NMR Spectroscopy
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What does NMR stand for?
Nucleur Magnetic Resonance
What are the nuclei of hydrogen atoms?
electrically charged
What can the nuclei of hydrogen atoms be imagined as?
spinning on their axes
What do spinning charges create?
a magnetic field and act as tiny bar magnets
What will tend to happen if a spinning nucleus is placed in a magnetic field?
it will align itself with the field (c.f. swimming downstream)
In order for a spinning charge to align itself against the field, what does it require?
energy
What kind of energy state is the hydrogen atom in if it aligns itself with the field?
low energy state
What kind of energy state is the hydrogen atom in if it aligns itself against the field?
high energy state
What are protons aligned with the field said to be?
more stable
What kind of energy is supplied to allow transitions to occur?
electromagnetic energy
What does the absoption of energy produce?
NMR signal
What is the position of a signal in an NMR spectrum measured from?
a reference point
What is used as a reference point in an NMR spectrum?
TMS (tetramethyl silane) is added to the sample and the signal from this is taken as zero
What is the signal obtained from any given proton measured in and what is this called?
ppm (parts per million) from TMS and is called chemical shift of the proton
What is a signal obtained for?
all non-equivalent protons
What does each proton in a different environment show?
a different signal
What does the number of signals give clue to?
the number of different protons in the molecule
What is the area under the NMR signal proportional to?
the number of protons which contribute to the signal
What may each signal consist of?
a number of closely packed lines
Why can each signal consist of a number of closely packed lines?
due to the fact that a signal can be split by the neighbouring (adjacent) protons
What is the rule for splitting signals?
n adjacent protons will be split a signal into n+1 peaks