NMR Flashcards
In medicinal chemistry, NMR is used to confirm the identity and purity of drugs. True or false?
True
How is NMR used in formulation science?
For determining aggregation properties of drugs, rates of drug degradation and rates of release of drugs from controlled release systems
How is NMR used in pharmacokinetics?
determination of metabolic products of drugs in urine and plasma
How is NMR used in medical diagnosis?
Imaging of tumours and other abnormalities
All atoms are magnetically active. True or false?
False - to be magnetically active, the atom must have an ODD number of protons and or odd number of neutrons
Nuclei that have a magnetic spin of 0 can be magnetically active. True or false?
False
How many states can a nucleus with a magnetic spin of 0.5 adopt?
Two (aligned against or with magnetic field)
Do the majority of spins align with or against the field and why?
Align with the field, as this requires less energy
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?
True
Does NMR have high or low sensitivity?
low
The sensitivity of NMR is reversibly proportional to the difference in population of high level and low energy. True or false?
False - it is proportional
How is the sensitivity of NMR increased?
Using a bigger magnetic strength (external magnet) or by increasing the amount of sample in the NMR tube
Doubling the magnetic strength reduced the radio frequency by half. True or false?
False - it also doubles the radio frequency
In an NMR experiment, you detect the relaxation back to equilibrium of excited nuclei. True or false?
True
In a Fourier transformation experiment, simultaneous excitation of all nuclei in the sample takes place. What is this due to?
The sample is irradiated with a short pulse of a broad range radiofrequency radiation
Free indcution decay is a plot of signal intensity against time. True or false?
True
Fourier transformation converts the spectrum from units of time to units of frequency. True or false?
True
In NMR, the number of peaks corresponds to the number of equivalent protons. True or false?
False, corresponds to the number of non-equivalent protons
What does the area underneath each signal correspond to?
The number of protons responsible for this signal
What does the shape of the signal depend on?
Whether the proton is exchangeable or non-exchangeable
Can electrons generate their own magnetic field?
Yes - because they have their own charge so circulate around the magnet and can produce their own magnetic field
The magnetic field experienced by the nucleus is increased by local magnetic field induced by electrons. True or false?
False - it is decreased
What is usually used as the reference signal?
Tetramethyl silane (TMS)
Nuclei less shielded than the reference has a negative chemical shift. True or false?
False - have a positive chemical shift
What effect on shielding does an electron donating group attached to the atom have?
Increases shielding and lower resonance frequency
Electronegative groups are “deshielding” and move proton NMR signals from neighbouring protons further “downfield” (higher ppm). True or false?
True
In proton NMR, protons on oxygen and nitrogen have highly variable chemical shifts which are sensitive to temperature, concentration etc. True or false?
True
In proton NMR, the pi system of alkenes, carbonyls and aromatics deshield attached protons and move them to lower ppm. True or false?
False - higher ppm
The same concepts for proton NMR chemical shifts apply to C13 NMR. True or false?
True
Natural abundance of C13 is higher than H1. True or false?
False - H1 is much higher
C13 is more sensitive than H1. True or false?
False - less sensitive
How does a multiplet structure arise?
interaction between neighbouring nuclei (i.e. spin-spin coupling)
What is the unit for magnitude of coupling interactions?
Hertz
The coupling constant, J is independent of the magnetic field strength. True or false?
True
Chemically and magnetically equivalent protons couple to one another. True or false?
False
