L37 - Into To NMR And MRI

Question 1

What is NMR?

Answer 1

Nuclear magnetic resonance
- nucleus of atoms
- magnetic fields required
- look at solutions of samples

Question 2

What is MRI?

Answer 2

Magnetic resonance imaging
- based on the same effect and quantum mechanical principes
- looks at 3D imaging

Question 3

What does MRI use?

Answer 3

Strong magnetic fields = 3D image

Question 4

How does MRI work?

Answer 4

Sensing environment of water molecules in body tissues
(H nuclei report their local region)

Question 5

What are the key differences in NMR and MRI?

Answer 5

• MRI - 3D spatial information
• NMR - uses solutions for chemical structure

Question 6

What is NMR used for? (Pharm context)

Answer 6

• analytical techniques for chemical synthesis
• used for quantitation and purity
• protein and DNA interaction with drugs

Question 7

What is nuclear spin like?

Answer 7

• spinning charge creates magnetic moment
• can line up with/against the field by spinning clockwise/counter clockwise

Question 8

What is energy like in different alignments of magnetic fields?

Answer 8

• magnetic field a, lower energy than against B
• how much lower depends on strength of magnetic field

Question 9

What are alignment magnetic fields like nuclei that dont have spin?

Answer 9

No difference in energy between alignments, as not magnets

Question 10

What is the relationship between the magnetic field strength anf difference between energy states?

Answer 10

As field strength increases, energy between a and B increases linearly

Question 11

What is B0 and v like?

Answer 11

• v directly proportional to B0
• using dif magnets of dif strengths = dif answers
• use chemical shifts to fix

Question 12

What does chemical shift depend on?

Answer 12

Using universal standard

Question 13

How do you use the chemical shift scale?

Answer 13

• NMR spectrum recorded
• frequency of our sample recorded
• frequency of standard subtracted, then divided by frequency of standard

Question 14

What is the eqn for chemical shift?

Answer 14

Shift = (Vsample - Vreference)/ Vreference

Question 15

What is chemical shift for different protons like?

Answer 15

• appear on different chemical shifts - distinguishable
• lies on local magnetic environment of proton

Question 16

What are chemical shifts for 1H like?

Answer 16

• 10ppm (10-0)
• dif types of H - dif shifts
• TMS always at 0ppm
• positive shifts to the left

Question 17

When do you move downfield/upfield?

Answer 17

• downfield = less shielding
• upfield = more shielding

Question 18

What is shielding caused by?

Answer 18

• e- near nucleus move constantly
• e- create locally induced magnetic field that acts opposite to main field (B0)
  = reduces total magnetic field experience by nucleus

Question 19

What 3 things affect shielding?

Answer 19

• e- density
• electroneg of neighbouring groups
• anisotropic induced magnetic effects // aromatic rings

Question 20

What does electron density do for the nucleus?

Answer 20

Shields nucleus from external field

Question 21

How do electronegative atoms affect H atoms?

Answer 21

• Pull e- density towards themselves = reduce density around H atom
• the more electronegative, the higher ppm, as more shielding

Question 22

What do double/multiple bonds have large effects on?

Answer 22

• circulating e- produce strong opposing fields = alkenes are downfield
• aromatic protons = 8.00-6.5ppm
• ring current not symmetrical = above benzene ring upfield

Question 23

What is the problem with chemical shift data?

Answer 23

Only have range for the shifts (need more knowledge)

Question 24

What solvents do we use in NMR?

Answer 24

Deutarated solvents = deuterium atoms invisible in proton NMR spectrum

Question 25

What is the D2O shake?

Answer 25

• D2O added to a sample dissolved in another solvent
• deuterium atom from solvent exchanges with proton = vanishes from spectrum
• allows us to identigy exchangeable atom = simplifies spectra