Chapter 8, Problem 8.17P

Interpretation Introduction

Interpretation:

To draw the anti periplanar geometry for the E2 reaction and the product that results after elimination of HBr.

Concept introduction:

The most common mechanism for dehydrohalogenation is the E2 mechanism. An E2 reaction exhibits a second-order kinetics, in which the reaction is bimolecular and both the alkyl halide and the base appear in the rate equation. The most straightforward explanation for the second-order kinetics is a concerted reaction: all bonds are broken and formed in a single step. In other words simultaneously all bonds are broken and formed.

The transition state of an E2 reaction consists of four atoms from the alkyl halide-one hydrogen atom, two carbon atoms, and the leaving group (X)-all aligned in the same plane. There are two ways for the C-H and C-x bonds to be coplanar. When the H and X atoms oriented on the same side of the molecule. This geometry is called syn periplanar. While the H and X atoms oriented on opposite sides of the molecule. This geometry is called anti periplanar. The dihedral angle for the C-H and C-X bonds equals 0° for the syn periplanar arrangement and 180° for the anti periplanar arrangement.