Question

Addition of IIC \(l\) to 2 -methyl-2-butenc mainly gives (1) 1 -chloro-2-methyl butanc (2) 2-chloro-2-methyl butanc (3) 2-chlorobutanc (4) 1-chlorobutane

Short answer

2-chloro-2-methyl butane

Step-by-step solution

Understand the Reaction

This is an electrophilic addition reaction in which HCl is added to 2-methyl-2-butene, which is an alkene.

Identify the Reactants and the Product

The reactants are 2-methyl-2-butene and HCl. The product is a chloroalkane (an alkane with a chlorine atom).

Determine the Major Product

According to Markovnikov's rule, the hydrogen atom from HCl will add to the carbon of the double bond with the most hydrogen atoms already attached. This leads to the formation of the most stable carbocation intermediate.

Form the Carbocation Intermediate

The double bond in 2-methyl-2-butene breaks, and a carbocation is formed. The more stable carbocation is a tertiary carbocation at the 2-position (because the carbon with the most alkyl groups leads to greater stability).

Formation of the Final Product

The chlorine atom will attach to the carbon that has the positive charge, which in this case is the 2-position.

Identify and Confirm the Product

The major product is 2-chloro-2-methyl butane as it follows Markovnikov's rule and forms the most stable intermediate.

Key concepts

Markovnikov's Rule

In organic chemistry, Markovnikov's rule helps us predict the outcome of electrophilic addition reactions. According to this rule, during the addition of HX (where X is a halogen) to an alkene, the hydrogen (H) attaches to the carbon with more hydrogen atoms. This means the halogen (X) attaches to the carbon with fewer hydrogen atoms.
In our exercise, HCl adds to 2-methyl-2-butene. The double bond breaks, and H attaches to the carbon with more hydrogens, leading to a more stable intermediate.
Understanding Markovnikov's rule is important for predicting the major product in addition reactions!

Carbocation Stability

Carbocation stability is a key concept in electrophilic addition reactions. A carbocation is a positively charged carbon atom. The stability of a carbocation impacts the product of a reaction and follows this order: tertiary > secondary > primary.
In our reaction, when HCl adds to 2-methyl-2-butene, the double bond breaks and forms a carbocation. The most stable carbocation forms at the tertiary carbon (2-position) because it is surrounded by more alkyl groups. These groups donate electron density, stabilizing the positive charge.
Recognizing the stability of carbocations helps us predict which intermediate will form in a reaction.

Chloroalkanes

Chloroalkanes are alkanes with one or more chlorine atoms attached. They are the products of reactions like the addition of HCl to alkenes.
In our example, 2-chloro-2-methyl butane forms as the major product. Here's the breakdown:

• HCl adds to 2-methyl-2-butene
• Markovnikov's rule directs the H to attach to the carbon with more hydrogens
• This forms a stable tertiary carbocation at the 2-position

The chlorine then attaches to this carbon, creating 2-chloro-2-methyl butane.
This chloroalkane is important in both organic synthesis and industrial applications.

Alkenes

Alkenes are hydrocarbons with at least one carbon-carbon double bond. They are more reactive than alkanes due to this bond.
In electrophilic addition reactions, the double bond is crucial since it can break and form new bonds. For example, in the given exercise:

• 2-methyl-2-butene, an alkene, reacts with HCl
• The double bond breaks, allowing HX to add across it

This breakage and formation depend on the reactants and conditions.
Understanding alkenes is essential as they are starting materials in many organic reactions, such as polymerization and alkylation.