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  5. A Level Chemistry
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  7. Unit 3.3.15 - Nuclear magnetic resonance spectroscopy

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Summary NMR Revision Notes

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Here are my revision notes for the NMR section of the course. Feel free to check out my other computer typed notes for parts of the 2nd year course on here. I also have hand written notes of matching quality for pretty much the rest of the course (1st and 2nd year) if you're interested. Email...

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  • Chapter 32
  • August 5, 2021
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  • 2020/2021
  • Summary

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1.1. NMR Spectroscopy 2.1. Proton NMR
2.2. Integration Trace
Technique to find structures of complex molecules Examining Hydrogen nucleus
Magnetic field is applied to sample Basically, all H atoms are H1 so much easier Area of each peaks is related to
Sample is dissolved in a solvent and placed in machine Same principal of different environment means a different Integration
Trace number of H atoms producing it
Solvent could be CCl4, CDCl3, D2O, C6D6 chemical shift For methanol, CH3 peak is 3x area of
Sample is also surrounded by radio waves and radio receiver More electrons surrounding H nucleus means better OH peak
Generates energy change in nuclei of atoms in sample shielding Instrument used produces a line
Electromagnetic energy is emitted, interpreted on computer Chemical shift values are smaller (0 – 10 ppm) called integration trace
Relative heights give
The further away a H atom is from an electronegative relative ratio of each
atoms, the smaller its chemical shift environment
1.2. Carbon-13 NMR NMR Spectrum of Methanol
Areas under the peak are proportional to number of H
Used to detect carbon atoms in a sample and determine the sample’s atoms in each environment
structure
Not all carbon-13 atoms resonate the same ways 2.3. TMS
Carbon in different functional groups resonate
differently Chemical shift values are measured by referring to the standard value, given
Because all nuclei are shielded from external forces by electrons by TMS
Nuclei with more electrons are better shielded Number of environments is Chemical shift of TMS is 0 by definition
The greater electron density means the smaller the magnetic field felt by the number of signals TMS is a liquid and can be added to samples before spectra are run, and a
the nucleus and lower frequency it resonates at peak at 0ppm is seen
Carbon-13 has spin – odd number of electrons, which spin different ways TMS is used to help calibrate the spectra

Chemical shift values for Properties: only gives one signal
C-NMR and H-NMR are Organic Chemistry: non-toxic
1.3. Chemical Shift inert
given in data booklet Structure Determination (NMR)
low bpt (26 degrees), so can be easily removed
Measured in parts per million (ppm) from defined 0 based on TMS
(Tetramethylsilane)
Chemical shift is related to difference in frequency between
resonating nucleus and TMS 2.4. Interpreting Spectra
Carbon-13 chemical shift is between 0 – 200ppm
Carbon atoms in different environments give different chemical shift Spin Spin Coupling: NMR peaks being split into particular patterns
values Happens because applied magnetic field felt by H-atoms is
based on electronegativity, atoms the C is bonded to affected by magnetic field of H-atoms on neighbouring C
atoms
One of the C’s in this number of lines signal is split into gives info about nearby H-
substance is bonded to an 2.5. MRI atoms
Oxygen atom which is
signal for H-atoms is only split by inequivalent H’s (different
more electronegative
than C and H, so draws Magnetic Resonance Imaging number of H-atoms on adjacent atom
the electron density and Used to investigate human body uses the “n+1” rule
creates a different Signal came from protons in water molecules in
environment than the C body N+1 Rule: Number of lines = number of inequivalent H atoms + 1
bonded to 3 H’s
Water in different parts of the body gives 1 H atom on adjacent C will split into 2 peaks (doublet)
different signals 2 H atoms on adjacent C will split into 3 peaks (triplet)
Patient passes through scanner, and 3D image 3 H atoms on adjacent C will split into 4 peaks (quartet)
Height of peaks isn’t important
The position is!!! constructed

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