Question

Which of the following is not a conformation of cyclohexane?

Short answer

The correct answer depends on the specific options provided in the question, which are not stated here. To find the answer, examine each option and compare it to the valid conformations of cyclohexane: chair, boat, and twist-boat. The option that does not match any of these conformations is the one that is not a valid conformation of cyclohexane.

Step-by-step solution

Understand the conformations of cyclohexane

Cyclohexane can exist in three primary conformations due to its three-dimensional structure. These conformations include the chair conformation, which looks like a chair; the boat conformation, shaped like a boat; and the twist-boat conformation, a distorted version of the boat conformation which reduces torsional strain. The chair conformation is the most stable due to the carbon atoms being as far apart as possible minimizing electron repulsion.

Examine each option

Each option A, B, C, and D should be examined and compared to the valid conformations.

Identify the invalid conformation

The option which does not match the chair, boat, or twist-boat conformations is the one that is not a valid conformation of cyclohexane. This will depend on the specific options given in the question. Note: This response is dependent on the specific options provided in the question which are not provided in this case. We are unable to directly provide the correct answer without having these options present.

Key concepts

Chair Conformation

In the fascinating world of cyclohexane conformations, the chair conformation stands out as the most stable. It resembles the profile of a chair, where the carbons are arranged to minimize electron repulsion among themselves. This stability arises because in the chair conformation, all the carbon-hydrogen bonds are staggered. This ensures minimal torsional strain.

• The carbon atoms are positioned such that each is as far away from the others as possible. This minimizes the steric hindrance.
• A characteristic feature of the chair conformation is that it alternates atoms above and below the plane along the ring.

This stability makes the chair conformation a preferred structure for cyclohexane. Inner forces push the structure to remain in this shape. Because of this, the chair conformation is widely studied and used as a reference.

Boat Conformation

The boat conformation is another possible shape for cyclohexane, though less stable than the chair conformation. Imagine a small boat floating on the water—that's where this conformation gets its name. In the boat conformation, all carbons are in a single plane, suggesting none are axial or equatorial, though higher energy is stored due to eclipsed interactions.

• This shape sees significant torsional strain because of the eclipsing hydrogen atoms across the ring.
• There exist steric interactions known as 'flagpole interactions' between hydrogen atoms (or substituents) at the bow and stern, leading to instability.

These interactions contribute to the less frequent natural occurrence of the boat conformation in cyclohexane molecules compared to the chair. The configuration is mostly found in transient states as molecules transition between conformations.

Twist-Boat Conformation

The twist-boat conformation is a slight variation from the boat conformation. Imagine gently twisting a piece of paper to alleviate pressure at certain points. By shifting a couple of carbon atoms slightly out of the plane, torsional strain in the twist-boat conformation is reduced compared to the regular boat conformation.

• This structure still involves more energy than the chair conformation, yet it is slightly more stable than the simple boat due to fewer hydrogen eclipses.
• The twist helps relieve flagpole interactions seen in the boat configuration.

The twist-boat conformation represents a compromise between the strain of the boat form and the full stability of the chair form. It's like finding a comfortable balance when perching between opposing forces. Although rare and short-lived, this twist in the boat configuration illustrates the dynamic nature of cyclohexane conformations.