Chemistry- Analytical Techniques Flashcards
What are the different analytical Techniques used in chemistry?
- Mass Spectrometry
- Combustion Analysis
- Nuclear Magnetic Resonance
- Infrared Spectroscopy
How does Infrared Spectroscopy work?
Molecules are not Rigid- The bonds within can move and vibrate.
Different functional groups and molecules can absorb IR radiation at different wavelengths, Which makes it possible to identify the functional group within a molecule.
How do you calculate the wavenumber?
Wavenumber = 1 / Wavelength (cm)
What are the different types of NMR?
Carbon NMR
Proton/Hydrogen NMR
What is the fingerprint Region in NMR?
The fingerprint region is to the right of the functional group bonds. It is specific to each molecule.
What do the O-H, C-O & C=O Peaks look like in NMR?
O-H: Strong and broad peak
C-O: Strong but narrow peak
C=O: Strong and narrow peak
What is NMR Spectroscopy?
- Only interested in Carbon 13 Isotopes and Hydrogen atoms to work out Carbon and Hydrogen environments.
Due to the Odd mass number in the atoms, each atom has a nuclear spin.
What is a carbon atom environment?
- The environment around a C^13 Atom.
- In non-polar bonds electrons in the bond shield the nucleus from the external magnetic field and you would have to increase the field to make the nucleus resonate again.
- In polar (with an electronegative atom) the electrons are further away from the carbon^13’s nucleus and so do not affect the magnetic field around it so much.
In NMR what does the number of peaks mean?
The number of peaks is the same as the number of Carbon or hydrogen environments.
What is the standard comparison molecule used to C^13 NMR?
TMS (Tetramethylsilane)
- All carbons are in the same environment
- 4 Carbon nuclei in a similar environment
- C-Si bond is short so carbon nuclei are very well shielded.
Gives a Strong TMS peak at the right hand side of the NMR graph.
TMS is non toxic, inert, easy to removed from sample.
What is Chemical shift?
What type if environment/ bond the C atom is in.
- Horizontal scale is shown as (ppm) is the chemical shift.
- C^13 NMR peaks are less than (to the left) of TMS and are longer than (0-200ppm) the proton NMR (0-12)
What is HNMR or Proton NMR and why does hydrogen produce a peak?
Hydrogen (Proton) Nuclear Magnetic Resonance
Hydrogen atoms are uneven in mass (odd mass number) and therefore will resonate producing a peak.
What is the Integration Trace?
Gives the Number of Hydrogen atoms producing a peak.
Why is TMS used as a standard?
(Tetramethylsilane)
- Hydrogens are all in the same peak/environment
- 12 Hydrogens give a strong TMS peak.
TMS - Non toxic, Inert, Easy to remove from sample.
What is spin-spin splitting (spin-spin coupling)
The applied magnetic field felt by a hydrogen atom is affected by the magnetic field felt by any neighbouring H atoms. (attached to adjacent Carbon Atoms)
Peaks give characteristic splitting patterns which tell you about the neighbouring H atoms.
