Question

The sex pheromones of the cigarette beetle "Lasioderma serricorne" is given below: How many chiral centres are present in serricorne? (A) 2 (B) 3 (C) 4 (D) 5

Short answer

The correct answer is (C) 4. The serricorne molecule has four carbon atoms that are each bonded to four distinct groups of atoms or groups, making them chiral centres. This conclusion is based on the process of identifying carbon atoms in a molecule, then checking how many of them are bonded to four distinct groups, and considering these as chiral centres. Thereupon, comparison with provided options indicates that the correct answer is four chiral centres.

Step-by-step solution

Definition of a Chiral Centre

In a molecule a chiral centre or a stereocentre is a carbon atom which is bonded to four different types of atoms or groups. The different groups around a carbon atom make the molecule non-identical to its mirror image, which is also called chirality.

Identify Carbon Atoms in the Molecule

The first step is to recognize the carbon atoms in the given structure of the molecule. In organic structures, lines represent bonds and the endings and intersections of these lines are the carbon atoms, except when another element is indicated.

Identify the Carbon Atoms Bonded to Four Distinct Groups

Here, the focus will be on identifying each carbon atom that is attached to four different atoms or groups. Each carbon atom should be examined separately, and the groups or atoms bonded to it identified.

Count the Number of Chiral Centres

After identifying the carbon atoms that are bonded to four different groups or atoms, these carbon atoms are counted. The number of these carbon atoms is the number of chiral centres.

Choose the Correct Answer

The number of chiral centres found in step 4 will correspond to one of the options given in the exercise, which will be the correct answer. Compare the number of chiral centres found with the options given and select the corresponding option. Please note that a complete solution requires the molecule's structural formula to determine the chiral centres. However, this process will allow the identification of chiral centres in any given organic molecule.

Key concepts

Chirality

Chirality is a fascinating concept in chemistry that revolves around the idea of a molecule not being identical to its mirror image. When you think of chirality, consider your hands. They are mirror images of each other, yet you can't superimpose one on the other perfectly—they are chiral. In organic chemistry, chirality often involves carbon atoms. When a carbon is bound to four different groups, it becomes a chiral center. This means the molecule can exist in two non-superimposable forms, known as enantiomers. These enantiomers have distinct chemical properties in biological contexts, often leading to one isomer working differently than the other, like offering different smells or biological activity. Understanding chirality is crucial for recognizing why two molecules with the same formula can behave differently in a body.

Stereochemistry

Stereochemistry refers to the study of spatial arrangement in molecules, especially focusing on how the arrangement affects the molecules’ properties and reactions. Every organic molecule can vary in the three-dimensional space, impacting how they interact with other molecules. Chirality, or having chiral centers, is an aspect of stereochemistry, where the arrangement around these asymmetric centers can lead to different outcomes.

• Enantiomers: Molecules that are mirror images
• Diastereomers: Molecules with multiple chiral centers with different configurations
• Conformers: Different structures that arise from rotations around single bonds

These differences mean that stereochemical configurations can affect whether enzymes can catalyze reactions, whether drugs will fit into a receptor, or even how effectively a smell is perceived. Recognizing and working with stereochemistry is essential in organic synthesis and pharmaceutical development.

Organic Molecules

Organic molecules are compounds primarily composed of carbon atoms, usually bonded to hydrogen, oxygen, nitrogen, or other carbon atoms. These molecules form the basis of life, being the framework for things such as proteins, carbohydrates, and DNA.
Organic molecules can vary vastly in size and complexity, leading to different functions and properties. One key feature of organic molecules is the versatility of carbon due to its ability to form four covalent bonds, allowing for countless structural possibilities.

• Aliphatic compounds: Straight or branched structures
• Aromatic compounds: Featuring rings with alternating single and double bonds

Understanding organic molecules and how they can form various complex structures is key for grasping broader concepts such as chirality and stereochemistry. Whether it's constructing polymers for materials or designing new drugs, the versatility of organic molecules opens up endless possibilities in science and industry.