Chapter 14, Problem 32P

Interpretation Introduction

Interpretation:

Electron delocalization in cyclooctatetraene based on the location of signal in $\text{H}\text{ NMR}$ is to be explained.

Concept introduction:

Nuclear Magnetic Resonance (NMR) is one of the most capable analytical techniques used for determining the functional groups and how the atoms are structured and arranged in a molecule.

Few elements, such as ${}^{13}{\text{C and }}^1\text{H}$, have nuclei behaving as magnets about an axis. These elements are placed in magnetic field irradiated with electromagnetic energy of specific frequency and the nuclei tend to absorb energy via magnetic resonance. There is this graph that shows energy absorption frequencies and intensities of a sample kept in the magnetic field called nuclear magnetic resonance (NMR).

In $\text{NMR}$ spectroscopy, the proton nuclear magnetic resonance ${(}^{\text{1}}\text{H}\text{NMR)}$ is used to find out the structure of molecules with the help of ${}^{\text{1}}\text{H}$ atom within the molecules.

Induced magnetic field consists of electricity generated from movement in a magnetic field.

The position of a signal on x-axis in the $\text{NMR}$ spectrum depicts the chemical shift expressed in $\delta$ or $\text{ppm}$.

The number of signals in $\text{H}\text{ NMR}$ spectrum represents the number of different chemical environments for the protons.

The area covered by the signal is proportional to the number of equivalent protons causing the signal.

The hydrogen atoms on adjacent carbon atoms split the signal into two or more peaks. One, two or three hydrogen atoms split the signal into two, three or four peaks described as doublet, triplet or quartet respectively.

A decrease in the electron density around a proton deshields the signal downfield at a larger value of chemical shift.

An increase in electron density shields the signal upfield at a lower value of chemical shift.

${}^{13}\text{C}$ NMRis only used in the observation of isotopes of carbon atoms.

The number of signals in NMR spectra shows the number of different chemical environments in a molecule.

Aromatic protons give signal downfield between $\delta 6$ and $8.5$.

Alkene protons give signal upfield between $\delta 4.5$ and $6.5$.Cyclooctatetraene contains four conjugated double bonds.