Among the given two molecules, the major product that is formed by 1 , 2 -addition of HCl to cyclopentadiene has to be found and explained. Concept Introduction: Addition reaction of dienes: The diene with a four carbon system is 1,3-butadiene . When it is allowed to react with two moles of HBr , it undergoes two type of addition reactions such as 1,2-addition and 1,4-addition as shown here: 1,3-butadiene reacts with H-Br and formed a resonance stabilized carbocation. The addition of a bromine atom to each of the two resonance forms has formed the corresponding product. So, two products are obtained. In one product the bromine atom has been attached to the 2 nd carbon atom indicating that it has been formed from 1,2-addition whereas in the other product, the bromine atom has been attached to the 1 st carbon atom indicating that it has been formed from 1,4-addition.

Question

4. a) Give a suitable rationale for the following cyclization, stating the type of process involved (e.g. 9-endo-dig), clearly showing the mechanistic details at each step. H CO₂Me 1) NaOMe 2) H3O® CO₂Me

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Question

Chapter 20, Problem 20.19P

Interpretation Introduction

Interpretation: Among the given two molecules, the major product that is formed by 1,2-addition of HCl to cyclopentadiene has to be found and explained.

Concept Introduction:

Addition reaction of dienes:

The diene with a four carbon system is 1,3-butadiene. When it is allowed to react with two moles of HBr, it undergoes two type of addition reactions such as 1,2-addition and 1,4-addition as shown here:

1,3-butadiene reacts with H-Br and formed a resonance stabilized carbocation. The addition of a bromine atom to each of the two resonance forms has formed the corresponding product. So, two products are obtained. In one product the bromine atom has been attached to the 2^nd carbon atom indicating that it has been formed from 1,2-addition whereas in the other product, the bromine atom has been attached to the 1^st carbon atom indicating that it has been formed from 1,4-addition.

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