AAMC 9 Biological q's

[Hexon]

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q119on H-NMR for
Br H
| |
:H3C-C-C-CH3
| |
CH3CH3

answer is a singlet, doublet and septet; how is this so? why does the hydrogen give off a septet?

 

[salim271]

The lone hydrogen has two neighbor groups of hydrogens, 6 of them. 1 + 6 neighbors = septet. The singlet is actually the 2 groups of CH3s on the far end, neither have any hydrogen neighbors and read as the same hydrogens so they share a signal. Each of those CH3s that make up the septet hydrogen's neighbors, only have one neighbor, the septet hydrogen, 1 + 1 = doublet for each of those hydrogens.

 

[Hexon]

thanks, salim

H-NMR is always so damn confusing; makes me wonder why they haven't developed better imaging technology for atoms

 

[salim271]

thanks, salim

H-NMR is always so damn confusing; makes me wonder why they haven't developed better imaging technology for atoms

Haha amazingly enough it really is the best way to get a detailed picture of how organic molecules look like without actually seeing them, at least on the MCAT level. Nothing else gives as good of a picture. People who work with NMR for complex molecules probably have computer programs that formulate the most likely structure of the molecule in question by running the NMR data through some software app.

If you keep answering HNMR questions, you'll get used to them. I personally like IR more, its not as accurate in terms of structure but its so much easier to read and formulate a general picture of the functional groups a molecule has with just one glance at it.

 

[axo86]

People who work with NMR for complex molecules probably have computer programs that formulate the most likely structure of the molecule in question by running the NMR data through some software app.

I wish this were true.... 😉 In fact, for complicated molecules we often run 2D NMR experiments, for example, you can plot proton NMR on both the x and y axes of a graph and look for correlations between protons, or you can plot proton NMR on one axis and C13 NMR on the other and look for correlations between protons and carbons. You can use computer calculations to help you find out stuff like the most stable conformation of your molecule, and there are programs to help you process and analyze your spectra, but no automated/magic NMR solver...

 

[salim271]

I wish this were true.... 😉 In fact, for complicated molecules we often run 2D NMR experiments, for example, you can plot proton NMR on both the x and y axes of a graph and look for correlations between protons, or you can plot proton NMR on one axis and C13 NMR on the other and look for correlations between protons and carbons. You can use computer calculations to help you find out stuff like the most stable conformation of your molecule, and there are programs to help you process and analyze your spectra, but no automated/magic NMR solver...

Wow im really surprised there isnt. NMRs get really complex looking once you move past the simple stuff. A computer could handle it easily though, i would think... though im no programmer, but its just a checklist of yes/no if/then either/or... right? 😵 lol

 

[axo86]

When you start looking at more complicated molecules, there becomes an issue where not seeing certain correlations doesn't always mean they aren't there... I'm DEFINITELY not a programmer, but I have a feeling interpreting this kind of logic takes a lot of computing power.

That being said, there are fairly powerful/accurate methods of predicting the NMR structure of a compound, esp C13. But I don't know of any software that does it in reverse!