Newman Projections | Summary and Q&A

TL;DR

Learn about drawing Newman projections of molecules and analyze the relative stability of different conformations.

Key Insights

• ❓ The staggered conformation is generally more stable than the eclipsed conformation due to torsional strain.
• 👥 The anti-conformation of butane, where the methyl groups are farthest apart, is the most stable conformation.
• ❓ The energy barrier to rotation between different conformations represents the energy required to overcome steric strain and convert between them.

Transcript

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Questions & Answers

Q: Why is the staggered conformation more stable than the eclipsed conformation in ethane?

The staggered conformation is more stable due to the torsional strain caused by the eclipsing hydrogen atoms in the eclipsed conformation. This strain leads to higher energy and lower stability.

Q: What is the most stable conformation of butane?

The most stable conformation of butane is the anti-conformation, where the methyl groups are positioned as far apart as possible. This results in the lowest potential energy and highest stability.

Q: What is the dihedral angle between the two methyl groups in the gauche conformation of butane?

The dihedral angle between the two methyl groups in the gauche conformation of butane is 60 degrees. This conformation has two gauche interactions and is less stable than the anti-conformation.

Q: What is the energy barrier to rotation between the total eclipse and anti-conformation of butane?

The energy barrier to rotation between the total eclipse and anti-conformation of butane is 19 kilojoules per mole. This represents the energy required to overcome the steric strain and convert from one conformation to the other.

Summary & Key Takeaways

• Ethane Newman projection: The staggered conformation is more stable than the eclipsed conformation due to torsional strain caused by the eclipsing hydrogen atoms.

• Butane Newman projection: The most stable conformation is the anti-conformation, where the methyl groups are farthest apart, while the least stable is the total eclipse conformation, where the two methyl groups directly eclipse each other.

• Energy barrier: The energy barrier between the total eclipse and anti-conformation of butane is 19 kilojoules per mole.