IR spectrum, have to memorize chart?

[ipodtouch]

I was wondering how much of the IR chart we had to memorize.

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[MedPR]

I was wondering how much of the IR chart we had to memorize.

Depends which IR chart you are talking about

 

[thestrokes14]

I was wondering how much of the IR chart we had to memorize.

Just know the wavelength absorptions for carbonyl groups, OH groups, and maybe C-H bonds. You really should know these from organic chemistry class, so it shouldn't be much memorization at all. Also know that the right side is the fingerprint region.

 

[chiddler]

yeah. carbonyls, alcohols, aaand amines. and maybe the different SP carbons (SP2,3...)

 

[gettheleadout]

I hope they list the ones you need to know in review books, right? Because I haven't had to memorize any of them for organic thus far...

 

[MedPR]

I hope they list the ones you need to know in review books, right? Because I haven't had to memorize any of them for organic thus far...

If you have TBR It lists all of them, so that probably won't help. I'd say just the common organic stuff like alkyl groups, carbonyl, alcohol, maybe amines.

 

[SaintJude]

Kaplan also identified one key concept in the margins (the key concepts feature rocks) For an absorption to be recorded, the vibration must result in a change in bond dipole moment.

So symmetric stretches don't show up in IR spectra. Most likely this would appear as a pseudo-discrete in a passage asking something like "The triple bond in acetylene is a functional group that does not appear on the spectra. Why?" (obviously more eloquently)

A: Because symmetric stretches involve no net change in dipole moment.

Edit: Just noticed you only wanted to know about the chart, not other concepts. Ignore post above!

So to get to your actual question about the chart. I only memorized the OH and the carbonyl. Looking at trends is most useful to me. MCAT-Review says it best :

Anything around 3000 cm-1 involves a hydrogen atom, be it O-H, N-H, or C-H.
Anything around 2000 cm-1 and below does not involve hydrogen, be it C=O, C=C, C-C, or C-O.

 

[davcro]

Kaplan also identified one key concept in the margins (the key concepts feature rocks) For an absorption to be recorded, the vibration must result in a change in bond dipole moment.

So symmetric stretches don't show up in IR spectra. Most likely this would appear as a pseudo-discrete in a passage asking something like "The triple bond in acetylene is a functional group that does not appear on the spectra. Why?" (obviously more eloquently)

A: Because symmetric stretches involve no net change in dipole moment.

Good to know!

I put all the HNMR, IR, and UV values into a deck of flashcards and memorized them. You can find them here:
http://quizlet.com/8912830/nmr-shifts-davecro-flash-cards/

Maybe this was overkill, but I didn't feel like it took much work to memorize.

 

[411309]

the only ones that have ever come up for me were alcohol and ketone peaks.

 

[gettheleadout]

Good to know!

I put all the HNMR, IR, and UV values into a deck of flashcards and memorized them. You can find them here:
http://quizlet.com/8912830/nmr-shifts-davecro-flash-cards/

Maybe this was overkill, but I didn't feel like it took much work to memorize.

No way am I wasting brain space memorizing all those values.

 

[Godric]

I wondered the same, I read them about twice when I came across them in TBR, and then once I did phase 1 passages the reoccuring ones just were drilled into my head. Know the common ones, -OH, C=O, -NH, Sp2,Sp3. But I am going to make flashcards and when ever i am sitting in class or walking around I'll just review them.

 

[hellocubed]

So symmetric stretches don't show up in IR spectra. Most likely this would appear as a pseudo-discrete in a passage asking something like "The triple bond in acetylene is a functional group that does not appear on the spectra. Why?" (obviously more eloquently)

I am wondering what this means....

Because there are Clearly values for C-C, C=C, and triple bonded carbons as well, all of which are symmetrical.


Edit: Oh nevermind haha

 

[SaintJude]

Well, it's a good question and I guess you figured it out but in case others wonder in the future I'll elaborate.

Symmetrical vibrations of symmetric molecules do not cause absorption of IR radiation. For example, neither of the carbon-carbon bonds in ethene or ethyne absorb IR radiation. Ethene and ethyne are symmetrical molecules. We are not considering the symmetry of just one C-C bond but the symmetry of the entire molecule as a whole.