L37 - Into To NMR And MRI
No description yet. This curated deck is ready for daily study.
Card preview (24)
What is NMR?
Nuclear magnetic resonance - nucleus of atoms - magnetic fields required - look at solutions of samples
What is MRI?
Magnetic resonance imaging - based on the same effect and quantum mechanical principes - looks at 3D imaging
What does MRI use?
Strong magnetic fields = 3D image
How does MRI work?
Sensing environment of water molecules in body tissues (H nuclei report their local region)
What are the key differences in NMR and MRI?
• MRI - 3D spatial information • NMR - uses solutions for chemical structure
What is NMR used for? (Pharm context)
• analytical techniques for chemical synthesis • used for quantitation and purity • protein and DNA interaction with drugs
What is nuclear spin like?
• spinning charge creates magnetic moment • can line up with/against the field by spinning clockwise/counter clockwise
What is energy like in different alignments of magnetic fields?
• magnetic field a, lower energy than against B • how much lower depends on strength of magnetic field
What are alignment magnetic fields like nuclei that dont have spin?
No difference in energy between alignments, as not magnets
What is the relationship between the magnetic field strength anf difference between energy states?
As field strength increases, energy between a and B increases linearly
What is B0 and v like?
• v directly proportional to B0 • using dif magnets of dif strengths = dif answers • use chemical shifts to fix
What does chemical shift depend on?
Using universal standard
How do you use the chemical shift scale?
• NMR spectrum recorded • frequency of our sample recorded • frequency of standard subtracted, then divided by frequency of standard
What is the eqn for chemical shift?
Shift = (Vsample - Vreference)/ Vreference
What is chemical shift for different protons like?
• appear on different chemical shifts - distinguishable • lies on local magnetic environment of proton
What are chemical shifts for 1H like?
• 10ppm (10-0) • dif types of H - dif shifts • TMS always at 0ppm • positive shifts to the left
When do you move downfield/upfield?
• downfield = less shielding • upfield = more shielding
What is shielding caused by?
• 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
What 3 things affect shielding?
• e- density • electroneg of neighbouring groups • anisotropic induced magnetic effects // aromatic rings
What does electron density do for the nucleus?
Shields nucleus from external field
How do electronegative atoms affect H atoms?
• Pull e- density towards themselves = reduce density around H atom • the more electronegative, the higher ppm, as more shielding
What do double/multiple bonds have large effects on?
• circulating e- produce strong opposing fields = alkenes are downfield • aromatic protons = 8.00-6.5ppm • ring current not symmetrical = above benzene ring upfield
What is the problem with chemical shift data?
Only have range for the shifts (need more knowledge)
What solvents do we use in NMR?
Deutarated solvents = deuterium atoms invisible in proton NMR spectrum