ChemWiki - User contributions [en]

Mod:Hunt Research Group/Tutorial B

2009-12-15T18:54:29Z

Whn08:

==tutor group notes==

Back to the main [http://www.ch.ic.ac.uk/hunt web-page]

===NMR===
add here a list of points for determining NMR for non-spin 1/2 nuclei with more than one active isotope

If spin = 0. Nothing observed.

Let A be the element symbol for that non-spin 1/2 nuclei

1. Draw the structure of the molecule

2. Determine the geometry of the molecule (e.g. square planar, tetrahedral etc.)

3. Determine the number of magnetically non-equivalent A --> this corresponds to the number of major peaks observed in the spectrum

4. Find out if there is any other spin active nuclei that can couple with A (including the isotopes of A). If so, find out their I (gives information on how the coupling will look), and their natural abundance (gives information on the intensity of peaks).

5. Find out what isotopomers are possible (e.g. B10 H and B11 H), calculate their ratios using natural abundances.

Then, we are ready to start constructing the diagram. Consider each isotopomer individually.

For each of them,

1. If there are n magnetically non-equivalent A, draw out n lines on the spectrum

2. Determine what type of coupling is possible for each magnetically non-equivalent A.

3. Draw tree diagram for coupling, starting first with large coupling, and then small coupling, and so on.

(The splitting of peaks is determined by the 2nI+1 rule. n = no. of different NMR active nuclei connected to the nucleus being observed. The size of coupling constant depends on how strongly the nuclei interact with each other. (coupling deminished as the number of bonds between A and the other nuclei increases, coupling is normally too small to be observed beyond 4 bonds. Besides, the intensity of splitted peaks due to quadrupolar nuclei do not follow the Pascal's triangle.

4. Following the tree diagram, determine the relative intensity of each peak.

Finally, superimpose the spectra for each isotopomer onto one spectra, with intensity weighed according to their natural abundance. This is the spectrum we will observe

Extra note 1: if the nucleus under observation has NMR-active isotopes, then satellites is likely to be observed. The intensities of the satellites depend on the natural abundance of the nucleus.

Mod:Hunt Research Group/Tutorial B

2009-12-10T18:34:19Z

Whn08: /* NMR */

Mod:Hunt Research Group/Tutorial B

2009-12-10T18:32:52Z

Whn08: /* NMR */

User:Whn08

2009-10-10T12:52:19Z

Whn08: Removing all content from page

User:Whn08

2008-12-18T09:50:04Z

Whn08:

<jmol>
<jmolApplet>
<title>Pentahelicene</title>
<color>pink</color>
<size>300</size>
<script>spin on;delay 5;cpk on;delay 5;cpk off;spin off;zoom 160;measure 45 18;</script>
<uploadedFileContents>26314.pdb</uploadedFileContents>
</jmolApplet>
<jmolAppletButton>
<title>Popup molecule</title>
<color>cyan</color>
<uploadedFileContents>26314.pdb</uploadedFileContents>
</jmolAppletButton>
</jmol>

{| border="1"
| napthalene
|}

{| border="1"
|+ A more elaborate example of a table
! Column heading 1 !! Column heading 2 !! Column heading 3
|-
! Row heading 1
| Cell 2 || Cell 3
|-
! Row heading A
|Cell B ||Cell C
|}

<ref name="Blogs">Testing

Example of adding a citation <ref name="Blogs">{{DOI|10.1021/ja9825332}}</ref>
<references />

User:Whn08

2008-12-18T09:39:06Z

Whn08:

User:Whn08

2008-12-18T09:22:47Z

Whn08: New page: <jmol> <jmolApplet> <title>Pentahelicene</title> <color>pink</color> <size>300</size> <script>spin on;delay 5;cpk on;delay 5;cpk off;spin off;zoom 160;measure 45 18;</script> <uploadedFi...

File:26314.pdb

2008-12-18T09:21:28Z

Whn08: