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.

Short answer

The chiral objects in the given list are: (a) a left shoe, (c) a wood screw, and (e) a typical golf club.

Step-by-step solution

(a) Check if a left shoe is chiral

To determine if a left shoe is chiral, try to imagine its mirror image – a right shoe. If we put them on top of each other, they will never match perfectly because they have different shapes designed for different feet. Therefore, a left shoe is chiral.

(b) Check if a slice of bread is chiral

Visualize a slice of bread and its mirror image. A slice of bread, in general, is roughly symmetrical (assuming it is sliced evenly). Therefore, a mirror image of a slice of bread can be superimposed onto the original slice, or in other words, a slice of bread is achiral.

(c) Check if a wood screw is chiral

A wood screw and its mirror image have threadings that spiral in different directions. Therefore, they cannot be superimposed. Thus, a wood screw is chiral.

(d) Check if a molecular model of \(\mathrm{Zn}(\mathrm{en}) \mathrm{Cl}_{2}\) is chiral

The molecular model of \(\mathrm{Zn}(\mathrm{en}) \mathrm{Cl}_{2}\) is achiral, or not chiral, since it has an inversion center. It has two ethylenediamine (en) ligands that form a square planar geometry with two chloride ions around zinc. If we were to generate a mirror image of this molecular structure, it would be identical to the original structure.

(e) Check if a typical golf club is chiral

A typical golf club has an asymmetric shape that cannot be superimposed on its mirror image. This is because the clubface's angle and orientation vary depending on the type of golf club (right-handed or left-handed). Therefore, a typical golf club is chiral. In conclusion, the chiral objects from the list are: (a) a left shoe, (c) a wood screw, and (e) a typical golf club.

Key concepts

Mirror Image

When we talk about the mirror image of an object, we're thinking about what that object would look like if we held it up to a mirror. A mirror image flips the object as though you've rotated it, but in reality, the shape and form remain intact, just reversed. This is particularly important in understanding chirality. For instance, imagine a left shoe. Its mirror image is like having a right shoe.
- Each side is different yet closely related. - Flipping one over doesn't allow them to match.
In chemistry, molecules often have mirror images, and the ability to superimpose these images helps determine their chirality.

Asymmetry

Asymmetry refers to the lack of equality or equivalence between parts or aspects of something. It's an excellent way to test for chirality. If something is asymmetric, chances are it is chiral too. Take a typical golf club, for example. It is asymmetric and comes in either a left-handed or right-handed version.
- Asymmetry ensures the mirror image cannot overlap perfectly with the original. - The orientation differs, just like with our golf club or a left shoe.
In molecules, asymmetry often results in optical isomerism, where different forms of a molecule reflect light differently.

Superimposable Objects

Superimposable objects are those that can be placed over each other and match exactly. Consider a slice of bread. If it's perfectly even, its mirror image will sit over it comfortably without any mismatches. This means the object is achiral.
- Superimposable objects are mirror images that fit perfectly when one is placed on top of the other.- Most symmetric objects or molecules fit this category, like the \(\mathrm{Zn}(\mathrm{en}) \mathrm{Cl}_{2}\) molecule, making them achiral.
Understanding superimposability is crucial in determining if something is chiral or not.

Optical Isomerism

Optical isomerism essentially involves the rotation of plane-polarized light by some chiral molecules. When compounds have non-superimposable mirror images, they often display optical isomerism. Substances like sugar molecules can rotate light either to the left or to the right.
- This property stems from the chiral nature of the molecule. - It's a direct result of a molecule's three-dimensional arrangement and asymmetry.
It's important to study optical isomerism because it affects how molecules behave in nature and interact in various biological systems. Therefore, optical isomerism has crucial implications in pharmaceuticals and biochemistry.