Chapter 17, Problem 45P

Interpretation Introduction

Interpretation:

The structure of phenacetin and phenetidine from the given data are to be determined.

Concept introduction:

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.

Infrared absorption bands indicate the functional groups present in a compound. For example, carbonyl group shows a band from $1600\text{ to }1750{\text{ cm}}^{\text{-1}}$, hydroxyl group shows a band from $\text{3400 to 35}50{\text{ cm}}^{\text{-1}}$. So, if a compound shows band in the carbonyl range only, it is an aldehyde or ketone; if in the region of hydroxyl, it is alcohol or phenol; if two bands are observed, one in each region, it is a carboxylic acid.

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.

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

NMR data indicates the number and type of protons or carbons present in a compound based on a number of signals obtained in ${}^1\text{H}$ NMR or ${}^{13}\text{C}$ NMR respectively. ${}^1\text{H}$ NMR signals are often in multiplicity such as doublet, triplets that indicates the number of protons present on the carbons adjacent to that proton. Protons of aromatic ring shows signal from $6.5–7.5\text{ ppm}$, those of alkyl group from $0.5\text{ to }1.5\text{ ppm}$ while alkyl groups adjacent to a carbonyl group or oxygen atom show signals from $2.0\text{ to }3.0\text{ ppm}$. Alcohol group shows a signal at $2.0\text{ to }3.0\text{ ppm}$ but is always a singlet.