Chapter 15, Problem 79IP

Interpretation Introduction

Interpretation: The molecular formula and the structure of an unknown compound to be predicted using spectrum details.

Concept Introduction:

Molecular formula: It represents the types of atoms with their total number present in a given molecule.

Mass spectroscopy: It is a form of spectroscopic technique which is used for the elucidation of the molecular formula and molecular weight of the compound, depending upon the mass of the molecule.

Molecular ion peak ${\text{(M)}}^{\text{+}·}$: It is defined as the heaviest peak in the IR spectrum of the molecule which represents the largest molecular ion in the given molecule with greater m/z value.

The ${\text{(M+1)}}^{\text{+}·}$ peak: It denotes the peak that arises next to molecular ion peak in the mass spectrum. The peak arises due to the presence of the isotope of carbon $\left({}^{\text{13}}\text{C}\right).$

The ${\text{(M+1)}}^{\text{+}·}$ peak in mass spectroscopy is used to explain the number of carbon atoms present in a molecule depending on the abundance of ${\text{(M+1)}}^{\text{+}·}$ peak.

${}^{\text{1}}\text{H}\text{NMR}$: The ${}^{\text{1}}\text{H}\text{NMR}$ spectrum gives information on the different electronic environment of protons. The number of signal (proton types) generated in ${}^{\text{1}}\text{H}\text{NMR}$ are predicted by performing symmetry operations (rotation or reflection symmetry).

The ${}^{\text{13}}\text{C}\text{NMR}$ spectrum gives information on the different electronic environments of carbon. As like ${}^{\text{1}}\text{H}\text{NMR}$, the number of signals generated in ${}^{\text{13}}\text{C}\text{NMR}$ are predicted by performing symmetry operations (rotation or reflection symmetry). Only chemical shift values are reported in the spectrum but not the multiplicity and integration values because the coupling between two neighboring ${}^{\text{13}}\text{C}{-}^{\text{13}}\text{C}$ nuclei are weakly involved due to the low abundance of ${}^{\text{13}}\text{C}$ isotopes of carbon atom.

HDI Calculation:

$\begin{array}{l}\text{HDI=}\frac{\text{2(C)+2+N-H-X}}{\text{2}}\\ \text{where}\\ \text{C}\text{represent}\text{the}\text{number}\text{of}\text{carbon}\\ \text{N}\text{represent}\text{the}\text{number}\text{of}\text{nitrogen}\\ \text{H}\text{represent}\text{the}\text{number}\text{of}\text{hydrogen}\\ \text{X}\text{represent}\text{the}\text{number}\text{of}\text{halogen}\text{.}\end{array}$