September 29, 2020, 12:25:53 PM
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Topic: Why quartet given in H-1 NMR signal is 1:3:3:1?  (Read 310 times)

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Offline AussieKenDoll

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Why quartet given in H-1 NMR signal is 1:3:3:1?
« on: August 03, 2020, 02:36:52 AM »
why there is two relatively height 1 peaks and two relatively height 3 peaks as of 1:3:3:1?

Offline sjb

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Re: Why quartet given in H-1 NMR signal is 1:3:3:1?
« Reply #1 on: August 03, 2020, 03:31:30 AM »
Each proton splits the signal by ± 1/2. Consider this somewhat analogous to flipping coins, heads or tails. If you flip 3 fair coins, what are the relative frequencies of 3 heads; 2 heads and 1 tail; 1 head and 2 tails; and 3 tails

Offline AussieKenDoll

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Re: Why quartet given in H-1 NMR signal is 1:3:3:1?
« Reply #2 on: August 03, 2020, 04:36:54 AM »
Each proton splits the signal by ± 1/2. Consider this somewhat analogous to flipping coins, heads or tails. If you flip 3 fair coins, what are the relative frequencies of 3 heads; 2 heads and 1 tail; 1 head and 2 tails; and 3 tails
isn't it that 1:3:3:1 proportional to the concentration of the molecule's protons in each distinct chemical environments?

Offline sjb

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Re: Why quartet given in H-1 NMR signal is 1:3:3:1?
« Reply #3 on: August 03, 2020, 05:36:57 AM »
If you mean, for instance electronic environments, then yes. But for instance this is the splitting you'd see for the methylene in methyl ethyl ketone despite there only being two protons. I think you may be confusing to some degree splitting due to coupling and shifts of atoms in general.

Offline Babcock_Hall

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Re: Why quartet given in H-1 NMR signal is 1:3:3:1?
« Reply #4 on: August 03, 2020, 07:29:03 AM »
@OP,

I agree that the intensities provide the relative populations, and it may be applicable to another question that you had about coupling a month or two ago.


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