qeezur
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Some spectroscopic confusions-Help
Hi guys,
I synthesized a novel molecule, I am trying to publish it but i have some confusions in the spectroscopic results, so please help me.
1) If I take CI(-)-MS of Glycerol which has 3 OH sites. Would the molecular ion peak come as [M-3] ... 3 here means 3 protic protons have been
removed. ?
2) in IR, would it be possible for C=O of aromatic esters to peak at around 1695 cm-1 ? ... i know conjugation with aromatic pi nnetwork decreases the
force constant K of C=O but below 1700 is correct ?
3) 3 different C=O groups ( 2 ketones, ester) in one molecule would give 3 peaks or one stronger peak of C=O ?
4) in 1H-NMR, i have two sets of distereotopic protons, each containing 2 geminal H. 2 geminal distereotpic protons of one set are giving their
signals 0.2 ppm away from eachother so they can be written as two signals in data for publishing. The other set of distereopic protons are giving one
larger multiplet so they cant be written separately despite being non equivalent... how do i write this in a publications data ?
I will be very thankful guys !
[Edited on 25-3-2016 by qeezur]
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phlogiston
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Do we get mention in the acknowledgements or a coauthorship for doing your work for you?
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Dr.Bob
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A compound like glycerol would predominantly show up as the M-1 species. Once a molecule has lost a proton, it is harder to remove a second proton.
Also, if you were to remove a second proton, you would change the m/e on top AND bottom, so you would see [M-2]/2 as the peak, or roughly half the
normal MW. Removing three protons on a small molecule is not easy, usually only happens on large proteins.
2) Check Silverstein's table, and look for similar examples, but likely yes. There are computer simulations now that can predict it well. But I
don't have access to them now.
3) IR often has broad peaks, so with 3 carbonyls, you might get one big hump, or two humps, or three peaks, or a large peak with a shoulder. It is
very hard to determine fine details of a novel structure by IR, mostly it is a binary test in the manner of "Does it have any -OH?", Does it have any
C=O groups?, Does it have a nitro group? It is hard to work backwards and say how many and where are they in the molecule. It is VERY good for
confirming a fingerprint of a molecule, ie, is unknown A the same as known B?
4) I would just do something like this 14a: ...3.40 (t, 1H, R-C[B]H1[/B]H2-R'), 3.60 (t, 1H, R-H2-R')... for the first compound/isomer and 14b:
...3.45 - 3.55 ppm (m, 2H, R-CH2-R')... where you call it a multiplet and say which hydrogens they are in the method best for your compound. You
can note in the text, footnote, or supplementary that they are non-equivalent, but not split far enough to measure separately.
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