Spectroscopy Introduction

In our next piece of work, we will use three type of spectra to learn about some organic compounds. The spectra are:

1. Infrared (IR)
2. Mass
3. ¹³C-NMR

In our first lesson, we simply learned about these three spectra and what they tell us about an unknown sample. In our assessment, we need to use evidence from all three spectra to decide what an unknown organic compound is.

IR SPECTROSCOPY

SOURCE: https://www.compoundchem.com/2015/02/05/irspectroscopy/

Organic compounds have characteristic functional groups. Each functional group has a unique "fingerprint" in an IR spectrum.

SOURCE: https://www.compoundchem.com/2020/02/21/functional-groups/

As we learn about each functional group, we will also explore their characteristic IR spectra.

SOURCE: https://www.compoundchem.com/2015/02/05/irspectroscopy/

MASS SPECTROMETRY

SOURCE: https://www.compoundchem.com/2015/05/07/mass-spectrometry/

"Mass Spec" gives us some very useful information to differentiate between compounds that contain the same (or similar) functional groups. Mass Spec smashes compounds into unique fragments. Working out how these fragments go together allows us to eliminate possible structures and confirm our chosen structure.

SOURCE: https://www.compoundchem.com/2015/05/07/mass-spectrometry/

¹³C-NUCLEAR MAGNETIC RESONANCE

SOURCE: https://en.wikipedia.org/wiki/File:13C_NMR_ethanol.GIF

¹³C-NMR will be called "NMR" in this unit. It is different to ¹H-NMR which is used much more commonly in industry and analytical chemistry, but ¹³C-NMR is better for learning about coming to conclusions from the graphs produced by NMR analysis.

We use ¹³C-NMR to differentiate between isomers (different structures with the same molecular formula) and other compounds with very similar IR spectra and Mass Spec fragments. This is done in two ways:

1. Number of unique carbon environments
2. Chemical shift caused by different functional groups bound to carbon atoms

SOURCE: https://www.compoundchem.com/2015/04/07/carbon-13-nmr/