9/5/24 Flashcards
Spiltting
In the absence of other protons and at the start of a tree diagram, how does the proton appear?
as a singlet
what causes a proton to spilt its signal
the presence of other neighboring protons and their affect on the protons experienced magnetic field
What is the coupling constant
it describes the strength of the nuclei interactions with eachother
if it is large, it means the protons have a larger effect on eachothers magnetic fields
what will we see if the coupling constants are equal?
the n+1 rule will apply and we will see a conjoining of protons to create a large peak
what will we see if the coupling constants are not the same
the n+1 rule will not apply and we will see second order coupling
what is spin spin coupling
it describes the affect that non-equivalent protons on adjacent carbons have on a proton signal. These protons may align or oppose the applied field and can affect the chemical shift of the peak and cause a spiltting affect
When a neighboring proton is in its Beta spin state, how does it affect the main proton?
it causes a spilt in the upfield direction since the magnetic field experienced is lower
when a neighboring proton is in its alpha spin state, how does it affect the main proton
it causes the experienced magnetic field to be higher and causes a spilt in the downfield direction
what is the coupling constant of a cis coupling
10 Hz
what is the coupling constant of trans coupling
15 Hz
what is the coupling constant of geminal coupling
2 Hz
what does a large coupling constant mean
it means there is a better interaction between the magnetic fields of the nuclei
what is the difference that causes a signal to be a doublet of doublets or a triplet
a triplet is seen when the coupling constants are the same, a doublet of doublets is caused by unequal coupling constants
what can experience a proton transfer
a proton connected to a electronegative atom
what is a method of proton transfer
deuterium exchange
what is a deuterium exchange
it allows you to exchange the protons on a electronegative element with deuterium
what happens to the O-H signal when it undergoes a deuterium exchange?
the peak disappears because the NMR only sees protons
if you have an OH group, and a HA nearby, would the OH appear as a neighbor for signal spiltting?
no, the proton transfer occurs so quickly that the NMR does not detect a spiltting so it is ignored at room temperatures
if you wanted to see an OH as a neighbor, what would you have to do to the NMR?
you would need to run the NMR in cool temperatures to slow down the proton exchange
why is a C13 NMR hard to conduct
only 1.1% of carbons are C13, so it is harder to do a C13 NMR and it takes more time and concentrations
