Lecture 11 (NMR, etc.)

Question 1

What does NMR exhibit?

Answer 1

energy absorption leading to transitions between nuclear spin states in nuclei that have a net spin quantum number I different from zero

Question 2

What can make an isotope NMR inactive?

Answer 2

having even mass and atomic numbers have I=0

Question 3

What can make an isotope NMR active?

Answer 3

having odd mass and atomic numbers have fractional I=n/2

Question 4

What is the quantum number when isotopes have even mass number but odd atomic numbers?

Answer 4

I=integer

Question 5

What happens when a nucleus with I=1/2 is placed in a magnetic field?

Answer 5

Its energy levels (degenerate) split depending on the orientation of its spin

Question 6

When the NMR is parallel the energy is …

Answer 6

low

Question 7

When the NMR is antiparallel the energy is …

Answer 7

high

Question 8

What is the formula for the number of spin states using the value of I?

Answer 8

2I+1

Question 9

Energy difference formula?

Answer 9

∆E = (γ∙h∙B)/(2∙π)

Question 10

Resonance frequency formula?

Answer 10

ν = (γ∙B)/(2∙π)

Question 11

What is γ?

Answer 11

It is the gyromagnetic (magnetogyric) ratio, a constant for specific nuclei.

Question 12

What happens when a sample is irradiated with energy, h∙ν = ∆E?

Answer 12

The energy is absorbed and the nucleus is excited; resonance is satisfied.

Question 13

What is Larmor frequency?

Answer 13

a nucleus that has a characteristic for NMR resonance frequency

Question 14

Why is a good portion of nuclei already in an excited state?

Answer 14

There is a small difference between the ground state and the excited state. The excited state and ground state have a small difference in population.

Question 15

Nearly all molecules exist in the higher vibrational state can be excited through absorption of energy. True or false?

Answer 15

False (lower vibrational state)

Question 16

What is saturation?

Answer 16

Upon excitation, the populations can become equal and the absorption of energy cease.

Question 17

How can NMR be increased?

Answer 17

Larger magnets; larger B leads to a larger energy, leading to a larger difference in population between ground and excited state, creating a more intense NMR absorption

Question 18

What is the solution to saturation?

Answer 18

relaxation

Question 19

What is relaxation?

Answer 19

returning the nuclei from an excited state to the ground state

Question 20

What is the effective magnetic field formula?

Answer 20

Beff = B0(1 - σ)

Question 21

What happens to the resolution when there is a larger B makes the resolution