[blaisem]

Hello, I have the following practice question of a ¹³C NMR spectrum depicting the carbonyl region of [W(CO)₄[P(OMe)₃](SPh)]^-.  My job is to propose an isomer for it.

I have looked up the following information:

Hydrogen:
Spin = 1/2
Isotopic Abundance = 99.98%
gyromagnetic ratio = 26.8
quadrupole moment = 0

Phosphorous
Spin = 1/2
Isotopic abundance = 100%
gyromagnetic ratio = 10.8
quadrupole moment = 0

Tungsten
Spin = 1/2
Isotopic abundance = 14.4%
gyromagnetic ratio = 1.1
quadrupole moment = 0

Sulfur
Spin = 3/2
Isotopic abundance = 0.76%
gyromagnetic ratio = 2.1
quadrupole moment = 6.78

Oxygen
Spin = 5/2
Isotopic abundance = 0.04%
gyromagnetic ratio = -3.6
quadrupole moment = -2.56

I don't expect the oxygen and sulfur atoms to be visible due to their reduced relaxation times from their quadrupole moment in a non-centrosymmetric molecule.

My best guess so far was that (I drew this into the attached image):

The two left peaks belong to one carbonyl split into a doublet
The two right peaks belong respectively to one carbonyl shifted slightly downfield, and two carbonyls upfield (resulting in the right-most peak's highest integration).  They are each split by some spin 1/2 nucleus.

Phosphorous is a logical assumption for one source of doublet splitting, but the other doublet splitting is clearly from another nucleus due to the different splitting constant.

Tungsten does not seem likely due to its low natural abundance; in fact, I think we can see its effects at 202 and 205 ppm in the two satellite peaks.  Their intensity is so small that carbon-13 coupling at 1% abundance can simply be forgotten.

Hydrogen is presumably too many bonds away; however, it's gyromagnetic constant is around 25, 2.5x as large as phosphorous.  Together, these two nuclei could explain the two different doublet splitting constants.  Is it possible that hydrogen is not too far away?  It would be five bonds though.

Any thoughts or tips in the right direction? Thanks a lot for your time

Edit: I have added a picture of the diagram without my writing on it, if that makes it clearer to look at.  Thanks!

[blaisem]

Alright I have the solution.  See the attached picture.  There are two possible isomers for this complex (maybe I should have posted this in the inorganic forum :/).  The correct isomer is circled.  Only doublet splitting from coupling with phosphorous takes place; the key points are that the carbonyl groups all have different chemical shifts because they are not magnetically equivalent, and that cis-coupling to phosphorous results in a smaller coupling constant than trans-coupling to phosphorous.

The carbonyl group trans to phosphorous has a large splitting because of its 180 degree angle with the phosphorous.
The carbonyl cis to phosphorous and trans to sulphur is less shielded, appearing further downfield.
The remaining two carbonyl grops are equivalent, yielding the right-most doublet.

Thanks to anyone who read and considered the problem.  I hope this helped.