Chapter 6, Problem 1Q

Assign the peaks in the ${}^{\text{1}}\text{H}$

NMR spectrum of eugenol (Fig. 6.23) to specific protons in the molecule. The OH peak is at 5.1 ppm.

Interpretation Introduction

Interpretation:

The peak in ${}^1\text{H}$ spectrum of eugenol should be assigned.

Concept introduction:

NMR is an analytical method that is utilized to identify the structure of a compound. It determines the framework of carbon-hydrogen bonds present in the compound. ${}^1\text{H}$ NMR is used for the analysis of compounds that contains hydrogen atoms.

Number of signals in the ${}^1\text{H}$ NMR of the compound determines the number of different type of hydrogen atoms present in that compound. The splitting of signals is due to protons that are bonded to the adjacent carbon atoms.

The protons that are present in the different chemical environment are known as non-equivalent protons while the protons that are present in same chemical environment are known as equivalent protons.

Answer to Problem 1Q

Eugenol has 12 different hydrogen atoms. The three hydrogen atom present on the aromatic ring show peak around $6.7\text{ppm}$ and the three vinylic hydrogen atom appear around $5-6\text{ppm}$. The three hydrogen atoms of the methoxy group show peak at $3.7\text{ppm}$ and three benzylic hydrogen atoms show peak at $3.3\text{ppm}$.

Explanation of Solution

The structure of eugenol is as follows:

  

Eugenol has 12 different hydrogen atoms. The integration of peaks from right to left is 3:2:2:3:2.

There are two peaks for the three hydrogens around $6.7\text{ppm}$. These peaks are due to the aromatic hydrogen as the aromatic hydrogen are around $7\text{ppm}$.

There are two peaks for four hydrogen atoms around $5-6\text{ppm}$. The one peak is of the hydrogen atom of $-\text{OH}$ group while the one peak is for the three vinylic hydrogen atoms.

There are two peaks for six around $3-4\text{ppm}$. The three hydrogen atoms of the methoxy group are more deshielded as connected to the oxygen atom and therefore show peak at $3.7\text{ppm}$. While the three benzylic hydrogen atoms are less deshielded due to the absence of oxygen atom and show peak at $3.3\text{ppm}$.