NMR

Question 1

Nuclear spins

Answer 1

Nuclei of atoms act as tiny magnets

Question 2

Spins in magnetic field

Answer 2

strong magnetic field applied - nuclei align.
Either with field or against field.

Question 3

Larmor Frequency (vL)

Answer 3

Nuclear spin axis in magnetic field.
Spin is called precession - rate of precession gives us a frequency. precession per sec = Larmor frequency.

SEE IMAGE FOR FORMULA
Bo = magnetic field
y = gyromagnetic ratio

Question 4

Quantum model

Answer 4

Different spin states = diff energy when magnetic field applied.
If spin (I) = 1/2 then 2 spin states.
2I + 1 to calculate spin states.

Larmor frequency*planks constant

Question 5

Energies of spin states

Answer 5

H1 gives larger energy gap the C13 when magnetic field applied.

Question 6

NMR machine sample parts

Answer 6

Analyte - sample and solvent
Solvent used - Deuterium to isolate H1 in sample.

Question 7

Inside NMR machine

Answer 7

Superconductive magnetic coil - kept cold by liquid helium, insulated by liquid nitrogen.
Sample hit by em radiation.

Question 8

Different environments

Answer 8

Bare proton has no surrounding electrons so shielding constant is 0
Electron shielding constant is usually positive.
SO Bo (1- shielding constant).

Question 9

Electronegativity and shielding

Answer 9

Less electronegativity near H = less shielding (more deshielding) = shielding constant in smaller, so higher Larmor frequency.