Chapter 8, Problem 8.61P

Interpretation Introduction

(a)

Interpretation:

The complete, detailed mechanism for the reaction is to be drawn that follows an $\text{E1}$ reaction pathway.

Concept introduction:

$\text{E1}$ reaction is a unimolecular elimination reaction which takes place in two steps. In the first step, the bond between the carbon atom and the leaving group breaks to generate a carbocation, which is known as a heterolysis step. In the second step, a base removes a proton, forming an alkene. A proton transfer reaction is handy and can be incorporated in the mechanism of an $\text{E1}$ elimination to avoid the formation of incompatible species. In case of strong acidic reaction conditions, the first preferred step is a proton transfer reaction to protonate the $\text{OH}$ group in alcohols. Energy in the form of heat is provided for an endothermic reaction. A proton transfer reaction is handy and can be used in the reaction mechanism so as to avoid generation of non-compatible species that would interfere with the reaction medium.

Interpretation Introduction

(b)

Interpretation:

Free energy diagram that agrees with the mechanism in part a) is to be drawn labeling overall reactants, overall products, all transition states, and all intermediates.

Concept introduction:

$\text{E1}$ reaction is a unimolecular elimination reaction, which takes place in two steps. In the first step, the bond between the carbon atom and the leaving group breaks to generate a carbocation, which is known as a heterolysis step. In the second step, a base removes a proton, forming an alkene. The free energy diagram is a plot of free energy vs reaction coordinates. As $\text{E1}$ reaction occurs in two steps, there are two transition states with one intermediate which supports the mechanism. The overall reactants are shown on the far left; the overall products are shown on the far right, and the intermediates appear at the local energy minimum in between.