Question

Which one of the following conformations of cyclohexane is chiral? (a) Rigid (b) Chair (c) Boat (d) Twist boat

Short answer

The twist boat conformation of cyclohexane is chiral.

Step-by-step solution

Understand the Structure of Cyclohexane

Cyclohexane is a six-carbon ring that can adopt several conformations to relieve angle strain and steric hindrance. The most common conformations include the chair, boat, and twist boat.

Definition of Chirality

Chirality refers to a molecule that is not superimposable on its mirror image. In cyclohexane, chirality can occur if the conformation lacks a plane or center of symmetry.

Analyze the Chair Conformation

The chair conformation of cyclohexane is completely symmetrical with all bond angles at 109.5°, making it achiral because it has a plane of symmetry.

Analyze the Boat Conformation

The boat conformation also has a plane of symmetry. Despite having carbons that are equivalent, it is achiral due to this symmetry plane.

Analyze the Twist Boat Conformation

The twist boat conformation lacks a plane of symmetry and thus can be chiral. It relieves some steric strain present in the regular boat conformation, but this lack of symmetry leads to chirality.

Key concepts

Chirality in cyclohexane

Chirality can often be a challenging but fascinating topic in chemistry. When we talk about chirality in cyclohexane, we refer to whether its three-dimensional structure can be non-superimposable on its mirror image.
In simple terms, if you cannot place the molecule on top of its mirror image to make it exactly overlap, it is considered chiral.
For chirality to occur in cyclohexane, the conformation must lack a plane or center of symmetry. This uniqueness makes studying chirality exciting as it plays a critical role in how molecules behave and interact.

Chair conformation

The chair conformation is the most stable and common form of cyclohexane. This is because it minimizes steric strain, allowing the ring's carbon atoms to adopt the most staggered and energetically favorable position.

• All carbon-carbon bond angles are close to 109.5°
• No torsional strain exists, making the molecule stable

However, the chair conformation is achiral. It has a plane of symmetry where one half of the molecule can be reflected to match the other half perfectly. This symmetry is why the chair structure does not have chirality properties in cyclohexane.

Boat conformation

The boat conformation of cyclohexane creates a different shape where some steric strain is introduced due to eclipsing interactions between hydrogen atoms. In this conformation, the molecule takes the shape of a boat with both ends bent upwards.

• Increased steric strain compared to the chair conformation
• The molecule still retains a plane of symmetry

Despite having a symmetrical feature, this configuration remains achiral due to the symmetry plane that allows the molecule to be superimposed onto its mirror image.

Twist boat conformation

The twist boat conformation of cyclohexane introduces a unique perspective because, unlike the plane of symmetry seen in other conformations, it twists to reduce some of the steric strain present in the boat form.

• This twisting eliminates the plane of symmetry
• It results in less torsional strain than the boat conformation

Without a plane of symmetry, the twist boat conformation can be chiral if the molecule remains non-superimposable on its mirror image. This characteristic makes the twist boat conformation an interesting aspect of studying chirality in cyclohexane.