Question

The compound 2,3 -dibromo-2-methylhexane is formed by addition of \(\mathrm{Br}_{2}\) to an alkene. Identify the alkene, and write an equation for this reaction.

Short answer

The alkene is 2-methylhex-2-ene and the reaction is: \[ \text{2-methylhex-2-ene} + \mathrm{Br}_2 \rightarrow \text{2,3-dibromo-2-methylhexane} \]

Step-by-step solution

Understand the Reaction Type

The question involves the formation of 2,3-dibromo-2-methylhexane by the addition of bromine ( \(\mathrm{Br}_{2}\)) to an alkene. This is an example of an electrophilic addition reaction where an alkene reacts with a halogen to form a vicinal dibromide.

Determine the Structure of Product

Examine the structure of the given product, 2,3-dibromo-2-methylhexane. It consists of bromine atoms attached to the 2nd and 3rd carbon atoms, with a methyl group also attached to the 2nd carbon of the hexane chain.

Identify the Corresponding Alkene

The original alkene must have had a double bond between the 2nd and 3rd carbon atoms to accommodate the addition of bromine atoms. Removing bromines gives 2-methylhex-2-ene as the original alkene. This alkene has the required double bond position and the methyl group on the 2nd carbon, matching the product's structure.

Write the Chemical Equation

Using the identified alkene, write the chemical equation: \[ \text{2-methylhex-2-ene} + \text{Br}_2 \rightarrow \text{2,3-dibromo-2-methylhexane}\] This equation represents the overall reaction of the alkene with bromine to form the dibromo compound.

Key concepts

Alkene Halogenation

Alkene halogenation is a fascinating reaction that involves the addition of halogens, like bromine (\(\text{Br}_2\)), to alkenes. Alkenes are hydrocarbons that contain at least one carbon-to-carbon double bond. When you expose them to halogens, they react to form halogenated compounds. This addition occurs when the halogen molecules are polarized as they approach the electron-rich double bonds of an alkene. As a result, a highly reactive species known as halonium ion forms, which then interacts with halide ions to give the final product.
This process is not only interesting, but it is also very important in organic chemistry as it forms the basis for understanding other addition reactions. It shows how reactive alkenes can be and how they interact with different molecules.
This reaction is very selective and depends on the structure of the original alkene, such as whether substituents like methyl groups are present. It is this reaction that transforms simple alkenes into more complex compounds, leading to a diverse range of applications in synthesizing new materials.
The essentials of halogenation thus play a critical role in both education and research, offering a window into more intricate chemical processes.

Vicinal Dibromides

Vicinal dibromides are the products of a halogenation reaction involving alkenes. The term 'vicinal' refers to the placement of two bromine atoms on adjacent carbon atoms within the same molecule. In the context of our reaction, when bromine was added to the double bond of an alkene, it resulted in two bromine atoms attaching themselves on the neighboring carbons, forming a vicinal dibromide.
Vicinal dibromides are interesting because, in addition to being essential products in electrophilic addition reactions, they are often intermediates or starting points for other chemical transformations. Chemists utilize them to introduce more functional groups into a molecule through further reactions.
These compounds are so named to highlight the proximity of the bromine atoms, distinguishing them from 'geminal' dibromides, where both bromines are on the same carbon. Being able to differentiate between these is important, as it affects both the chemical properties and potential reactions the compound can undergo.
The presence of vicinal dibromides in organic pathways not only confirms the mechanics of halogenation but also paves the way for deeper exploration of reaction mechanisms and the synthesis of structurally complex molecules.

Organic Reaction Mechanisms

Organic reaction mechanisms describe the step-by-step processes by which chemical reactions occur. Understanding these mechanisms is crucial for mastering organic chemistry, as they provide insights into why and how reactions take place.
In the case of alkene halogenation forming vicinal dibromides, the mechanism begins with the polarization of the bromine molecule as it nears the electron-rich double bond of the alkene. This polarization results in the formation of a cyclic bromonium ion intermediate, where one bromine atom is temporarily bonded to both carbons of the original double bond.
The next step involves the nucleophilic attack by the bromide ion (the remaining bromine ion) on one of the carbons in the bromonium ion. This leads to the formation of the vicinal dibromide, completing the electrophilic addition.
Detailing each stage of the mechanism is essential for students, as it helps them understand how changes in molecular structure facilitate chemical transformations. It demonstrates the predictable nature of reactions based on the properties of involved reagents and intermediates.
Exploring these organic mechanisms lays the foundation for tackling more complex reactions and syntheses in advanced chemistry studies, enlightening students about the elegant dance of molecular interactions.