¹HNMR Assignments and Descriptions

1. The hydrogen atoms attached to the benzene rings are the farthest downfield and are the most deshielded.


2. Hydrogen atoms B are also attached to a benzene ring but are less deshielded from the electron donating carbon chain.


3. C interacts with the trans D hydrogen, which produces the 15.6 Hz coupling constant.  It is slightly more downfield due to the closer proximity of the ring structure.


4. D couples with C, producing the 15.6 Hz coupling constant.  It has two more coupling constants that result from the deshielded J hydrogen atoms.


5. E couples with the L hydrogen, producing a J constant of 6.8 Hz.  It is attached to a sp3 carbon but is farther downfield due to the presence of the two oxygen atoms that surround the carbon atom.


6. F is diastereotopic to E so it has a similar shift value.  It has a slightly higher coupling constant due to its stereoselective relationship with the L hydrogen.


7. There is a multiplet formed here due to the interactions with the benzene ring hydrogen atoms, A and B.  


8. H couples with Q and R, producing a doublet of doublets.  It has two different coupling constants due to the individual stereoselective relationships with the aforementioned hydrogen atoms.


9. I couples with M to produce a doublet and has a higher J coupling constant due to the ring-like structure and its stereoselectivity.


10. The two J hydrogen atoms couple with D, resulting in a doublet of doublets.  The two coupling constants have differing numbers due to their stereoselective relationship to D.


11. K couples with S, T, O, and P, which results in the quartet of doublets.


12. L couples with the three U hydrogen atoms as well as the M hydrogen atom, which results in a doublet of quartets.  It is slightly farther downfield than M because of the two oxygen atoms that are electron withdrawing groups, and as a result, deshields L.


13. Coupling between M and L, S, and T produces a triplet of doublets.  The J coupling constants are different values because M and L are trans, and S and T have different stereoselective relationships to M.


14. N has a very distinct shift because it does not have any 3-bond neighbors and it is attached to an oxygen atom.


15. O shows up as a quartet of doublets because it couples with Q, R, K, and P.  The highest J constant is from P because it is connected to the same carbon atom but is trans to O.


16. P is a multiplet because its relationship to the surrounding hydrogen atoms is cis, resulting in a muddled group of peaks.


17. Q has a large coupling constant (14.2 Hz) due to its coupling with R.  It also couples with H, O, and P.  It is farther up-field because it is attached to an sp3 carbon atom.


18. R has a very similar shift pattern compared to Q but is slightly more upfield due to its stereoselective relationship with the other hydrogen atoms it is coupled with (Q, H, O, and P).


19. S is attached to an sp3 carbon which accounts for its upfield position.  It has coupling constants due to its relationship with T, H, and M.  Its relationship with T is represented by the 13.2 Hz coupling constant.


20. T is represented as a multiplet due to its stereoselectivity and its multiple interactions with S, H, and M hydrogen atoms.  It has a lower shift because it is attached to an sp3 carbon that is attached to two more sp3 hydrogen carbons.


21. U represents three homotopic hydrogen atoms that interact with the L hydrogen atom, producing the doublet shift.


22. There are no 3-bond neighbors that produce coupling, resulting in a singlet.  Not as high up-field as W or X because carbon is slightly more electronegative than silicon.


23. Silicon acts as a strong electron donating group, making these hydrogen atoms the more shielded and higher up-field.  Also, they have no 3-bond neighbors, making a distinct singlet peak.  This peak is taller than the X-hydrogen atoms’ peak.


24. Silicon acts as a strong electron donating group, making these hydrogen atoms the most shielded and the highest up-field.  Also, they have no 3-bond neighbors, making a distinct singlet peak.

References

"Spin-spin Splitting and Coupling - Coupling in 1H NMR." CU Boulder Organic Chemistry Undergraduate Courses. 2010. Web. 27 Mar. 2011. <http://orgchem.colorado.edu/hndbksupport/nmrtheory/splitting.html>.

"Topicity." Wikipedia, the Free Encyclopedia. Web. 27 Mar. 2011. <http://en.wikipedia.org/wiki/Topicity>.