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Topic: Help confused with IR Spectra questions  (Read 5679 times)

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Offline toadesque

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Help confused with IR Spectra questions
« on: December 02, 2009, 02:16:00 PM »
It says:

Match the IR spectra on the next few pages with the names of compounds/structures below. Assign at least two definitive frequency values from each spectrum with relevant structural features.

So I have:

Benzamide



How do I analyze the graphs to tell which one is the Benzamide?

Offline tmartin

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Re: Help confused with IR Spectra questions
« Reply #1 on: December 02, 2009, 02:30:53 PM »
In general, IR is pretty useful to determine if you have a specific functional group in the molecule or not, it's not really the best for piecing together the connectivity (that's why you only need to identify a few key peaks in this case). 

So for your problem...looking at benzamide what are a few key structural features/functional groups that you could use to differentiate it from another molecule?  Specific functional groups will have different peaks in the IR spectrum.  For example, if you were looking for a C-OH (alcohol) in IR, you would hope to see a very broad peak around 3200-3400 (cm^-1).  Then just match up your functional groups with the spectrum that says they are present.

Offline alchmist

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Re: Help confused with IR Spectra questions
« Reply #2 on: December 04, 2009, 12:40:11 AM »
you have a carbonyl group bonded to NH2. the benzene ring also "conjugates" the normal peak you would see at ~1710 for aldehydes and ketones.

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