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1H and 11Boron NMR assignment

Hey,

I'm in a bit of a pickle assigning some NMRs
The molecule and NMR are attached.

Im confused with what is causing the quartet in the proton NMR for the single hydrogen. Is it coupling to the CH3 protons 5 bonds away?

Also, with the boron nmr, im not sure what the boron is coupling to making that doublet. I think if it was coupling to the nearest hydrogen, there will be 4 peaks due to the 2nI +1 rule (11B has a spin of 3/2)
Proton.png4.0KB
Na%28HB%28pz%27%293%29 NMR spectra.pdf508.6KB
Original post by ALCHYMIST_
Hey,

I'm in a bit of a pickle assigning some NMRs
The molecule and NMR are attached.

Im confused with what is causing the quartet in the proton NMR for the single hydrogen. Is it coupling to the CH3 protons 5 bonds away?

Also, with the boron nmr, im not sure what the boron is coupling to making that doublet. I think if it was coupling to the nearest hydrogen, there will be 4 peaks due to the 2nI +1 rule (11B has a spin of 3/2)


What is the spin of 11B??? Think you'll find it isn't 1/2 so it doesn't split the proton into 2 lines but the four.
Reply 2
Avatar for ALCHYMIST_
ALCHYMIST_
OP
Original post by JMaydom
What is the spin of 11B??? Think you'll find it isn't 1/2 so it doesn't split the proton into 2 lines but the four.


Yep, i already mentioned that the spin of 11B is 3/2 and i am expecting 4 lines if it is coupling to the nearest proton - however in the boron nmr, there are only two broad peaks (correct me if im wrong) so this is where i am confused.
Reply 3
Avatar for illusionz
illusionz
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Original post by ALCHYMIST_
Yep, i already mentioned that the spin of 11B is 3/2 and i am expecting 4 lines if it is coupling to the nearest proton - however in the boron nmr, there are only two broad peaks (correct me if im wrong) so this is where i am confused.


It's the spin of the atom the B is coupling to which matters, because these spins effect the number of possible magnetic environments the B can be in.
Reply 4
Avatar for ALCHYMIST_
ALCHYMIST_
OP
Original post by illusionz
It's the spin of the atom the B is coupling to which matters, because these spins effect the number of possible magnetic environments the B can be in.


Snap, how could i forget..I am such an idiot

Btw, in the proton nmr, if the hydrogen in the H-B bond is coupling to the boron, there are four peaks (as shown) however they are meant to have the same intensities, but in this case, they dont??
Original post by ALCHYMIST_
Snap, how could i forget..I am such an idiot

Btw, in the proton nmr, if the hydrogen in the H-B bond is coupling to the boron, there are four peaks (as shown) however they are meant to have the same intensities, but in this case, they dont??


Sorry, I don't know. Usually couplings aren't resolved to quadrupolar nuclei, so I wouldn't really have expected it to show up at all. (it is usually only resolved for nuclei in highly symmetric environments, Oh and Td)

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