Chapter 7, Problem 64P

(a)

Interpretation Introduction

Interpretation: Out of the two indicated brominated system the one molecule that would undergo $\text{E2}$ reaction on treatment with sodium ethoxide in ethanol should be identified and explained.

  

Concept introduction: Experimental evidence for $\text{E2}$ mechanism pathway suggests that it readily occurs if the leaving group with respect to the proton is in anti- orientation in stable chair conformation. For instance, when $\text{cis-1-bromo-4-}\left(\text{1,1-dimethylethyl}\right)\text{cyclohexane}$ is treated with a strong base it leads to faster bimolecular elimination to afford the corresponding alkene relative to $\text{trans-1-bromo-4-}\left(\text{1,1-dimethylethyl}\right)\text{cyclohexane}$ . This is because in the transition state for $\text{E2}$ elimination as illustrated below:

  

(b)

Interpretation Introduction

Interpretation:Whether anti or syn elimination occurs in the indicated reactions should be written.

  

Concept introduction: Experimental evidence for $\text{E2}$ mechanism pathway suggests that it readily occurs if the leaving group with respect to the proton is in anti- orientation in stable chair conformation. For instance, when $\text{cis-1-bromo-4-}\left(\text{1,1-dimethylethyl}\right)\text{cyclohexane}$ is treated with a strong base it leads to faster bimolecular elimination to afford the corresponding alkene relative to $\text{trans-1-bromo-4-}\left(\text{1,1-dimethylethyl}\right)\text{cyclohexane}$ . This is because in the transition state for $\text{E2}$ elimination as illustrated below: