Chapter 17, Problem 17.83P

Interpretation Introduction

Interpretation:

The complete, detailed mechanism as well as the major organic product for the given reaction is to be drawn.

Concept introduction:

In Wittig reaction, an aldehyde or ketone is treated with a phosphonium ylide (Wittig reagent) to form the corresponding alkene as the final product. Wittig reagent is formed when an alkyl halide is treated with triphenylphosphine [$\text{P}{\left({\text{C}}_{\text{6}}{\text{H}}_{\text{5}}\right)}_{\text{3}}$]. The halogen atom is replaced by the triphenylphosphine group via ${\text{S}}_{\text{N}}\text{2}$ mechanism. In the presence of a strong base, a triphenyl phosphonium ylide is formed. A Wittig reagent is highly nucleophilic at the carbon atom.

${}^{\text{13}}\text{C}$ NMR provides valuable information about the carbon skeleton. Each signal in the ${}^{\text{13}}\text{C}$ NMR equals the number of distinct carbon atoms in the given unknown. The saturated carbon atoms appear in the range $\text{δ}\text{0-35 ppm}$ if it is a simple alkane fragment. If it is attached to any electronegative element such as halogens or nitrogen, then the range is $\text{δ}\text{25-70 ppm}$. Triple bonded carbon atoms range from $\text{δ}\text{65-85 ppm}$. Alkene carbons range from $\text{δ}\text{105-150 ppm}$. Carbonyl carbon atoms in acids, esters, amides, and anhydrides range from $\text{δ}\text{120-185 ppm}$. Carbonyl carbons in aldehydes and ketones range from $\text{δ}\text{190-220 ppm}$. From the known molecular formula of the product, the index of hydrogen deficiency is calculated, which would help us to predict the unsaturation in the product molecule.