Question

Draw the structure of the product of the reaction of chlorine with but-2-ene.

Short answer

The product is 2,3-dichlorobutane.

Step-by-step solution

Understand the Reaction Type

Chlorine reacting with but-2-ene is an example of an electrophilic addition reaction. In this type of reaction, the pi bond of the alkene reacts with chlorine, resulting in the formation of a dihalogenated alkane.

Analyze the Reactants

But-2-ene is a four-carbon alkene with the double bond located between the second and third carbons. The molecular structure can be represented as CH3-CH=CH-CH3. Chlorine (Cl2) is a diatomic molecule.

Addition of Chlorine to the Alkene

In electrophilic addition, the chlorine molecule will react with the double bond of but-2-ene. The pi electrons from the double bond attack one of the chlorine atoms, forming a three-membered chloronium ion intermediate. This intermediate opens up, allowing the second chlorine atom to bond to the opposite carbon.

Draw the Product

The resulting product will have the initial double bond replaced by a single bond, with each of the carbons formerly involved in the double bond now bonded to a chlorine atom. The product is 2,3-dichlorobutane with the structure: CH3-CHCl-CHCl-CH3.

Key concepts

Alkene Reactions

Alkene reactions are a fascinating part of organic chemistry due to their versatile nature. Alkenes are hydrocarbons that contain at least one carbon-carbon double bond, symbolized as \(C=C\). This double bond is key to their reactivity. In reactions, the electrons in the pi bond are often attacked by electrophiles – positively charged agents attracted to electrons – in what is known as an electrophilic addition reaction.
During these reactions, the double bond is broken and two new single bonds are formed in its place. This allows alkenes to undergo transformations that result in a wide variety of products, depending on the electrophile involved. One common example is the reaction between an alkene and a halogen, like chlorine or bromine, where a dihaloalkane product is typically formed.
In summary, understanding alkene reactions is crucial as they serve as building blocks for synthesizing more complex organic molecules.

Chlorination of Hydrocarbons

Chlorination is a specific type of halogenation where chlorine atoms are introduced into a hydrocarbon. When alkenes, which contain a double bond, are chlorinated, it usually occurs through an electrophilic addition mechanism. This means the chlorine molecule gets added across the double bond.
Here’s how it happens: The \(Cl_2\) molecule approaches the electron-rich double bond. This bond initiates the reaction by breaking into one chlorine ion that forms an intermediate, often a chloronium ion. Then, the second chlorine atom attaches to the opposite carbon of the double bond position, completing the addition.
The process is efficient and typically results in the formation of a dihalogenated alkane. Chlorination is a significant reaction in organic synthesis as it helps in modifying hydrocarbons and introducing chlorine functionalities into organic compounds. Knowing the structure of the resulting compound helps chemists predict reactivity and interactions with other substances.

Dihalogenated Alkane Formation

The formation of dihalogenated alkanes is a direct result of the electrophilic addition reactions of alkenes with halogens. When chlorine is added to an alkene, each of the double-bonded carbons receives one chlorine atom, resulting in a molecule with two halogen atoms, known as a dihalogenated alkane.
Consider the reaction of but-2-ene with chlorine: the original double bond between the second and third carbons in but-2-ene is replaced by chlorines, forming 2,3-dichlorobutane.
The importance of dihalogenated alkanes lies in their significance in various chemical industries, including pharmaceuticals and agrochemicals. Their formation can greatly alter the chemical properties, reactivity, and profile of the original hydrocarbon, providing diverse pathways for further chemical transformations and applications.