Q15-54E - Organic Chemistry (Mcmurry)

Question

After the reaction below, the chemical shift of${\mathbf{H}}_{\mathbf{a}}$moves downfield from 6.98 ppm to 7.30 ppm. Explain.

Step-by-Step Solution

Answer

In the case of the product formed the protons give a higher value of around 7.30 ppm as the protons are now in the deshielding zone of the new p electron cloud formed.

Step 1: Chemical shift

In NMR spectroscopy the chemical shift is the resonating frequency of the atomic nucleus compared to the standard chemical shift in a magnetic field.

Step 2: Chemical shift of the reaction

The reaction taking place is as follows:

In the starting compound, the protons marked to give a peak around due to the presence of electron-donating methoxy groups.

In the case of the product formed the protons give a higher value of around 7.30 ppm as the protons are now in the deshielding zone of the new p electron cloud formed.