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

Objects (a) a left shoe, (c) a wood screw, and (e) a typical golf club are chiral. Objects (b) a slice of bread and (d) a molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\) are not chiral.

Step-by-step solution

(Examine object (a): a left shoe)

First, consider the object 'a' - a left shoe. Imagine its mirror image and try to fit it onto the original shoe. They don't perfectly fit, as the original is made for the left foot and the mirror image is made for the right foot. Therefore, a left shoe is chiral.

(Examine object (b): a slice of bread)

Next, consider object 'b' - a slice of bread. Most slices of bread have an irregular shape. However, if you can find a symmetric slice or align the mirror image with the original bread slice, then it is not chiral. In this case, we assume a typical slice of bread could be superimposed on its mirror image and think that the slice of bread is not chiral.

(Examine object (c): a wood screw)

Now, let's look at object 'c' - a wood screw. A wood screw has a helical shape, which rotates in a particular direction. Its mirror image will have a helix that rotates in the opposite direction, and hence the two cannot be superimposed. Therefore, a wood screw is chiral.

(Examine object (d): a molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\))

The given molecular complex is \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\). By analyzing the chemical structure and composition of the atoms present in this complex, we can determine if there is any asymmetric center or not. In this complex, due to the ionic nature of the bond between Zn and Cl, the entire complex is symmetric in nature, and hence not chiral.

(Examine object (e): a typical golf club)

Finally, let's look at object 'e' - a typical golf club. A golf club has a specific orientation, with the head designed to hit the golf ball. The mirror image of a golf club will have the head in the opposite orientation, thus rendering them impossible to superimpose. Therefore, a typical golf club is chiral. Step 2: Summarize results

(Summary of chiral objects)

From our analysis, we can conclude that objects (a) a left shoe, (c) a wood screw, and (e) a typical golf club are chiral, while objects (b) a slice of bread and (d) a molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\) are not chiral.

Key concepts

Stereochemistry

Stereochemistry is the branch of chemistry that studies the spatial arrangement of atoms in molecules and the impact of this arrangement on the chemical and physical properties of substances. This concept plays an integral role in understanding how molecules interact with each other and with biological systems.

Take the example of object (a), a left shoe, which is considered chiral. In stereochemistry, this relates to molecules where the spatial arrangement cannot be superimposed onto its mirror image, much like a left shoe cannot be superimposed onto a right shoe. Chirality in chemistry is often due to the presence of an asymmetric carbon atom, but it can also arise from a lack of symmetry in the molecule's structure.

In understanding and applying stereochemistry, especially in organic compounds, it's crucial to recognize chirality because it can affect the way a molecule behaves – particularly in biological systems where enzymes and receptors are also chiral.

Molecular Symmetry

Molecular symmetry refers to the balanced distribution of the molecule's components that allows for operations like rotations or reflections without altering the molecule's appearance. The concept of symmetry helps to classify molecules, predict their properties, and understand their reactivity.

In step 4, the molecular model of \(\mathrm{Zn}(\mathrm{en})\mathrm{Cl}_{2}\) exhibited symmetry that made it non-chiral. Symmetry elements, such as planes of symmetry, centers of inversion, and rotational axes, serve as tools to determine the symmetry operations a molecule can undergo. If an object or a molecule has one or more such elements, it is likely to be achiral. In this case, the ionic bonds between zinc and chloride ions create an arrangement that possesses symmetry, meaning any mirror image could be superimposed onto the original, hence non-chiral.

Optical Isomerism

Optical isomerism is a form of stereoisomerism where isomers—molecules with the same molecular formula—differ in the way they affect polarized light. Chiral molecules have this property where they can rotate the plane of polarized light, with one enantiomer (isomer) rotating it in one direction and the other enantiomer rotating it in the opposite direction. These are termed as levorotatory and dextrorotatory isomers, respectively.

This property is particularly important in pharmaceuticals, as different enantiomers of a drug can have significantly different biological activities. For example, one enantiomer may be therapeutic, while the other could be harmful. This attribute is not found in achiral molecules, such as the slice of bread from object (b), as their mirror images are superimposable and they do not show optical activity. As a result, they do not rotate the plane of polarized light. The study of optical isomerism enhances the understanding of the profound implications stereochemistry can have on real world applications.