Proton NMR Spectra

[aspiringdoc09]

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Are we responsible for knowing characteristics of the common chemical shift values? For instance alkyl protons 2-4 ppm, etc? Or, is it out of the scope of the real MCAT? I remember TPRH Orgo indicating that the value is based on if the protons are heavily shielded or not. I can't remember if more shielded has higher ppm? I ask because it seems like most of the recent tests were orgo heavy.

 

[CodeRedDew]

I sincerely doubt that you would have to memorize actual proton shift numbers for the MCAT. Also, the more shielded a proton is, the lower its ppm (ie. a proton near an electronegative atom will have a higher ppm than a proton not near an electronegative atom).

As a sidenote: you SHOULD be familiar with the relative ranges in infrared spectroscopy for groups such as alcohols, carboxylic acids, amines, and carbonyls as I've seen these pop up on some test.

 

[aspiringdoc09]

I sincerely doubt that you would have to memorize actual proton shift numbers for the MCAT. Also, the more shielded a proton is, the lower its ppm (ie. a proton near an electronegative atom will have a higher ppm than a proton not near an electronegative atom).

As a sidenote: you SHOULD be familiar with the relative ranges in infrared spectroscopy for groups such as alcohols, carboxylic acids, amines, and carbonyls as I've seen these pop up on some test.

I was wondering because the free online kaplan test had a chemical shift question and asked about vinylic protons. I wanted to be sure that this type of question won't show up on the real test.

I didn't know I had to know the IR value for amines. Thanks.

 

[N1st]

I sincerely doubt that you would have to memorize actual proton shift numbers for the MCAT. Also, the more shielded a proton is, the lower its ppm (ie. a proton near an electronegative atom will have a higher ppm than a proton not near an electronegative atom).

As a sidenote: you SHOULD be familiar with the relative ranges in infrared spectroscopy for groups such as alcohols, carboxylic acids, amines, and carbonyls as I've seen these pop up on some test.

Also lower ppm =upfield=higher field strength.

 

[CodeRedDew]

I was wondering because the free online kaplan test had a chemical shift question and asked about vinylic protons. I wanted to be sure that this type of question won't show up on the real test.

I didn't know I had to know the IR value for amines. Thanks.

Amines have relatively the same range in infrared spectroscopy as alcohols. The difference is that the amine peaks aren't as deep as the alcohol peaks. Subtle difference that may not be too important, but always good to know 😛