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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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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!