Problem 59 - Chemistry: The Central Science

Question

Which of the following objects is chiral? (a) a left shoe, (b) a slice of bread, (c) a wood screw, (d) a molecular model of \(\mathrm{Zn}(\mathrm{en}) \mathrm{Cl}_{2}\), (e) a typical golf club.

Step-by-Step Solution

Answer

The chiral objects among the given options are: (a) a left shoe, (c) a wood screw, (d) a molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\), and (e) a typical golf club.

Step 1: Analyze Each Object

Let's analyze each object one by one and determine whether it is chiral or not. (a) A left shoe: A left shoe is not symmetric and will have a non-superposable mirror image (a right shoe). So, a left shoe is chiral. (b) A slice of bread: A slice of bread has approximate mirror symmetry when viewed from the front side. Therefore, it's not chiral. (c) A wood screw: A wood screw has one side that spirals upwards, which will not align with its mirror image, making it chiral. (d) A molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\): The molecule has a central zinc atom bonded to two chlorine atoms and two ethylenediamine ligands. The ligands create an asymmetric environment around the zinc atom, resulting in a non-superposable mirror image. Thus, this molecule is chiral. (e) A typical golf club: A typical golf club consists of a head, a shaft, and a grip. There is a side with the clubface and a side without. Thus, its mirror image is not superimposable, making it chiral.

Step 2: Answer the Exercise

After analyzing each object, we can now answer the question: (a) A left shoe: Chiral (b) A slice of bread: Not Chiral (c) A wood screw: Chiral (d) A molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\): Chiral (e) A typical golf club: Chiral

Key Concepts

Symmetry

Symmetry is a key factor in determining whether an object is chiral or not. An object is said to be symmetric if one side is an exact mirror image of the other. For example, a slice of bread typically has symmetry along its vertical axis, which means both halves look identical when mirrored. This symmetry implies that the object is not chiral: it can be superimposed on its mirror image. In contrast, objects like a left shoe lack such symmetry. Since a left shoe can't perfectly match the shape of a right shoe upon mirroring, it's considered chiral. Symmetry, therefore, plays an essential role in understanding chiral versus achiral objects, helping us identify if the object's mirror image is superimposable or not.

Molecular Models

Molecular models help visualize the structure of compounds, highlighting aspects like bonding and spatial arrangement, critical in understanding chirality. Take, for instance, a molecular model of \(\mathrm{Zn}(‍mathrm{en})\mathrm{Cl}_2\). This model displays zinc at the center surrounded by chloride ions and ethylenediamine ligands. The asymmetry introduced by the ligands prevents the molecule from being superimposed onto its mirror image, showcasing its chiral nature.
Molecular models aid significantly in organic chemistry for illustrating how molecules rotate and project in three dimensions. They are valuable tools for students to gain deeper insight into molecular shapes and how certain configurations give rise to chirality, affecting even properties like the way these molecules interact with polarized light.

Chiral Molecules

Chiral molecules are important in various scientific fields because they have non-superimposable mirror images, much like left and right hands, hence the term 'chiral' from Greek 'kheir' meaning hand. These molecules differ in orientation, which can significantly impact their chemical behavior. A classic example is found in pharmaceuticals, where the chirality of a drug molecule can determine its efficacy or toxicity.
The mundane world also intersects with chirality. For instance, a typical wood screw, while not a molecule, is chiral because it cannot be aligned with its mirror image due to its spiral structure. Recognizing chiral molecules and structures involves a keen understanding of spatial arrangement, making this concept vital in chemistry and beyond.

Mirror Image

Understanding the concept of a mirror image is essential in grasping chirality. A mirror image refers to the reflection of an object, much like what you see when you hold an item up to a mirror. For chiral objects, these mirror images are non-superimposable, meaning they cannot be placed on top of each other to give the same object.
Consider a golf club: when you look at its reflection, it looks the same only if the image is flipped back, indicating it is chiral. Similarly, in molecular chemistry, the difference in the spatial arrangement of atoms makes chiral molecules unable to line up with their mirrors. This property is pivotal as it can define how molecules interact with biological systems or how they function in a chemical reaction.