Nuclear Magnetic Resonance (Nmr) Spectroscopy

Front 1

NMR

Back 1

• Technique for determining the structure of organic compounds
• Complementary to X-ray crystallography
• Not destructive like Mass spec
• Requires a larger sample size than MS

Front 2

NMR definition

Back 2

• Technique for determining the structure of organic compounds
• Measures the nucleus
• Can study physical, chemical, and biological properties of matter

Front 3

NMR Principle

Back 3

• Many nuclei are charged and spin and can absorb energy to a higher energy
• Energy transfer takes place at a wavelength equal to a radio frequencies
• when spin returns to the base level and emitted at the same frequency
• The signal is transferred and measured

Front 4

Resonance

Back 4

• The nucleus of many atoms act like magnets
• When put in a magnet N and S match up
• the absorb some energy and behave in a way described as wobble or flip or spin

Front 5

NMR picture

Back 5

• 3D picture of a molecule produce a profile or spectrum
• When exposed to magnetic energy will produce a spectrum
• Show the relationship between different atoms
• Used to study DNA, Carbs, DNA, etc

Front 6

Spin

Back 6

• Most atoms will resonate or absorb energy at a specific radio wave frequency (RF) when placed in a strong magnetic field
  
• Nucleus don't have a spin (proton and neutrons cancel each other out)
• Spins can be positive or negative

Front 7

What is spin?

Back 7

• Comes in multiples of 1/2 and can be + or -
• Protons, electrons, and neutrons possess spin
• unpaired e, p, and n posses a 1/2 spin
• Unpaired nuclear spins are important

Front 8

Deuterium atom

Back 8

• 2H
• One unpaired electrons, one unpaired proton, and one unpaired neutron
• The total spin: 1/2
• Nuclear spin=1

Front 9

If the number of neutrons and the number of protons are both even

Back 9

the nucleus has no spin

Front 10

If the number of neutrons plus the number of protons are odd

Back 10

then the nucleus is has half an integer spin

1/2, 3/2, 5/2

Front 11

If the number of neutrons and the number of protons are both odd then the nucleus has

Back 11

an integer spin: 1, 2, 3

Front 12

The energy with the spin depends on how it reacts when

Back 12

it is exposed to another magnetic field

Front 13

The energy required to flip depends on

Back 13

the strength of the applied magnetic field. The energy needed is usually very small

Front 14

Turning off the radio waves

Back 14

the atoms will relax back into their initial lower energy

this lower energy will produce a measurable quantity of radio frequency waves that can be measured

Front 15

The signal in NMR results from the

Back 15

difference between the energy absorbed by the spins which make a transition form the lower energy state to the higher, the energy emitted by the spins which simultaneously make a transition from the higher energy state to the lower energy state

The signal is proportional to the populatino difference between the two states

Front 16

NMR signal

Back 16

Difference between the energy absorbed by the spins which makes a transition from lower to higher energy

The energy emitted by the spins from higher to lower energy

Front 17

Continous Wave

Back 17

constant frequency

operates with a pulse technique

all resonance frequencies are produced

the strength of the external magnetic field are varied

Front 18

Fourier Transform

Back 18

E=hv

the frequency of the photon in the RF range

60-800MHz for hydrogen nuclei

MRI is between 15-80

Front 19

NMR magnet

Back 19

• The length of the magnet is typically several meters
  
• wound into a solenoid coil
  
• temp 4.2K (emersed in liquid helium)
• kept in dewar surrounded by liquid nitrogen

Front 20

Chemical shift

Back 20

• pattern of differing precession frequencies
• How far down from the TMS the side changes cause the frequency to change
• Frequency is related to the chemical structure

Front 21

Chemical shift Theory

Back 21

• Each nucleus is surrounded by a cloud of electrons
• Electrons generate a magnetic field they add/subtract to external field
• these are noticed by the nucleus and the resonance freq are altered
• Each molecule has a unique NMR specturm

Front 22

What causes chemical shift

Back 22

• small magnetic field opposed to the applied magnetic field
  
• the nucleus feels a magnetic field that is less than the field that is actually applied
• Known as sheilding

Front 23

J-coupling

Back 23

• interaction of spins within the same molecule
  
• those physically close to each other exhibit stronger coupling than those further away
  
• Observe split lines on absorption spectrum
• Only occurs between non-equivalent nuclei

Front 24

MRI

Back 24

• Sends radio waves through the patients body
• Affects the body's atoms, forcing the nuclei into a different position
• As they move back they send out a radio wave
• The scanner picks up the signal and the computer turns them into a picture

Front 25

Becuase of the body's high water content the nucleus of

Back 25

the hydrogen atom is often used to create the MRI scan