Problem 83 - General Chemistry: Principles and Modern Applications

Question

In the monochlorination of hydrocarbons, a hydrogen atom is replaced by a chlorine atom. How many different monochloro derivatives of 2 -methylbutane are possible?

Step-by-Step Solution

Answer

The number of possible monochloro derivatives of 2-methylbutane is 3.

Step 1: Draw the structure of 2-methylbutane

Identify the structure of 2-methylbutane. It's a five-carbon chain with a methyl group (an extra carbon) attached to the second carbon. Write the structure out and mark each hydrogen atom.

Step 2: Identify positions for chlorination

Identify unique positions where hydrogen atoms can be replaced by a chlorine atom. There are three unique positions: one on the end carbon atom (primary carbon), one on the second carbon atom (tertiary carbon), and one on the middle carbon atom (secondary carbon).

Step 3: Count the derivatives

Count the number of different monochlorinated products that can be formed by replacing a hydrogen atom at each position. Each unique position leads to a different structural isomer. Therefore, replacing a hydrogen atom at each of these positions produces a total of 3 unique monochloro derivatives of 2-methylbutane.

Key Concepts

Monochlorination

Monochlorination is a type of chemical reaction where one hydrogen atom in a hydrocarbon is replaced by a chlorine atom. This reaction is fundamental in organic chemistry because it changes the properties of the original compound. Imagine you have a simple hydrocarbon chain, and the monochlorination process introduces a chlorine atom, making a new substance with potentially very different chemical behaviors.

Most often, monochlorination occurs in the presence of light or heat as these conditions create free radicals which facilitate the reaction. The radical mechanism involves several steps:

• Initiation: The chlorine molecule is split into two radicals by light or heat.
• Propagation: The chlorine radical reacts with the hydrocarbon, removing a hydrogen atom and creating a hydrocarbon radical.
• Termination: Two radicals combine to stabilize the reaction.

Understanding monochlorination and its reaction conditions can help in predicting and explaining the resulting products when organic compounds interact with chlorine.

Isomers

Isomers are molecules with the same molecular formula but different structures. This means that they have the same types and numbers of atoms but arranged differently. Isomers are crucial because they can have vastly different chemical and physical properties even though they are made up of the same elements.

In the context of monochlorination, each potential position of chlorination on the hydrocarbon chain can yield different isomers. For example, chlorinating different positions on a structure like 2-methylbutane results in different structural isomers representing each possible monochlorinated product.

To identify isomers, one must look at the carbon skeleton and recognize possible positions for substitutions, like the hydrogens that can be replaced by a chlorine atom. Recognizing and naming these isomers is an essential skill in organic chemistry.

2-methylbutane derivatives

2-methylbutane is an interesting molecule because it serves as a base structure for the creation of multiple derivatives. In terms of its structure, it consists of a five-carbon chain with a methyl group attached to the second carbon. This offers several distinct positions where substitution reactions can occur.

When undergoing monochlorination, different products, or derivatives, form based on which hydrogen atom is replaced. Each position yields a unique compound because of the spatial arrangement of the atoms:

• Chlorinating the primary carbon results in one derivative.
• Chlorinating the tertiary carbon gives another isomer.
• Chlorinating a secondary carbon leads to yet another unique derivative.

Thus, in the case of 2-methylbutane, there are three possible monochlorinated derivatives due to the different possible positions of chlorination. This highlights the diversity in organic chemistry where seemingly similar compounds show distinct characteristics based on their structure.