introduction to nmr
TRANSCRIPT
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1
Nuclear Magnetic Resonance Spectroscopy
SAHANA
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2Gorter- First to use the terminology NMR
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3NMR-A True “Noble” Analysis
Magnetic moment of the proton
Resonance method for recording the
magnetic properties of atomic nuclei
Nuclear magnetic precision
measurements and discoveries in
connection therewith
High resolution nuclear magnetic resonance (NMR)
spectroscopy
1991195219441943
Richard R. Ernst
Chemistry
Felix Bloch Edward M. Purcell
Physics
Isidor I. Rabi
Physics
Otto Stern
Physics
Nominated 82 times for Noble prize
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4NMR-A True “Noble” AnalysisDevelopment of nuclear magnetic
resonance spectroscopy for determining the three-
dimensional structure of biological macromolecules in
solution
Magnetic resonance imaging
2002 2003
Kurt Wüthrich
Chemistry Medicine
Paul C. LauterburPeter Mansfield
First NMR Structure- BPTI
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5Why NMR? [Applications]
• Identification • Analysis of
material
• Protein Structure• Kinetics
• Condensed Matter Physics
• MRI
Medical Physics
ChemistryBiology
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6Magnetic Moment of Proton
Otto Stern
Walter Gerlach
Stern- Gerlach Experiment
7Magnetic Moment of Proton Spinning Proton (Charged)- Creates
Magnetic Field. Hence, they are “Tiny Bar Magnets” External Magnetic field (Ho/Bo), they
align against or toward this applied field.
is Magnetic Moment is gyromagnetic ratio. I is spin quantum number. h is planks constant
I=1/2 : charged, spinning spherical bodies and give the best resolved spectra
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8Magnetic Moment of Proton Who can “Spin”? P31, F19, N15, C13, H1
Because, Z and N should be odd in number
Z = P + NNucleons
Protons
Neutrons
Low Energy, NS High Energy, SN
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9Energy Gap and its importance
∆𝐸=h𝑓=𝜇𝐼 𝐻0
Energy difference corresponds to a frequency
More the magnetic field, more the energy gap
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10Resonance of the Proton Axis of the spinning nuclei is not fixed in the magnetic field. Hence, they Precess/ Wobble. LARMOUR FREQUENCY: = Bo
2 (Frequency) Gyromagnetic Ratio Bo Magnetic FieldIsidor I. Rabi
Radiowaves at Larmour Frequency to “Tiny Bar Magnets”
∆𝐸=h𝑓=𝜇𝐼 𝐻0
Nucleus spin is in Resonance with the applied magnetic field, thus Nuclear Magnetic Resonance
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11Thus NMR is..
External MagneticField Bo/Ho
Radio Waves
Nucleus Align in resonance with the applied Magnetic field and radio waves
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12The Relaxation Effect
Highly Unstable State
Stable State
External Magnetic Field Bo/Ho
Emits Radiofrequency
Measured as Spectrum
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13Relaxation- Measure
Felix Bloch
Edward M. Purcell
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14Relaxation- Measure
Richard R. Ernst
High resolution nuclear magnetic resonance (NMR) spectroscopy in a matter of seconds
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15Fourier Transform- What it transforms?
a) Single frequency Sine Waves
b) Single frequency FID
c) Three sine wave combination
Converts Time domain into Frequency Domain
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16Instrumentation
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17Working- A Closer Look
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18Instrumentation- Sample Holder
Material: Borosilicate GlassDimensions: 1. 3mm – 10mm in diameter2. 7-8 inches in heightSpecifications:3. Concentricity
Difference between two radial centers using the outer and inner tube's circumference as reference points.
Larger difference Non-homogeneity of magnetic field
4. Camber Measurement of the degree of curvature of the
tube Larger value Causes wobbling of the tube while
spinning
Felix Bloch
Spinner
Sample tube
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19
Minimum Concentration: 5mg/mL Solvents : CCl4, CDCl3, D2O, C6D6
Why deuterated solvents? To avoid swamping of the solvent
signal To stabilize the magnetic field To accurately define 0ppm
Cleaning of tubes: Piranhana Solution/ Aqua Regia
Instrumentation- Sample Preparation
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20A typical NMR Spectrum
Acidic Sophorolipid
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21NMR Spectrum- Chemical Shift Chemical Shift: Difference in parts per million between the resonance
frequency of the observed proton and TMS (Trimethyl silane) hydrogens. TMS ppm is set to 0.
Shielding/ Deshielding of protons
Factors affecting the Chemical Shift:1. Electronegativity2. Magnetic Anisotrophy3. Hydrogen Bonding
HighElectron density
LowElectron density
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22NMR Spectrum- Chemical Shift
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23NMR Spectrum- Intensity
Intensity No. of Absorbing Protons
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24NMR Spectrum- Spin-Spin Coupling
Signals for different protons are split into more than onepeak termed as Spin-Spin Coupling or Splitting.
Spin-spin splitting occurs only between nonequivalent protons on the same carbon or adjacent carbons.
The frequency difference, measured in Hz between two peaks of the doublet is called the coupling constant, J
Multiplicity Rule n+1 rule, where n is the number of
neighboring spin-coupled nuclei with the same (or very similar) Js
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25NMR Spectrum- Interpretation Number of signals: Indicates how many different kinds
of protons are present Position of signals: Indicates Magnetic environment of
the signal Relative Intensity: Proportional to number of protons
present Splitting: Indicates number of splitting Nuclei [Usually
Protons]
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26Difference between Proton NMR and C13 NMR
Proton NMR 13C NMR
1. It is study of spin changes of proton nuclei.
1. It is study of spin changes of carbon nuclei.
2. Chemical shift range is 0-14 ppm.
2. Chemical shift range is 0-240 ppm.
3. Continuous wave method 3. Fourier transform Method4.slow process 4.Very fast process.
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27Signature Ranges
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28Types of NMR
1D NMR 2D NMR: Data plotted in a space
defined by two frequency axes rather than one representing the chemical shift
Types of 2DNMR: Correlation spectroscopy (COSY) J-spectroscopy exchange
spectroscopy (EXSY) Nuclear Overhauser
effect spectroscopy (NOESY)
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29Take Away Messages05/01/2023
Without Passion, Life
Becomes Senseless
Free imagination is
the inestimable
prerogative of
youth and it must
be cherished and
guarded as a
treasure
I think physicists are the Peter Pans
of the human race. They never grow up and they keep their curiosity.
You could write the
entire history of
science in the last
50 years in terms of
papers rejected by
Science or NatureShall we do it?
Well, then let's go, we shall do it!