Question

arrange the following newman projections of butane in order of energy.
i < iii < ii < iv
iii < i < iv < ii
ii < iv < i < iii
iv < ii < iii < i

Explanation:

Step1: Identify conformation types

The energy of butane conformations depends on steric hindrance. Gauche and eclipsed conformations have higher energy due to repulsions. Anti - conformation has the lowest energy.

Step2: Analyze each projection

• Projection III is the anti - conformation (lowest energy) with the two methyl groups as far apart as possible.
• Projection I is a gauche conformation with some steric repulsion between the methyl groups.
• Projection IV is a partially eclipsed conformation with methyl - hydrogen and hydrogen - hydrogen eclipsing interactions.
• Projection II is a fully eclipsed conformation (highest energy) with methyl - methyl eclipsing interaction.

Step3: Arrange in energy order

Based on the above analysis, the order of increasing energy is III < I < IV < II.

Answer:

III<I<IV<II