Chapter 17, Problem 17.20P

Interpretation Introduction

Interpretation:

The alkyl halide that could be used to synthesize the given Wittig reagent is to be given.

Concept introduction:

The Wittig reagent is prepared when an alkyl halide is treated with triphenylphosphine $\text{P}{\left({\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\right)}_{\text{3}}$ in a ${\text{S}}_{\text{N}}\text{2}$ mechanism. The product of the reaction is then treated with a strong base to generate Wittig reagent also known as phosphonium ylide. The reaction of Wittig reagent with aldehyde or ketone leads to the formation of an alkene $\left(\text{C=C}\right)$ product. In a Wittig reaction, the $\text{C}=\text{O}$ bond of a ketone or aldehyde is converted to a $\text{C}=\text{C}$ bond.

For an alkyl halide to be a suitable precursor for a Wittig reagent, the carbon atombonded to the leaving group (halide) must possess at least one hydrogen.