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Topic: Spectral data to determine isomers  (Read 6205 times)

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Offline Morphic flip

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Spectral data to determine isomers
« on: June 03, 2006, 05:36:09 AM »
Looking at data that would (somehow) tell you what isomer was facial and meridional, the data has 2 peaks for one isomer and 1 peak for the other isomer. How would I tell from the ppm data (chemical shift) was the facial isomer.
The elements are F and P (in PF3) and both have 100% spin I = 1/2
The other group is carbonyl.
So it must be to do with PF3 opposite (meridional) or next to (facial) each other??

I had to do PF3 without subscript 3 as something is blocking it on my PC.

Offline Dan

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Re: Spectral data to determine isomers
« Reply #1 on: June 03, 2006, 08:24:37 AM »
The Ps in the fac isomer are equivalent - each P is cis to 2 Ps, trans to 1 CO and cis to 2 CO. The mer isomer has two inequivalent Ps (trans to each other, cis to 1 P, cis to 3 CO), and one unique (cis to 2 P, trans to 1 CO, cis to 2 CO).
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Offline Morphic flip

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Re: Spectral data to determine isomers
« Reply #2 on: June 03, 2006, 10:04:00 AM »
Thank`s.
If the set of data given showed 2 chemical shifts ( both the same value) for isomer 2 and 3. And another chemical shift for isomer 3, what would be isomer 2, what would be isomer 3?
So isomer 2 has one chemical shift, isomer 3 has 2 chemical shifts.
What would be the fac isomer, isomer 2 or 3?

Offline Dan

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Re: Spectral data to determine isomers
« Reply #3 on: June 03, 2006, 10:28:35 AM »
 
Thank`s.
If the set of data given showed 2 chemical shifts ( both the same value) for isomer 2 and 3. And another chemical shift for isomer 3, what would be isomer 2, what would be isomer 3?
So isomer 2 has one chemical shift, isomer 3 has 2 chemical shifts.
What would be the fac isomer, isomer 2 or 3?
read my post again... How many different chemical shifts would you expect each isomer to have?
My research: Google Scholar and Researchgate

Offline Morphic flip

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Re: Spectral data to determine isomers
« Reply #4 on: June 03, 2006, 11:25:13 AM »
I`m not sure how they match up to what you`ve put.
But guess at 2 for the fac, 3 for the mer?

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Re: Spectral data to determine isomers
« Reply #5 on: June 03, 2006, 11:41:50 AM »
Yes. Nuclei in equivalent environments resonate at the same frequency. So for the fac isomer, all the Ps (and all the Fs, you havent specified wherther it is a 31P or a 19F spectrum, but the appearance will be similar) are in equivalent environments => 1 signal.
In the mer, there are two distinct P (and F) environments => 2 signals.

Additionally, in the fac isomer the PF3s are cis to two COs and trans to one other, and in the mer isomer, one of the PF3s is cis to two COs and trans to one other - this is why you have a coincident signal.
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Offline Morphic flip

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Re: Spectral data to determine isomers
« Reply #6 on: June 05, 2006, 06:14:25 AM »
Thank`s for the well explained reply   :)

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