Anyone Understand Nmr?-- Help

[crest29]

Ok , So
I'm taking this course - its ORG chem Lab II .
we are in the 7th out of 10th week now.
I still have not learned how to interpret
C- NMR and H-NMR data.
I don't know how I've gotten this far because I've had to do several already -- I just guessed on those..
ANyone know how to do this in a simple way and the theory behind it so I don't end up failing the final.. ??
I know its going to be on the final. I can FEEl it.
HELP ME HELP ME!!

=(

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[utpharmdude]

Try this out... http://neon.cm.utexas.edu/academic/courses/Spring2004/CH610B/Iverson/Handouts/NMRhandout2.html
hope it helps...

 

[young skywalker]

You can bet your life it'll be on the final.

You don't really need to understand the theory on why it works.
Just how to interpret it.
You basically can extract 3 pieces of information from it.

1. Depending on how upfield or downfield the peak is, you can guess as to what the functional group is closest to it, basically what kind of environment the carbon or Hydrogen is.

2. By the splitting pattern you can tell how many hydrogens there are connected to each carbon

3. By the coupling values you can tell which hydrogens are associated with each other.

There is no real easy way to do these, just lots of practice. Read your textbook's section and go over practice problems.

 

[PharmD4Me]

For H-NMR:
It deals with electronegativity. The closer a carbon group is to the electronegative atom, the less shielded it is and the farther to the left it will lay. The intensity depends on the number of H's attatched. For every H attached to the carbon atom, the intensity will get larger by the same amount.

For instance:
CH3-CH2-CH2-NO2
~~~~~~~~~~~~~~~~l
~~~~~~~~~l~~~~l~~l
~~~~~~~~~l~~~~l~~l
10_9_8_7_6_5_4_3_2__1__ (ppm)

CH3 is farthest from electro(-) NO2 group so it lies farthest to right and since it has 3 H, its main peak is 3 high on the energy scale.

Blowing up the previous chart you see smaller peaks as well:


_----------------l
_---l------l------l
----ili----,ili,----ili
___5____2____1__(ppm)

Using Pascal's trangle, you can find its neighbors:
@5ppm there are 3 peaks (1:2:1 ratio) so n=1
@2 ppm there are 5 peaks (1:2:3:2:1) so n=2
@1ppm there are 3 peaks (1:2:1) so n=1.

Thats all i ever bothered to learn and it got me through both orgos and labs. Good luck!!!

 

[crest29]

aww thanks guys! i'm going to try to work through some problems this weekend.. hopefully.. after all my partying i guess... =)

 

[DrEaMeRcHiCk]

...ahhh I know how you feel, for my ochem, we just finished mass spec, infrared, and nmr and now we're getting into combined problems... Thanks everyone this thread helped me too =)

 

[DrEaMeRcHiCk]

hey does anyone have any advice for doing nmr?

I'm having problems figuring out the "pieces" like when given the chemical shift, splitting, and integration you use those to figure out the pieces of the structure and put it together.

I've been doing problems but I still can't get it...can anyone help?

 

[aubieRx]

read the textbook.

If you have teh purple book with teh bucky (buckmeinsterfullerene sp....?) ball on the cover ...that book wa s well written