Further organic chemistry: Spectroscopy & Chromatography -4
- Created by: Shannon
- Created on: 07-04-15 11:23
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- Spectroscopy and Chromatography
- Different types of radiation on molecules
- UV
- Used to initiate reactions
- Causes covalent bonds to break homolytically, resulting in free radicals
- Radio waves
- Used in nmr
- Affects the spin of hydrogen nuclei in a strong magnetic field
- Microwaves
- Used for heating
- Cause molecules with polar bonds to rotate faster
- Infrared
- Used in analysis
- Causes the bending and stretching of bonds
- UV
- NMR spectroscopy
- Identifies the structure of molecules using radio waves
- How many hydrogens there are and how they're arranged
- Hydrogen nuclei (protons) are spinning, this means that in the nuclei there is a weak magnetic field
- NMR looks at how this magnetic field reacts when it is placed in a larger external magnetic field
- Spin states are degenerate
- When in an external magnetic field, protons align themselves either with the direction of the fields or opposing it
- Aligned protons are at lower energy than the opposing protons
- If they absorb radio waves they can be promoted to the higher energy level
- Energy emitted when returning to group state
- If they absorb radio waves they can be promoted to the higher energy level
- Opposing protons, at higher energy, can emit radio waves and 'flip' to the lower energy level
- Spin states non-degenerate
- Aligned protons are at lower energy than the opposing protons
- Protons in different chemical environments absorb different amounts of energy
- The environment is dependent on the groups it is attached to
- If protons are in the same chemical environments, they are referred to as being 'equivalent'
- Signals on a NMR spectrum are due to one or more protons in a particular proton environment
- Signals can be split, these are dependent on the number of protons on the neighbouring carbon atom
- Add 1 to the number of Hs on adjacent atoms
- Splitting only seen on a high resolution nmr
- Signals can be split, these are dependent on the number of protons on the neighbouring carbon atom
- Electrons provide shielding
- Deshielded end of spectrum (left) - stripped electrons
- Shielded end of spectrum (right) - electron density not stripped
- The environment is dependent on the groups it is attached to
- Identifies the structure of molecules using radio waves
- Infrared
- Infrared spectroscopy can be used to follow a reaction
- Changing functional groups
- Infrared spectroscopy can be used to follow a reaction
- Chromatography
- Gas chromatography
- Mobile phase = a gas (normally inert)
- Stationary phase = solid - silicia on outside of column
- Low affinity for stationary phase are eluted first
- HPLC
- Mobile phase = a solvent
- Stationary phase = solid - silicia on outside of column
- Reverse phase - uses polar solvents and a non-polar stationary phases
- Normal phase - uses non-polar solvent and a polar stationary phase
- The separation of mixtures
- Gas chromatography
- Mass spec
- Has characteristic fragment patterns, e.g CH3 = peak @15
- Molecular ion peak = Mr
- Different types of radiation on molecules
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