Question

Consider the following statements: (1) Racemic forms are not optically active but are resolvable (2) The presence of chiral atom is sufficient but not the necessary condition for enantiomer (3) Meso compounds are inactive and are not resolvable (4) Conformational enantiomers can be resolved Now select the correct statements. (a) 1,2 and 3 (b) 2,3 and 4 (c) 1,2 and 4 (d) \(1,2,3\) and 4

Short answer

The correct statements are (1), (2), and (3). The answer is (a).

Step-by-step solution

Analyze Statement 1

Statement (1) says that racemic forms are not optically active but are resolvable. Racemic mixtures contain equal amounts of two enantiomers, making them optically inactive. However, they can be separated or resolved into the individual enantiomers. This statement is correct.

Evaluate Statement 2

Statement (2) suggests that the presence of a chiral atom is sufficient but not necessary for a compound to be an enantiomer. Enantiomers are non-superimposable mirror images, typically involving a chiral center, but some chiral compounds may lack a chiral atom. Therefore, this statement is also correct.

Consider Statement 3

Statement (3) claims that meso compounds are inactive and not resolvable. Meso compounds are optically inactive due to an internal plane of symmetry and can't be separated into enantiomers. Hence, this statement is correct.

Investigate Statement 4

Statement (4) states that conformational enantiomers can be resolved. Conformational isomers differ only by rotation about single bonds. Normally, they equilibrate too quickly at room temperature, making them irreparable to resolution. Hence, this statement is incorrect as only relatively stable conformers could potentially be resolved under special conditions.

Key concepts

Racemic Mixtures

Racemic mixtures are intriguing because they provide insight into chirality and optical activity. A racemic mixture contains equal amounts of left and right-handed enantiomers, molecules that are non-superimposable mirror images. Since the optical activities of these enantiomers cancel each other out, a racemic mixture is optically inactive. This means it cannot rotate plane-polarized light. However, racemic mixtures can be resolved, or separated, into their individual optically active enantiomers. This process is crucial in many applications, especially in pharmaceuticals, where the activity of enantiomers can differ dramatically.

Chiral Centers

A chiral center is a carbon atom attached to four distinct groups, resulting in non-superimposable mirror images, also known as enantiomers. The presence of a chiral center often leads to chirality, which is an essential concept in stereochemistry. However, having a chiral center is sufficient but not necessary to have an enantiomer. Some molecules exhibit chirality due to their shape or the presence of an axis of asymmetry without needing a traditional chiral center. Understanding chiral centers is key to grasping the broader topic of stereochemistry in organic compounds.

Meso Compounds

Meso compounds are a fascinating exception in stereochemistry. Despite having multiple chiral centers, a meso compound is optically inactive due to an internal plane of symmetry. This symmetry allows for the equal and opposite cancellation of rotational effects of each chiral center, leaving the compound optically inactive. Because they are superimposable on their mirror images, meso compounds are not resolvable into separate enantiomers. The concept illuminates how symmetry can influence optical activity in seemingly complex structures.

Conformational Isomerism

Conformational isomerism involves isomers that can be interconverted through rotations around single bonds. This flexibility plays a huge role in the functionality and three-dimensional shape of molecules. Conformational isomers, or conformers, often equilibrate swiftly at room temperature, which usually prevents their resolution into stable configurations. However, under certain conditions that restrict rotation, it is possible to isolate and resolve conformational enantiomers. Understanding this concept is vital for comprehending molecular dynamics, particularly in biological and chemical reactions where such flexibility can influence reactivity and interactions.