NMR

Question 1

In medicinal chemistry, NMR is used to confirm the identity and purity of drugs. True or false?

Answer 1

True

Question 2

How is NMR used in formulation science?

Answer 2

For determining aggregation properties of drugs, rates of drug degradation and rates of release of drugs from controlled release systems

Question 3

How is NMR used in pharmacokinetics?

Answer 3

determination of metabolic products of drugs in urine and plasma

Question 4

How is NMR used in medical diagnosis?

Answer 4

Imaging of tumours and other abnormalities

Question 5

All atoms are magnetically active. True or false?

Answer 5

False - to be magnetically active, the atom must have an ODD number of protons and or odd number of neutrons

Question 6

Nuclei that have a magnetic spin of 0 can be magnetically active. True or false?

Answer 6

False

Question 7

How many states can a nucleus with a magnetic spin of 0.5 adopt?

Answer 7

Two (aligned against or with magnetic field)

Question 8

Do the majority of spins align with or against the field and why?

Answer 8

Align with the field, as this requires less energy

Question 9

The number of nuclei in the high energy state and the number in the low energy state will differ by an amount determined by Boltzmann distribution. True or false?

Answer 9

True

Question 10

Does NMR have high or low sensitivity?

Answer 10

low

Question 11

The sensitivity of NMR is reversibly proportional to the difference in population of high level and low energy. True or false?

Answer 11

False - it is proportional

Question 12

How is the sensitivity of NMR increased?

Answer 12

Using a bigger magnetic strength (external magnet) or by increasing the amount of sample in the NMR tube

Question 13

Doubling the magnetic strength reduced the radio frequency by half. True or false?

Answer 13

False - it also doubles the radio frequency

Question 14

In an NMR experiment, you detect the relaxation back to equilibrium of excited nuclei. True or false?

Answer 14

True

Question 15

In a Fourier transformation experiment, simultaneous excitation of all nuclei in the sample takes place. What is this due to?

Answer 15

The sample is irradiated with a short pulse of a broad range radiofrequency radiation

Question 16

Free indcution decay is a plot of signal intensity against time. True or false?

Answer 16

True

Question 17

Fourier transformation converts the spectrum from units of time to units of frequency. True or false?

Answer 17

True

Question 18

In NMR, the number of peaks corresponds to the number of equivalent protons. True or false?

Answer 18

False, corresponds to the number of non-equivalent protons

Question 19

What does the area underneath each signal correspond to?

Answer 19

The number of protons responsible for this signal

Question 20

What does the shape of the signal depend on?

Answer 20

Whether the proton is exchangeable or non-exchangeable

Question 21

Can electrons generate their own magnetic field?

Answer 21

Yes - because they have their own charge so circulate around the magnet and can produce their own magnetic field

Question 22

The magnetic field experienced by the nucleus is increased by local magnetic field induced by electrons. True or false?

Answer 22

False - it is decreased

Question 23

What is usually used as the reference signal?

Answer 23

Tetramethyl silane (TMS)

Question 24

Nuclei less shielded than the reference has a negative chemical shift. True or false?

Answer 24

False - have a positive chemical shift

Question 25

What effect on shielding does an electron donating group attached to the atom have?

Answer 25

Increases shielding and lower resonance frequency

Question 26

Electronegative groups are "deshielding" and move proton NMR signals from neighbouring protons further "downfield" (higher ppm). True or false?

Answer 26

True

Question 27

In proton NMR, protons on oxygen and nitrogen have highly variable chemical shifts which are sensitive to temperature, concentration etc. True or false?

Answer 27

True

Question 28

In proton NMR, the pi system of alkenes, carbonyls and aromatics deshield attached protons and move them to lower ppm. True or false?

Answer 28

False - higher ppm

Question 29

The same concepts for proton NMR chemical shifts apply to C13 NMR. True or false?

Answer 29

True

Question 30

Natural abundance of C13 is higher than H1. True or false?

Answer 30

False - H1 is much higher

Question 31

C13 is more sensitive than H1. True or false?

Answer 31

False - less sensitive

Question 32

How does a multiplet structure arise?

Answer 32

interaction between neighbouring nuclei (i.e. spin-spin coupling)

Question 33

What is the unit for magnitude of coupling interactions?

Answer 33

Hertz

Question 34

The coupling constant, J is independent of the magnetic field strength. True or false?

Answer 34

True

Question 35

Chemically and magnetically equivalent protons couple to one another. True or false?

Answer 35

False