Nuclear Magnetic Resonance Spectroscopy

Presented by: Reitumetse Nkhahle

Nuclear Magnetic Resonance (NMR) Spectroscopy

• Nuclear Magnetic Resonance – Absorption and re-emission of electromagnetic

radiation.

• Spectroscopy – Technique used to measure light scattered,

absorbed or emitted by matter.

Principles of NMR • Subatomic particles have a spin. • Nuclei with a ½ spin behave like a magnet: Figure 1: Nuclei interaction with external magnetic field.

• Examples of elements with nuclei that have a spin of ½:

– 13C – 1H – 15N

Image sourced from: http://www.chem.ucla.edu/~harding/notes/notes_14C_nmr02.pdf

The NMR Spectrometer

• Continuous wave spectrometer – Outdated – Solid-state NMR applications

• Fourier transform spectrometer – Signal is measured in time (s) – Fourier transform converts signal measured in

time-domain to a frequency vs intensity plot.

The Fourier Transform Spectrometer

Figure 2: Illustration of an FT-NMR spectrometer.

Image sourced from: http://chem4823.usask.ca/nmr/magnet.html.

Experimental factors

• Tuning • Shimming • Locking • Temperature • Sample preparation

Detection of the NMR signal

Figure 3: Image illustrating the production of NMR spectra.

Images sourced from: http://image.slidesharecdn.com/bt63116nmr1-140325231614-phpapp02/95/bt63116nmr1-16-638.jpg?cb=1395789681 and http://slideplayer.hu/slide/2028189/.

Types of NMR spectra 1H NMR 13C NMR

Figure 4: 1-dimensional NMR spectra of carbon-13 and hydrogen.

Images sourced from: http://www.odinity.com/wp-content/uploads/2014/01/NMR_benzene.png and http://www.chemguide.co.uk/analysis/nmr/c13acrylate.gif.

Types of NMR spectra Homonuclear correlation spectroscopy (COSY)

Heteronuclear multiple-bond correlation spectroscopy (HMBC)

Figure 5: Examples of 2-dimensional NMR spectra. Images sourced from: http://img.dxycdn.com/upload/2005/09/29/24419253.gif and http://131.104.156.23/Lectures/CHEM_207/CHM_207_Pictures_NMR/NMR_2D_COSY_color.gif.

Interpreting NMR spectra – chemical shifts

Figure 6: Chemical shifts for proton and carbon-13 NMR.

Image source from: http://image.slidesharecdn.com/nmr-140924032539-phpapp02/95/nmr-spectroscopy-47-638.jpg?cb=1411529227.

Advantages

• Provides both qualitative and quantitative information.

• Samples can be recovered. • A small quantity of material is required for

analysis. • Preparation of sample is easy.

Disadvantages

• Poor sensitivity. • Requires special infrastructure and training. • Spectra takes a long time to interpret. • Potential fire hazard. • Very expensive.

Applications

• Compound identification and confirmation. • Chemical composition determination. • Molecular conformation determination.

• Raw materials fingerprinting.

• Quality assurance and control.

Thank you.