H NMR - quick help needed

[mosquitoman]

hey guys,

Can someone explain H nmr - specifically how to determine how many peaks there are.



thanks!

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[AZFutureDoc]

Just look at the number of distinct H's. That is really all there is to it?

 

[spyderracing32]

Singlet = hydrogen not spin-coupled to another hydrogen
Doublet = hydrogen spin-coupled to 1 other hydrogen
Triplet = Hydrogen spin-coupled to 2 other hydrogens
etc....

It's very complicated to go into great detail about NMR, but a hydrogen is spin-coupled when it is 3 bonds away from another hydrogen. So think of a molecule CH3-CH. The lone hydrogen is 3 bonds away from 3 other hydrogens which would form a pattern with 4 peaks (a quadruplet). So the quadruplet is produced by the lone hydrogen, but it is indicative of the CH3 group. Each of the CH3 hydrogens is spin coupled to the single CH hydrogen producing a pattern with 2 peaks (a doublet). Again this pattern is produced by the CH3 hydrogen, but it is indicative of the CH hydrogen. The peaks follow a height ratio in accordance to pascals triangle.

 

[CrimsonMirage]

This may seem simplistic but here's my basic understanding of it:

Number of peaks: Each distinct group of hydrogens will produce a peak
Splitting of peaks: The number of smaller peaks each peak splits into will be based on the n+1 rule, where n is the number of hydrogens on the neighboring carbon(s) that are 3 bonds away.
Area under a peak: Basically the integral of a peak will be proportional to the number of hydrogens of that type.

So...CH3-CH2-CH3 would produce two peaks (one for CH3 groups, one for CH2 group). The CH3 peak would be a triplet because there are two hydrogens neighboring. The CH2 peak would be a septet. The ratio of the area under the CH3 peak to that under the CH2 peak would be 3:1.

Hope that answered the question!

 

[spyderracing32]

This may seem simplistic but here's my basic understanding of it:

Number of peaks: Each distinct group of hydrogens will produce a peak
Splitting of peaks: The number of smaller peaks each peak splits into will be based on the n+1 rule, where n is the number of hydrogens on the neighboring carbon(s) that are 3 bonds away.
Area under a peak: Basically the integral of a peak will be proportional to the number of hydrogens of that type.

So...CH3-CH2-CH3 would produce two peaks (one for CH3 groups, one for CH2 group). The CH3 peak would be a triplet because there are two hydrogens neighboring. The CH2 peak would be a septet. The ratio of the area under the CH3 peak to that under the CH2 peak would be 3:1.

Hope that answered the question!

Simplistic but all (and more!) than you'll need to know for the MCAT!