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Author Topic: solving IR  (Read 1725 times)

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Sona

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solving IR
« on: April 07, 2017, 03:26:53 AM »

I have attached a slide here. It containd an IR spectra. I need to deduce the structure.
I have done it in the following way:
Broad 2571-3300 cm-1 for carboxylyc OH
1717cm-1 for carboxylic CO
Hence carboxylic functionality is confirmed.
For the rest, 1265cm-1 is it suggesting CH2Br?
I read that methylene protons ahow a characteristic absorption at about 1465cm-1
So here the peak at 1432cm-1 may indicate methylene.
Thus I am thinking that the structure may be BrCH2CH2CO2H, i.e. 3bromopropanoic acid.
Am I correct?
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Babcock_Hall

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Re: solving IR
« Reply #1 on: April 07, 2017, 04:09:14 AM »

There are others with greater expertise in IR than I have, but bear in mind that there is a C-O single bond in a carboxylic acid to consider.
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Sona

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Re: solving IR
« Reply #2 on: April 07, 2017, 08:50:09 PM »

C-O stretching generally occurs at 1320 - 1210 cm-1, at a medium intensity. Then which one here can be for C-O single bond? 1395 and 1432 cm-1 can they be assigned for C-O? because they are of medium intensity. 1265 is high, 1342 is low in intensity, so I think they are not for C-O.
Then the preoblem is how to know the position of Br in the chain. Is it at the terminal C or at the alpha C? I cannot understand this.
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Sona

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Re: solving IR
« Reply #3 on: April 07, 2017, 08:59:26 PM »

at 1342cm-1 there is a small peak. Is it suggesting characteristic methyle bending? Then the structure should be 2-bromo.
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