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Topic: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??  (Read 1097 times)

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Offline AussieKenDoll

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P-31 NMR of PF3 , F nuclei equally couple to P, I=1/2 and gives a quartet of 1:3:3:1

But the F-19 NMR of BF3 coupling to the B-11; I=3/2 gives quartet of 1:1:1:1

How do we know if a quartet gives 1:3:3:1 or 1:1:1:1?

Offline Babcock_Hall

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #1 on: July 08, 2020, 10:35:08 AM »
Hi Ken,

When a -CH2 is in-between an oxygen atom and a CH3 group, the methylene group is usually observed to b a 1:3:3:1 quartet.  Do you know about Pascal's triangle and how this relates to coupling?

Offline AussieKenDoll

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #2 on: July 08, 2020, 11:12:53 AM »
yes I know about the pascal triangle and its relation to coupling but how does this 1:1:1:1 comes?

Offline Babcock_Hall

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #3 on: July 08, 2020, 11:19:42 AM »
You stated correctly that a single B-11 nucleus is I = 3/2 (it is one type of quadrupolal nucleus).  What does this actually mean in terms of what spin states the nucleus can be found in?  How is this different from spin-1/2 nuclei?

What can you deduce about the approximate relative populations of the nuclear spin states of B-11?
« Last Edit: July 08, 2020, 11:32:27 AM by Babcock_Hall »

Offline AussieKenDoll

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #4 on: July 08, 2020, 11:31:45 AM »
it can take -3/2,-1/2,1/2,3/2 spin states

Offline Babcock_Hall

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #5 on: July 08, 2020, 11:33:02 AM »
Yes, and the populations of those four states are roughly equal to one another.  For a single spin-1/2 nucleus the populations of the -1/2 and +1/2 are also roughly equal.

Offline AussieKenDoll

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #6 on: July 08, 2020, 11:40:06 AM »
yes they are nearly equal! but how it relates to if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??

Offline Babcock_Hall

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #7 on: July 08, 2020, 11:46:48 AM »
A single F-19 nucleus "feels" whether the B-11 is in the -3/2, -1/2, +1/2, or +3/2 state.  By feeling, I mean that the F-19 experiences a slightly different effective magnetic field.  Because the four states are equally populated, the four F-19 signals are equally intense.  See if you can apply this to the other situation about which you enquired.

Offline Babcock_Hall

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Re: How to determine if a quartet gives 1:3:3:1 or 1:1:1:1 in NMR??
« Reply #8 on: July 09, 2020, 10:48:09 PM »
What does the P-31 nucleus experience?

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