eclipsed conformation?
What is the energy difference between the staggered and eclipsed conformations?
What is the energy difference between the staggered and eclipsed conformations?
What is the energy difference between the two staggered conformations?
What is the energy difference between the two staggered conformations?
Which conformation is less stable?
Which conformation is less stable?
What is the dihedral angle between the two methyl groups in the anti conformation?
What is the dihedral angle between the two methyl groups in the anti conformation?
What is the name of the conformation with the highest potential energy?
What is the name of the conformation with the highest potential energy?
What is the energy difference between the two eclipsed conformations?
What is the energy difference between the two eclipsed conformations?
What is the name of the conformation with the lowest potential energy?
What is the name of the conformation with the lowest potential energy?
What is the energy difference between the staggered and eclipsed conformations when rotating 60 degrees?
What is the energy difference between the staggered and eclipsed conformations when rotating 60 degrees?
Which of the following conformations are degenerate?
Which of the following conformations are degenerate?
What is the name of the conformation with a dihedral angle of 180 degrees?
What is the name of the conformation with a dihedral angle of 180 degrees?
What is the primary reason why the gauche conformation has a higher potential energy than the anti-conformation?
What is the primary reason why the gauche conformation has a higher potential energy than the anti-conformation?
Which conformation has the highest potential energy?
Which conformation has the highest potential energy?
What is the angle between the methyl groups in the gauche conformation?
What is the angle between the methyl groups in the gauche conformation?
Why is the eclipsed conformation with methyl groups close together higher in energy than the eclipsed conformation?
Why is the eclipsed conformation with methyl groups close together higher in energy than the eclipsed conformation?
Which of the following conformations is the most stable?
Which of the following conformations is the most stable?
What is the main effect of the hydrogens on the methyl groups in the gauche conformation?
What is the main effect of the hydrogens on the methyl groups in the gauche conformation?
What is the primary factor contributing to the higher potential energy of the gauche conformation compared to the anti-conformation?
What is the primary factor contributing to the higher potential energy of the gauche conformation compared to the anti-conformation?
Why do the hydrogens on the methyl groups in the gauche conformation get close to each other?
Why do the hydrogens on the methyl groups in the gauche conformation get close to each other?
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.
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Description
This quiz explores the conformations of the butane molecule, specifically the staggered and eclipse conformations that occur when rotating the carbon bonds.
