Which conformation in each of the following pairs has the least strain energy?
(a)

Verified step by step guidance

Step 1: Analyze the two conformations provided in the image. The first conformation is a planar structure, while the second conformation is a chair conformation of cyclohexane.

Step 2: Recall that strain energy in cyclohexane arises from factors such as torsional strain (from eclipsing interactions) and steric strain (from crowding of substituents). The chair conformation minimizes these strains.

Step 3: Understand that the planar conformation has significant torsional strain due to eclipsing interactions between adjacent hydrogen atoms. Additionally, steric strain may arise from the proximity of substituents.

Step 4: The chair conformation of cyclohexane is the most stable conformation because it eliminates torsional strain by staggering all bonds and minimizes steric strain by placing substituents in equatorial positions when possible.

Step 5: Conclude that the chair conformation has the least strain energy compared to the planar conformation, making it the more stable structure.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Conformational Analysis

Conformational analysis involves studying the different spatial arrangements of atoms in a molecule that can be interconverted by rotation around single bonds. This analysis helps in understanding the stability of various conformations, as some arrangements may lead to steric hindrance or torsional strain, affecting the overall energy of the molecule.

Strain Energy

Strain energy refers to the energy stored in a molecule due to the distortion of its normal bond angles and lengths. In organic molecules, factors such as steric strain (from repulsion between atoms) and torsional strain (from eclipsing interactions) contribute to the overall strain energy, influencing the stability and reactivity of different conformations.

Stability of Conformations

The stability of conformations is determined by the balance of various types of strain energy present in a molecule. Generally, conformations that minimize steric and torsional strain are more stable and have lower energy. Understanding which conformation has the least strain energy is crucial for predicting the preferred structure of a molecule in a given context.

Which conformation in each of the following pairs has the least strain energy?(a)