8-34c - Organic Chemistry (Mcmurry)

Question

Iodine azide, , adds to alkenes by an electrophilic mechanism similar to that of bromine. If a monosubstituted alkene such as 1-butene is used, only one product results:

c) 

In light of the result observed when ,adds to 1-butene, what is

the polarity of the bond? Propose a mechanism for the reaction

using curved arrows to show the electron flow in each step.

Step-by-Step Solution

Answer

Polarity of bond is:

$$\begin{gathered} \mathrm{I}-{\mathrm{N}}_3 \\ \mapsto \end{gathered}$$

Mechanism for the reaction is:

Markovnikov’s Rule

When we do electrophilic addition reaction on an alkene we get two different products out of which one is major product and another one is minor product. Major products and minor products are formed on the basis of stability of carbocation. In case of more stable carbocation, we will get major product and in case of less stable carbocation we will get minor product. On the basis of this Vladimir Markovnikov had published Markovnikov’s rule. Which states that when an electrophile adds up on an asymmetrical alkene that will add up on the carbon atom having more number of hydrogen atoms.

Example

                      Example of Markovnikov’s rule

In this hydrogen ion is an electrophile and according to Markovnikov’s rule it will add up on that carbon atom which is having more number of hydrogens and is a nucleophile it will add on that carbon atom having less number of hydrogen atoms. 

Mechanism of the reaction

Polarity of any bond is defined by charge separation. Polarity difference is there or we can say that a bond is polar when one atom is having partial positive charge and other atom is having partial negative charge. Direction of polarity of any bond is from positive to negative end. 

$$\begin{gathered} \mathrm{I}-{\mathrm{N}}_3 \\ \mapsto \end{gathered}$$

Step by step mechanism of the reaction is:

Step 1: Double bond of asymmetric alkene will attack on an electrophile ()

Step 2: The nucleophile that has released in first step will now attack on the carbon atom. In this step concerted reaction will take place i.e. breaking of bond and formation of bond will take place simultaneously. 

Step 3: We will get the product as defined in Markovnikov’s rule.

                            Mechanism of the reaction