Question

Which of the following have asymmetric carbon atoms? 1\. \(\mathrm{ClCH}_{2}-\mathrm{CH}_{2} \mathrm{Br}\) 2\. \(\mathrm{CH}_{3}-\mathrm{CHCl}_{2}\) 3\. \(\mathrm{CH}_{3}-\mathrm{CH} \mathrm{DCl}\) 4\. \(\mathrm{CH}_{2} \mathrm{Br}-\mathrm{CHOH}-\mathrm{CH}_{3}\) (a) \(1,2,3\) (b) \(1,3,4\) (c) 2,3 (d) 3,4

Short answer

The correct answer is (d): 3, 4.

Step-by-step solution

Understand Asymmetric Carbon Atoms

An asymmetric carbon atom is a carbon atom that is attached to four different groups. This property leads to chirality, which means that the molecule may have non-superimposable mirror images, commonly known as enantiomers.

Analyze Compound 1

Compound 1 is \(\mathrm{ClCH}_{2}-\mathrm{CH}_{2} \mathrm{Br}\). The first carbon is connected to two chlorine atoms and the second carbon is connected to another carbon, hydrogen, and bromine. Neither carbon has four different groups, so there are no asymmetric carbons here.

Examine Compound 2

Compound 2 is \(\mathrm{CH}_{3}-\mathrm{CHCl}_{2}\). The second carbon is connected to two chlorine atoms, one hydrogen, and one carbon. It does not have four different groups and thus is not asymmetric.

Investigate Compound 3

Compound 3 is \(\mathrm{CH}_{3}-\mathrm{CH} \mathrm{DCl}\). The second carbon is bonded to a hydrogen, a deuterium, a chlorine, and a methyl group. These are four different groups, indicating that this carbon is asymmetric.

Assess Compound 4

Compound 4 is \(\mathrm{CH}_{2} \mathrm{Br}-\mathrm{CHOH}-\mathrm{CH}_{3}\). The middle carbon is bonded to a bromine-hydrogen chain, an alcohol group, and a methyl group, making these three different groups along with its own hydrogen. Thus, this carbon is asymmetric.

Choose the Correct Answer

From Step 4 and Step 5, we determined that compounds 3 and 4 have asymmetric carbons. Therefore, the correct choice is option (d): 3, 4.

Key concepts

Chirality

Chirality is a fascinating concept in chemistry that relates to the three-dimensional arrangement of atoms. When a molecule has chirality, it means it exists in two forms that are mirror images of each other, much like your left and right hands. These mirror image molecules are not superimposable, which is what makes them unique.
Chirality arises when an organic compound contains an asymmetric carbon atom. This carbon is bonded to four different groups. When this occurs, the spatial arrangement leads to two distinct forms, which we call enantiomers. These enantiomers can have different chemical reactions and interactions in biological systems.

• Chirality is crucial in organic chemistry and biology.
• Only one enantiomer of a molecule might be biologically active.
• To determine chirality, one looks for an asymmetric carbon atom.

Recognizing the chirality of molecules is essential for understanding their chemical properties and how they interact in different environments, which can be highly relevant in the pharmaceutical industry.

Organic Chemistry

Organic chemistry is the study of carbon-containing compounds, which are fundamental to life on Earth. This branch of chemistry focuses on the structure, properties, composition, reactions, and synthesis of organic molecules. It is a vast subject, but one of its key concepts is the structure and chirality of molecules.
An asymmetric carbon atom in organic compounds indicates the presence of chirality. In organic chemistry, identifying these carbons helps chemists understand how molecules will behave in different reactions. Asymmetric carbons are like pivotal points in molecules that can make them 'handed', adding complexity and diversity to organic reactions.

• Organic chemistry revolves around hydrocarbons and their derivatives.
• It includes understanding how asymmetric carbon influences molecular behavior.
• The field is essential in developing drugs, plastics, fuels, and much more.

The analysis of asymmetric carbons in organic chemistry is critical, as it lays the groundwork for understanding more intricate behaviors of molecules, leading to advancements in industries like pharmaceuticals and materials science.

Enantiomers

Enantiomers are stereo isomers that are non-superimposable mirror images of each other. They occur when a molecule has an asymmetric carbon atom. In simple terms, think of enantiomers like a pair of shoes; the left and right shoes are mirrors, but you can't wear one on the other foot.
These molecules are important because even though they might look almost identical, they can have drastically different properties, especially in biological systems. This is because enantiomers interact with other chiral molecules, such as enzymes, in different ways.

• Enantiomers have identical physical properties except for the direction they rotate polarized light.
• Their biological activity can vary greatly.
• Pharmaceuticals often require specific enantiomers for effectiveness.

When defining enantiomers, it's key to consider applications in real-world chemistry and industry, where a specific enantiomer might be desirable or necessary for producing the desired effect, especially in drug development and formulation.