Question

The number of possible enantiomeric pairs that can be produced during monochlorination of 2 -methyl butane are: (a) 2 (b) 3 (c) 4 (d) 1

Short answer

Only 1 enantiomeric pair is possible: (d) 1.

Step-by-step solution

Understand the Molecular Structure

2-methylbutane, also known as isopentane, has a carbon chain with four carbons and a methyl group attached to the second carbon. Its structural formula is CH3-CH(CH3)-CH2-CH3.

Identify Possible Chlorination Sites

Identify the different carbon atoms that can be chlorinated. In 2-methylbutane, there are three unique carbon atoms: the primary carbon (C1), the secondary carbon (C2), and another primary carbon (C3). The terminal carbon (C4) is equivalent to C1 due to symmetry.

Determine Chiral Centers Formation

Check if chlorination at any of these positions forms a chiral center. Chlorination at the secondary carbon (C2) will result in the formation of a chiral center, as it is bonded to four different groups post-chlorination.

Count the Enantiomeric Pairs

Since only chlorination at C2 results in a chiral molecule, only one pair of enantiomers (optical isomers) is possible. Chlorination at other sites does not introduce chirality to the molecule.

Key concepts

Stereochemistry

Stereochemistry is a fascinating area of organic chemistry that deals with the 3D arrangement of atoms in molecules. It's crucial because this arrangement can significantly influence the behavior and reaction of the molecules. Depending on how atoms are oriented in space, two molecules with the same molecular formula can have vastly different properties. A key part of stereochemistry involves the study of isomers, compounds that have the same formula but their atoms are arranged differently. Understanding stereochemistry helps chemists predict how molecules interact in biological systems, which directly impacts the development of pharmaceuticals and other essential compounds.

Chiral Centers

A chiral center is a carbon atom that is attached to four different atoms or groups. This unique arrangement allows for two non-superimposable mirror images of the molecule, a characteristic feature of chiral centers. In organic chemistry, identifying chiral centers in a compound is essential for understanding its potential to exist as enantiomers. Chiral centers play a vital role in determining the molecule's optical activity, which is its ability to rotate plane-polarized light. This property is not only significant in lab settings but also in nature and industries where optical purity can influence the effectiveness of substances.

Enantiomers

Enantiomers are a type of stereoisomer where two molecules are non-superimposable mirror images, much like your left and right hands. These enantiomers usually have identical physical properties except for their interaction with polarized light and other chiral substances. This becomes particularly important in biological systems, where typically only one enantiomer of a molecule is biologically active. Recognizing and synthesizing the correct enantiomer is critical in pharmaceuticals, as the wrong one can be ineffective or even harmful. In the context of 2-methylbutane, enantiomers arise only when a chiral center is present, leading to one pair of enantiomers upon chlorination at a specific site.

Monochlorination

Monochlorination is a type of halogenation reaction where only one hydrogen atom in a compound is replaced by a chlorine atom. This process helps in the alteration of chemical properties, creating new compounds. The outcome of a monochlorination reaction largely depends on which hydrogen is replaced. For 2-methylbutane, chlorination can occur at different carbon atoms, but only chlorination at the secondary carbon can result in the formation of a chiral center and consequently enantiomers. This selective chlorination is a fundamental example of how reactions can be directed to yield specific molecular structures and is a key concept in many synthetic chemistry processes.

2-Methylbutane

2-Methylbutane is an organic compound known as an alkane with the chemical formula C₅H₁₂. It is part of the alkane series and is also referred to as isopentane. This compound has a branched structure, with a methyl group attached to the second carbon of a butane backbone. 2-Methylbutane serves as an ideal example for studying concepts like stereochemistry and chiral centers due to its simple structure and the ability to undergo monochlorination. Understanding the arrangement and reactivity of 2-methylbutane provides insights into more complex organic reactions and helps illustrate key concepts in stereochemistry effectively.