Chapter 16, Problem 16.83P

Interpretation Introduction

Interpretation:

The structure of the compound of the formula ${\text{C}}_{\text{9}}{\text{H}}_8\text{O}$ is to be determined using its IR, ${}^{\text{1}}\text{H}$ NMR, and ${}^{\text{13}}\text{C}$ NMR spectra.

Concept introduction:

The structure of a compound can be determined from the IR and NMR spectra.

The IR spectrum of a molecule consists of several absorption peaks/bands. These bands, particularly those above about 1200 ${\text{cm}}^{-1}$, are characteristic of different functional groups and the nature of $\text{C}-\text{H}$ bonds (hybridization of carbon).

The ${}^{\text{1}}\text{H}$ NMR spectrum provides information about the types of structurally distinct hydrogens and the number and types of coupled hydrogens. This helps identify fragments of the molecule.

The ${}^{\text{13}}\text{C}$ NMR spectrum provides information about the structurally distinct types of carbon atoms in the compound.

The formula of the compound, if known, can provide information about the unsaturation, number of double or triple bonds, and rings in the structure. This is known as the Index of Hydrogen Deficiency (IHD), and for a molecule containing only C, H, and O, it is calculated as ${\text{IHD = (C}}_{\text{n}}{\text{H}}_{\text{2n+2}}{\text{ - C}}_{\text{n}}{\text{H}}_{\text{x}}\text{)/2}$.

Using this information, the possible ways in which the fragments and functional groups are connected can be determined, leading to the probable structure of the molecule.