Chapter 14, Problem 38P

Interpretation Introduction

Interpretation:

The number of signals in $\text{H}\text{ NMR}$ and characteristic peaks in $\text{IR}$ spectrum are to be predicted for caffeine.

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.

Any signal’s position on the X-axis in the $\text{NMR}$ spectrum is the chemical shift expressed in $\delta$ or ppm.

The number of signals in $\text{H}\text{ NMR}$ spectrum tells about 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 atom on adjacent carbon atoms splits the peak into two or more peaks. One, two, and three hydrogen atoms split the peak into two, three and four peaks, which further, is referred to as doublet, triplet or quartet.

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

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

Infrared spectroscopy is a simple, instrumental technique, which helps to determine the presence of various functional groups.

It depends on the interactions of atoms or molecules with the electromagnetic radiation.

Infrared spectroscopy is most commonly used in the identification of the structure of the compound.

Infrared spectroscopy is the examination of the infrared light interacting with a molecule. The examination can be done in three ways, that is, by measuring absorption, emission, and reflection, and it can also measure the vibration of atoms.

$\text{IR}$ Spectrum shows absorptions due to stretching and bending vibrations in a molecule. Benzene compounds show characteristic $\text{C-H}$ stretching and bending peaks. Functional groups like carbonyl and amino group, further, show characteristic peaks in the IR spectrum.