nmr signals

[tank you]

i know that we should memorize aldehyde (9-10 ppm). but do we have to know the other signals? on some of the kaplan topicals, they ask specifically for aromatic and alkene shifts...

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[Prophecies]

Nothing really...know that an aromatic ring (benzene specifically) will show up between 6-8 ppm...but the REALLY important thing you need to know is how to READ the peaks...signal intensity, spin-spin splitting, things like that. If you can't interpret a basic NMR for ethane or something like that then you are in big trouble...don't worry about knowing what peaks go where...do worry about how to READ the peaks. Good luck to you

 

[SailCrazy]

At my school is was decided that, for the sake of easier scheduling for the Chem department and faculty, they'd drop a day of instruction from Organic, drop the class from 5 to 4 credits, and drop some material from the course...

As a result we completely omitted spin-spin splitting from our NMR interpretations. Is there a quick summary that might help me?

Thanks!

Nothing really...know that an aromatic ring (benzene specifically) will show up between 6-8 ppm...but the REALLY important thing you need to know is how to READ the peaks...signal intensity, spin-spin splitting, things like that. If you can't interpret a basic NMR for ethane or something like that then you are in big trouble...don't worry about knowing what peaks go where...do worry about how to READ the peaks. Good luck to you

 

[Prophecies]

At my school is was decided that, for the sake of easier scheduling for the Chem department and faculty, they'd drop a day of instruction from Organic, drop the class from 5 to 4 credits, and drop some material from the course...

As a result we completely omitted spin-spin splitting from our NMR interpretations. Is there a quick summary that might help me?

Thanks!

From ExamKrackers:

Splitting (called spin-spin splitting) results from neighboring hydrogens that are not chemically equivalent. The number of peaks due to splitting for a group of chemically equivalent hydrogens is given by the simple formula, n+1, where n is the number of neighboring hydrogens that are not chemicall equivalent. A neighboring hydrogen is one that is on an atom adjacent to the atom to which the hydrogen is connected.

It's really hard to understand without seeing diagrams. I recommend looking at this NMR tutorial for more information:

http://chipo.chem.uic.edu/web1/ocol/spec/NMR3.htm

Good luck to you!

 

[Mediculous]

At my school, my professor decided not to teach us any spectroscopy at all during Orgo I. When my Orgo II professor heard about this, he decided he wasn't going to waste his time teaching it either, and said he would give us a break and wouldn't test us on it. How nice of them. 10 pages from Kaplan is all I know about spectroscopy. They seem to emphasize numbers more for IR and theory more for NMR. So far, after two AAMC tests(3R and 4R), I've only seen number-specific questions concerning IR, and the Kaplan material was definitely enough for those. I would memorize IR numbers for alcohols, acids, ketones, and amines.

 

[Prophecies]

At my school, my professor decided not to teach us any spectroscopy at all during Orgo I. When my Orgo II professor heard about this, he decided he wasn't going to waste his time teaching it either, and said he would give us a break and wouldn't test us on it. How nice of them. 10 pages from Kaplan is all I know about spectroscopy. They seem to emphasize numbers more for IR and theory more for NMR. So far, after two AAMC tests(3R and 4R), I've only seen number specific questions concerning IR, and the Kaplan material was definitely enough for those. I would memorize IR numbers for alcohols, acids, ketones, and amines.

You might want to read up on NMR from a source other than Kaplan...NMR is just as important (and just as likely to appear on the MCAT) as IR.

 

[SailCrazy]

Thanks - I think I might have my terminology mixed up. I do understand the n+1 rule with neighboring hydrogens.

What we skipped was something about patterns where, for example, instead of two peaks (one doublet) something in the structure of the molecule causes a doublet of doubltes (two sets of two peaks.) Unfortuantely because we skipped the material, I don't know much more about it than that, so I can't provide a very good explanation.

Thanks for your help, though... At least I know something that will be on there!

From ExamKrackers:

Splitting (called spin-spin splitting) results from neighboring hydrogens that are not chemically equivalent. The number of peaks due to splitting for a group of chemically equivalent hydrogens is given by the simple formula, n+1, where n is the number of neighboring hydrogens that are not chemicall equivalent. A neighboring hydrogen is one that is on an atom adjacent to the atom to which the hydrogen is connected.

It's really hard to understand without seeing diagrams. I recommend looking at this NMR tutorial for more information:

http://chipo.chem.uic.edu/web1/ocol/spec/NMR3.htm

Good luck to you!

 

[Prophecies]

Thanks - I think I might have my terminology mixed up. I do understand the n+1 rule with neighboring hydrogens.

What we skipped was something about patterns where, for example, instead of two peaks (one doublet) something in the structure of the molecule causes a doublet of doubltes (two sets of two peaks.) Unfortuantely because we skipped the material, I don't know much more about it than that, so I can't provide a very good explanation.

Thanks for your help, though... At least I know something that will be on there!

All that doublet of doublet stuff you don't need to know for the MCAT. I know what you are talking about--don't worry about it. The MCAT only tests basic knowledge of NMR and IR skills.

 

[SailCrazy]

All that doublet of doublet stuff you don't need to know for the MCAT. I know what you are talking about--don't worry about it. The MCAT only tests basic knowledge of NMR and IR skills.

Thanks! That's good to know. I'd been wondering about that stuff, but hadn't made it that far down the MCAT study list to check it out.