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Topic: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet  (Read 527 times)

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Offline xshadow

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Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« on: October 01, 2020, 08:31:06 AM »

Hi!
I have to answer at this question:

" Explain why the -CH2- group ot the benzyltriphenyl phosphonium salt gives a doublet with H-NMR spectrum"


The -CH2- group don't see any Hydrogen in α position
So that doublet can't be come from a  short range coupling

Can it be a long range coupling because we have some insaturations?
I suppose this:



Thanks

Offline wildfyr

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #1 on: October 01, 2020, 08:42:37 AM »
What is the spin of phosphorous-31?

Offline xshadow

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #2 on: October 01, 2020, 09:16:33 AM »
What is the spin of phosphorous-31?

I think is 1/2

But here we have a H-NMR spectrum...
I think coupling  with other species different from Hydrogen cannot  be seen with the  Hz  for H1[/sup

Is it wrong?

Offline Babcock_Hall

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #3 on: October 01, 2020, 10:05:41 AM »
One is not observing the other nucleus; one is observing coupling to another nucleus.  A good example is the C-13 satellite peaks in the H-1 spectrum.  One of the joys of phosphorus chemistry is seeing beautiful coupling to other nuclei.

Offline xshadow

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #4 on: October 01, 2020, 10:19:20 AM »
One is not observing the other nucleus; one is observing coupling to another nucleus.  A good example is the C-13 satellite peaks in the H-1 spectrum.  One of the joys of phosphorus chemistry is seeing beautiful coupling to other nuclei.

so that doublet arise from  the coupling between the -CH2- and the phosphorus nucleus....

I didn't know this!!
(Usually I've seen 1H NMR spectrum where hydrgen nucleus  is coupled with another hydrogen nucleus ...and I ignored all other type of coupling)


Offline Babcock_Hall

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #5 on: October 01, 2020, 11:15:34 AM »
It would be difficult to decouple the other nuclei; therefore, one usually observes it.  The coupling constants can give useful conformational information.

Offline rolnor

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #6 on: October 01, 2020, 11:38:57 AM »
One is not observing the other nucleus; one is observing coupling to another nucleus.  A good example is the C-13 satellite peaks in the H-1 spectrum.  One of the joys of phosphorus chemistry is seeing beautiful coupling to other nuclei.

I agree, its a nice thing about phosphoros-chemistry! Its great with fluorine-chemistry as well for the same reason.

Offline xshadow

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Re: Benzyltriphenyl phosphonium salt: HNMR -CH2- doublet
« Reply #7 on: October 01, 2020, 04:58:41 PM »
Oh understand
Thanks all!!

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