Chapter 17, Problem 84P

Interpretation Introduction

Interpretation:

The product obtained from the Wittig reaction has to be identified.

Concept introduction:

Alkyl bromide reacts with triphenylphosphine to form triphenylphosphonium salt.  The salt is further treated with base to from phosphonium ylide.  Phosphonium ylide reacts with aldehyde or ketone and undergoes $\left[2+2\right]$ cycloaddition mechanism to form alkene as the major product.  Triphenylphosphine oxide is eliminated in the reaction.  This reaction is known as Wittig reaction.

The ${}^1\text{H}$ NMR is used to predict the structure of the organic compounds.  The resonant frequency of a nucleus with respect to a relative compound is called the chemical shift.  Chemical shift is used to identify the nature of the proton.  Spin-spin coupling causes the splitting of signal for each type of nucleus.  The proton splits  the neighbouring proton by the $\left(\text{n}+1\right)$ rule.  The integer, n represesnts the number of protons.  Number of signals gives the chemical environment of the proton.  If protons are chemically equivalent, then one signal is produce in the NMR spectra.