Chapter 13, Problem 13.33SP

An unknown compound has the molecular formula C 9 H 11 B r. Its proton NMR spectrum shows the following absorptions:

singlet, δ 7.1, integral 44 mm

singlet, δ 2.3, integral 130 mm

singlet, δ 2.2, integral 67 mm

Propose a structure for this compound.

Interpretation Introduction

Interpretation:

The structure of the given unknown compound showing the given absorptions in the NMR spectrum is to be proposed.

Concept introduction:

NMR spectroscopy is a technique used to determine the unique structure of the compounds. It identifies the carbon-hydrogen bonding of an organic compound. A hydrogen atom is called as a proton in the NMR spectroscopy.

Answer to Problem 13.33SP

The structure of the given unknown compound showing the given absorptions in the NMR spectrum is given below.

Explanation of Solution

The molecular formula of the compound (${\text{C}}_9{\text{H}}_{11}\text{Br}$).

The double bond equivalent is calculated by the formula,

$\text{DBE}=\left(\begin{array}{l}\text{Number}\text{of}\text{carbon}\text{atoms}-\left(\frac{\text{Number}\text{of}\text{hydrogen}\text{or}\text{halogen}\text{atoms}}{2}\right)\\ +\left(\frac{\text{Number}\text{of}\text{nitrogen}\text{atoms}}{2}\right)+1\end{array}\right)$

Substitute the given values in the above expression.

$\begin{array}{c}\text{DBE}=\left(\begin{array}{l}\text{Number}\text{of}\text{carbon}\text{atoms}-\left(\frac{\text{Number}\text{of}\text{hydrogen}\text{or}\text{halogen}\text{atoms}}{2}\right)\\ +\left(\frac{\text{Number}\text{of}\text{nitrogen}\text{atoms}}{2}\right)+1\end{array}\right)\\ =9-\frac{11}{2}+\frac{1}{2}\\ =4\end{array}$

The DBE value is more than three and one signal present at $\delta 7.1\text{ppm}$ shows that the molecule has one benzene ring.

The other signals present in the NMR spectrum shows that,

$\delta 7.1\text{ppm}$ indicates that the number of protons is 2.

$\delta 2.3\text{ppm}$ indicates that the number of protons is 6.

$\delta 2.2\text{ppm}$ indicates that the number of protons is 3.

From the above data analysis of ${}^{13}\text{C}$ NMR spectrum, the structure of compound which shows the above signals is given as,

Figure 1

Conclusion

The structure of the given unknown compound showing the given absorptions in the NMR spectrum has been rightfully stated.