Question

CCC(C)Cl (a) meso-form (b) racemic mixture (c) d-form (d) l-form

Short answer

The molecule is an achiral, symmetrical compound with no chiral centers.

Step-by-step solution

Identify the Chiral Centers

The given molecule, 2-chloro-2-methylpropane ( - CCC(C)Cl -), should be analyzed for chiral centers. A chiral center is a carbon atom that is bonded to four different groups. However, in this molecule, each carbon is either not bonded to four different groups or is not a carbon atom at all. Therefore, there are no chiral centers present.

Determine the Symmetry

Since there are no chiral centers, examine the molecular structure for symmetry. The structure of 2-chloro-2-methylpropane shows that all carbon atoms and their substituents are symmetrically arranged.

Analyze the Possibilities for Optical Isomerism

A meso form typically refers to a system with chiral centers that are symmetric, negating chirality; a racemic mixture consists of equal amounts of left and right-handed enantiomers leading to optical inactivity; d-form and l-form refer to specific optical isomers that rotate plane-polarized light. In the absence of chiral centers, these specific forms cannot exist for this molecule.

Conclude the Type of System

Since the given molecule lacks chiral centers and shows overall symmetry, it cannot be a meso-form, racemic mixture, or exhibit separate d- or l-forms. It is simply an achiral, symmetrical molecule.

Key concepts

Chiral Centers

In organic chemistry, a **chiral center** is a central atom, typically carbon, bonded to four different groups or atoms. This unique arrangement makes the center asymmetric, leading to the existence of optical isomers, also known as enantiomers. Each of these enantiomers is a mirror image of the other, providing distinct properties. The presence of chiral centers is crucial for a molecule to show chirality.

Here is what to remember about chiral centers:

• Chiral centers are often identified by analyzing each carbon atom in a molecule to see if it is bound to four distinct groups.
• A carbon bonded to identical groups or fewer than four distinct groups can't be chiral.
• The absence of chiral centers signifies that a molecule cannot have optical isomers.

The molecule in question, 2-chloro-2-methylpropane, lacks any chiral centers, meaning it cannot exhibit optical isomerism.

Symmetrical Molecules

A **symmetrical molecule** has an even and balanced distribution of substituents and atoms. These molecules display symmetry in their structure, leading to certain predictable physical properties. In the context of chirality, symmetry typically negates the ability for a molecule to have chiral centers or optical activity.

Points to remember about symmetrical molecules:

• They have matched or balanced substituent arrangements around a central core.
• Symmetry often indicates that a molecule is achiral, meaning it does not have chiral centers.
• Symmetrical and achiral molecules do not exhibit meso, racemic, d- or l-forms.

In the example of 2-chloro-2-methylpropane, the molecule's symmetrical nature confirms it lacks chirality and remains non-optically active.

Optical Isomerism

**Optical isomerism** occurs when compounds have the same molecular formula and structure but differ in the orientation of atoms or groups in space, resulting in different interactions with polarized light. This phenomenon arises in molecules with chiral centers and manifests as enantiomers.

Important aspects of optical isomerism include:

• Enantiomers rotate plane-polarized light in opposing directions—one clockwise (d-form), the other counter-clockwise (l-form).
• Meso compounds have multiple chiral centers but still remain achiral due to internal symmetry.
• Racemic mixtures contain equal parts of enantiomers, canceling out optical activity.

In the case of 2-chloro-2-methylpropane, its lack of chiral centers and symmetrical arrangement renders it incapable of forming optical isomers or any related forms.