Chapter 7, Problem 75PP

Interpretation Introduction

Interpretation:

Stereo isomers of given compound should be drawn and most reactive isomer is need to be find in E2 elimination reaction by using chair conformations.

Concept Introduction:

Chair conformer: chair conformer is a stable conformer for cyclohexane compound.  In this chair conformer two positions are important for substitutions one is equatorial and other one axial position. Axial positions are parallel to the axis of ring while equatorial positions are perpendicular to the axis of the ring.

Example:

  

After ring flip of the conformer, axial position becomes equatorial and equatorial position becomes axial.

Stereochemistry conversions in chair conformation are shown below.

  $\begin{array}{ccc}\begin{array}{l}Substituent\\ position\end{array}& cis& trans\\ 1,2position& \left(a,e\right)or\left(e,a\right)& \left(a,a\right)or\left(e,e\right)\\ 1,3position& \left(a,a\right)or\left(e,e\right)& \left(a,e\right)or\left(e,a\right)\\ 1,4position& \left(a,e\right)or\left(e,a\right)& \left(a,a\right)or\left(e,e\right)\end{array}$

E2 elimination reaction: E2 elimination occurs in a compound when the leaving group is antiperiplaner to the proton in presence of strong base.