Chapter 20.10, Problem 38ATS

Interpretation Introduction

Interpretation:

The structure should be design for beta –carotene.

Concept Introduction:

Witting reaction: When an aldehyde or ketone is treated with a witting reagent, a carbon – carbon is forming, and giving an alkene that exhibit the newly formed C=C bonding the location of the former carbonyl group.

Witting reaction mechanism:

This attack of phosphorous yield dictates the final product. the pathway with the least steric interaction is favored.

This process allows the preparation of an alkene by the reaction of an aldehyde ( $\text{-CHO}$) or ketone ( $\text{-C=O}$) with ylides generated from a phosphonium salt. The geometry of the resulting cis, Trans alkene depends on the reactivity of the ylide.

Schematic of the witting Reaction: Witting reagent :( ${\text{H}}_{\text{2}}{\text{C=PPh}}_{\text{3}}$), primary or secondary alkyl halide, ( ${\text{H}}_{\text{2}}{\text{C=PPh}}_{\text{3}}$), base, aldehyde, ketone. Product olefin.

$S_{N}1$Reaction: The $S_{N}1$ reaction is two-step process, leaving group leaves the molecule is first step and forms the more stable carbocation. Further, nucleophile attacks the carbocation and forms the final product in the second step. The rate of the reaction depends on the stability of the carbocation.

$S_{N}2$Reaction: The $S_{N}2$ reaction is single step process, leaving group leaves the molecule and nucleophiles attack the molecule is single step process which is simultaneous process.

Elimination Reaction: It is just reverse reaction of addition where substituent from the given molecule is removed via E1 (the reaction depends only on the substrate involved in the reaction) or E2 (the reaction depends on both of the substituents in the reaction) mechanismPCC reagent:

It is popularly known as Pyridinium chloromate. it’s generally used for come useful conversion.

Oxidation Reaction: The oxidation-reduction reaction is a type of chemical reaction it is involves a transfer of electrons between two species. In other words oxidation reaction number of a molecule atom or ion changes by gaining or losing electrons

To identify:-The given synthetic route to accomplish the target molecule transformation.