Question

What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula CoH1nO2? Relative integration is shown. 10 PPM

Answer 1

The Double bond equivalence count says that ,

$\dpi{120} \bg_white DBE=9+1-\frac{10}{2}=5$

That is one phenyl (DBE=4) ring with one extra double bond .

Thus , 2nd structure is not possible .

Now , 4 types of different protons are there ( as 4 different peaks) .

5 protons in the scale 7-8 ppm refers aromatic protons .

The 3rd structure has 4 aromatic protons . So , it is not possible .

There are two different peaks with 2 protons each at ppm (2-3) . Thus , last structure cannot be true as it has two different proton types having 1 and 3 protons .

The ppm>12 is possible only for carboxylic acid proton and not for aldehyde proton ( around 9 ppm ) .

So , the forth structure is the correct structure .

729 7.40 H -OH 21 HH 7.27H H.251 251 PPM