Interpret infrared spectra, mass spectra and proton NMR spectra to determine the structure of organic molecules.

What this dot point is asking

You must interpret each spectrum and combine the evidence to deduce a structure.

Infrared spectroscopy: functional groups

IR radiation makes bonds vibrate. Each type of bond absorbs at a characteristic wavenumber (cm$^{-1}$), so an IR spectrum reveals which functional groups are present. Diagnostic absorptions you should recognise:

Bond	Approx. wavenumber / cm$^{-1}$	Found in
O-H (broad)	$3200$-$3550$	alcohols
O-H (very broad)	$2500$-$3300$	carboxylic acids
C=O	$1700$-$1750$	aldehydes, ketones, acids, esters
C-H	$\sim 2850$-$3000$	alkanes

Mass spectrometry: molar mass and fragments

A mass spectrometer ionises molecules and separates the ions by mass-to-charge ratio ($m/z$).

• The molecular ion peak (M$^+$) - the peak at the highest $m/z$ - gives the relative molecular mass of the compound.
• Fragment peaks at lower $m/z$ come from the molecular ion breaking apart; the mass differences identify groups lost (e.g. a loss of $15$ suggests a $\text{CH}_3$ group; a loss of $29$ suggests CHO or $\text{C}_2\text{H}_5$).

Proton ($^1$H) NMR: hydrogen environments

$^1$H NMR detects hydrogen atoms in different chemical environments:

• the number of peaks (signals) equals the number of different hydrogen environments;
• the chemical shift ($\delta$, ppm) indicates the type of environment;
• the relative area (integration) of each peak is proportional to the number of hydrogens in that environment.