Molecular Conformations and Energy Profiles

The video tutorial covers the drawing and analysis of Newman projections for molecules like ethane, butane, and 2,3-dimethylpentane. It explains the concepts of staggered and eclipsed conformations, torsional strain, and potential energy diagrams. The tutorial also includes practice examples to reinforce understanding of molecular stability and energy barriers.

What is the main reason the staggered conformation of ethane is more stable than the eclipsed conformation?

• It has more hydrogen atoms.

• It has less torsional strain.

• It has a higher energy level.

• It has more carbon atoms.

In the Newman projection of butane, what is the dihedral angle in the anti-conformation?

• 120 degrees

• 60 degrees

• 180 degrees

• 240 degrees

Which conformation of butane is the least stable?

• Gauche conformation

• Eclipsed conformation

• Total eclipse conformation

• Anti-conformation

What is the relationship between potential energy and stability in molecular conformations?

• Higher potential energy means higher stability.

• Lower potential energy means higher stability.

• Potential energy does not affect stability.

• Stability is only affected by the number of atoms.

In 2,3-dimethylpentane, which interaction has more steric strain?

• Hydrogen-hydrogen interaction

• Ethyl-methyl interaction

• Carbon-carbon interaction

• Methyl-methyl interaction

What is the most stable staggered conformation of 2,3-dimethylpentane based on steric interactions?

• One with two ethyl-methyl gauche interactions

• One with one methyl-methyl gauche interaction

• One with no gauche interactions

• One with two methyl-methyl gauche interactions

What is the energy profile of a gauche interaction in 2-methylbutane?

• 4.0 kJ/mol

• 11.0 kJ/mol

• 3.8 kJ/mol

• 6.0 kJ/mol

How much energy is required to rotate butane from its anti-conformation to its totally eclipsed conformation?

• 23 kJ/mol

• 19 kJ/mol

• 15 kJ/mol

• 11 kJ/mol

Which conformation of 2-methylbutane is the most stable?

• Total eclipse conformation

• One with one gauche interaction

• One with two gauche interactions

• Eclipsed conformation

What is the energy value for two methyl groups eclipsing each other?

• 4 kJ/mol

• 6 kJ/mol

• 11 kJ/mol

• 19 kJ/mol