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Finish Solved Problem 7-3 by showing how the rearranged carbocations give the four products shown in the problem. Be careful when using curved arrows to show deprotonation and/or nucleophilic attack by the solvent. The curved arrows always show movement of electrons, not movement of protons or other species.

Short Answer

Expert verified

E1 mechanism or E1 elimination involves two steps—ionization and deprotonation. During ionization, intermediate carbocation is formed; and in deprotonation, a proton is lost by carbocation. This happens in the presence of a base which leads to formation of double bond. Carbocation formation is the slow and rate-determining step of this reaction.

Methanol can act as base as well as nucleophile. Thus, when it acts as a base, it abstracts the proton from carbon which is adjacent to the carbocation, and on charge neutralisation of carbocation, a double bond or E1 products are formed.

Formation of E1 products

Step by step solution

01

Step by step solution:  Step 1: Formation of E1 products

E1 mechanism or E1 elimination involves two steps—ionization and deprotonation. During ionization, intermediate carbocation is formed; and in deprotonation, a proton is lost by carbocation. This happens in the presence of a base which leads to formation of double bond. Carbocation formation is the slow and rate-determining step of this reaction.

Methanol can act as base as well as nucleophile. Thus, when it acts as a base, it abstracts the proton from carbon which is adjacent to the carbocation, and on charge neutralisation of carbocation, a double bond or E1 products are formed.

Formation of E1 products

02

Step-2. Formation of  products:

reaction mechanism follows three steps. Firstly a carbocation is formed from the removal of leaving group, halogen. Then, carbocation is attacked by the nucleophile. Lastly, deprotonation takes place which gives the required product.

Methanol acts as nucleophile and attacks the carbocation which leads to formation of product. There is no rearrangement of carbocation as formed carbocations are stable.

Formation of products

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Most popular questions from this chapter

Give the substitution and elimination products you would expect from the following reactions.

  1. 3-bromo-3-ethylpentane heated in methanol
  2. 1-iodo-1-phenylcyclopentane heated in ethanol
  3. 1-bromo-2-methylcyclohexane + silver nitrate in water (forces ionization)

A double bond in a six-membered ring is usually more stable in an endocyclic position than in an exocyclic position. Hydrogenation data on two pairs of compounds follow. One pair suggests that the energy difference between endocyclic and exocyclic double bonds is about

9 KJ/mol. The other pair suggests an energy difference of about

5 KJ/mol. Which number do you trust as being more representative of the actual energy difference? Explain you answer.

Question: Give systematic (IUPAC) names of the following alkenes.

(a)

(b)

(c)

(d)

(e)

(f)

For each reaction, decide whether substitution or elimination (or both) is possible, and predict the product you expect. Label the major products.

(a) 1 - bromo - 1 - methylcyclohexane + NaOH in acetone

(b) 1 - bromo - 1 - methylcyclohexane + triethylamine (Et3N:)

(c) chlorocyclohexane + NaOCH3 in CH3OH

(d) chlorocyclohexane + NaOC(CH3) in (CH3)3COH

Propose mechanisms and draw reaction-energy diagrams for the following reactions. Pay particular attention to the structures of any transition states and intermediates. Compare the reaction-energy diagrams for the two reactions and explain the differences.

  1. 2-Bromo-2-methylbutane reacts with sodium methoxide in methanol to give 2-methylbut-2-ene (among other products).
  2. 2-Bromo-2-methylbutane reacts in boiling methanol to give 2-methylbut-2-ene (among other products).
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