Rotational Energy Barrier in 2, 3-Dimethylbutane

In order to determine the rotational energy barrier between the most stable and least stable conformations of 2, 3-dimethylbutane, we need to consider the energy contributions from different interactions along the C2C3 bond. The given energies (kcal mol1) for H/CH3 eclipsing, CH3/CH3 eclipsing, and CH3/CH3 gauche are 1.8, 2.9, and 0.9, respectively.

Understanding Conformational Analysis
Conformational analysis involves the study of different conformations of a molecule by rotating around its single bonds. In the case of 2, 3-dimethylbutane, the molecule can adopt different conformations by rotating around the C2C3 bond, resulting in different spatial arrangements of the methyl groups.

Most Stable Conformation
The most stable conformation of 2, 3-dimethylbutane is the one with minimum steric hindrance and maximum stability. In this conformation, the methyl groups are in the anti or gauche positions, which minimizes steric interactions between them.

Least Stable Conformation
The least stable conformation of 2, 3-dimethylbutane is the one with maximum steric hindrance and minimum stability. In this conformation, the methyl groups are in the eclipsed position, resulting in strong steric interactions between them.

Calculating the Rotational Energy Barrier
To calculate the rotational energy barrier, we need to consider the energy difference between the most stable and least stable conformations. This energy difference is determined by the energy contributions from H/CH3 eclipsing, CH3/CH3 eclipsing, and CH3/CH3 gauche interactions.

Energy Contributions:
- H/CH3 Eclipsing: 1.8 kcal mol1
- CH3/CH3 Eclipsing: 2.9 kcal mol1
- CH3/CH3 Gauche: 0.9 kcal mol1

Calculating the Energy Difference:
The energy difference between the most stable and least stable conformations is given by the sum of energy contributions from H/CH3 eclipsing and CH3/CH3 eclipsing interactions.

Energy Difference = H/CH3 Eclipsing + CH3/CH3 Eclipsing
Energy Difference = 1.8 kcal mol1 + 2.9 kcal mol1
Energy Difference = 4.7 kcal mol1

Conclusion:
The rotational energy barrier between the most stable and least stable conformations of 2, 3-dimethylbutane along the C2C3 bond is 4.7 kcal mol1. However, the correct answer is given as '1' kcal mol1. It is possible that there is an error in the given energies or there is some additional information or assumptions not provided in the question. Without further information, it is not possible to explain how the correct answer is '1' kcal mol1.