H-NMR Correlations
Molecule 28 |
Group A: Hydrogen atoms in the 7-8 ppm range on the HNMR spectra usually belong to a benzene ring, as holds true with this set of hydrogen atoms. They are fairly deshielded because they are in the meta position on the ring relative to the substituent. |
Group B: This set of hydrogen atoms also are in the 7-8 ppm range, but they are more shielded than those in Hydrogen A because they are in regions of more electron density because they are in the ortho and para positions of the benzene ring (relative to the substituent). |
Group C: This appears at a downshielded value of 5.43 because it is directly attached to a double bonded sp2 carbon. It only 2 three bond neighbors, but because those hydrogens are enantiotopic, they do not show separate splitting patters, and hydrogen C appears as a doublet. The coupling constant is fairly small because the dihedral angle between it and the 3-bond neighbor is relatively small. |
Group D: This hydrogen is extremely close to oxygen, a highly electronegative atom. This results in a downfield chemical shift, and the 2 3 bond neighbors result in the splitting pattern of a triplet. |
Group E: This refers to a set of 2 hydrogens that are located near an electronegative atom, oxygen, which results in the downfield chemical shifts of 4.08-4.14. There may be long-range coupling with other hydrogens, which could be responsible for the splitting pattern as a multiplet. |
Group F: This refers to the three hydrogens on the methyl group are slightly deshielded because the methyl group is directly attached to a double bonded sp2 carbon, which can inductively pull away electron density from the hydrogens. There are no three bond neighbors, which is why the peak appears as a singlet. |
Group G: The chemical shift value is representative of all the hydrogens on the methyl group, which are slightly deshielded because they are next to an OH group, but there are no 3 bond neighbors, because of which the peak appears as a singlet. |
Group H: Similar to the hydrogens from set E, this methyl group is also located in the similar region and close to an OH group, which is why it is slightly deshielded. The oxygen is highly electronegative and can inductively pull electron density towards itself. There are no 3 bond neighbors, so the peak appears as a singlet. |
Group I: The only set of 9 hydrogens that can have the same chemical shift in this molecule belong to the tert-butyl group attached to the silicon; the peak appears as a singlet due to lack of 3 bond neighbors. |
Group J: This set of hydrogens has the lowest chemical shift value of .99 because it is nowhere near any electronegative atoms, and the peak appears as a singlet because there are no 3-bond neighbors. |
Molecule 29 |
Group A: They are on the ‘meta’ positions on the benzene rings (relative to the substituent), which is why the chemical shifts appear in the 7-8 ppm range. The hydrogens on the benzene rings are more deshielded than those from molecule 28 because they are being pulled closer to the oxygen atoms as the spiroketal forms, which results in deshielding through the inductive effect. |
Group B: They are on the ortho and para positions on the benzene rings (relative to the substituent), which is why the chemical shifts appear in the 7-8 ppm range. Similar to hydrogen set A, these hydrogens are relatively deshielded compared to those for 28 due to the oxygens’ inductive effect. |
Group C: Being directly connected to an sp2 carbon with a double bond, this hydrogen becomes deshielded and the chemical shift moves downfield. It has 2 3-bond neighbors, both of which are enantiotopic, which is why the peak appears as a doublet. |
Group D: This set of two hydrogens is located near an electronegative atom, oxygen, which results in the downfield chemical shifts of 4.08-4.14. There may be long-range coupling with other hydrogens, which could be responsible for the splitting pattern as a multiplet. |
Group E: This set of two hydrogens is located near an electronegative atom, oxygen, which results in the downfield chemical shifts of 4.08-4.14. There may be long-range coupling with other hydrogens, which could be responsible for the splitting pattern as a multiplet. |
Group F: This hydrogen is located near bromine, which is highly electronegative and can draw electron density towards itself. The two 3-bond neighbors are diastereotopic, which is why the splitting pattern appears as a doublet of doublets. The hydrogen that is cis to Hydrogen F has a coupling constant of 4.9 Hz, while the trans neighbor has a larger coupling constant of 9.8 Hz. |
Group G: This hydrogen is near many carbon atoms, which results in some deshielding, but not as significant as the result of being near an electronegative atom. There are 2 enantiotopic 3-bond neighbors, which is why the splitting pattern appears as a doublet. The coupling constant, however, is quite large – 17.1 Hz – which is why the hydrogen is being coupled with another hydrogen trans to it. |
Group H: This hydrogen is also surrounded by carbon atoms, which are more electronegative and thus inductively draw electron density away from the hydrogen atom. The atom has 3 3-bond neighbors, of which 2 are enantiotopic; therefore, the splitting pattern is a triplet. |
Group I: This refers to the three hydrogens on the methyl group are slightly deshielded because the methyl group is near an oxygen atom, which can inductively pull away electron density from the hydrogens. There are no three bond neighbors, which is why the peak appears as a singlet. |
| Group J: The chemical shift value is representative of all the hydrogens on the methyl group, which are slightly deshielded because they are near an oxygen atom, but there are no 3 bond neighbors, because of which the peak appears as a singlet. |
| Group K: These hydrogens on the methyl group are also in an area of high electronegative atom density, which can deshield the hydrogen atoms. The chemical shift of these hydrogens is similar to those from set K; there are no 3 bond neighbors. |
| Group L: The only set of 9 hydrogens that can have the same chemical shift in this molecule belong to the tert-butyl group attached to the silicon; the peak appears as a singlet due to lack of 3 bond neighbors. |
Group M: The most shielded set of hydrogens because they are distant from other electronegative atoms and inductive withdrawing effects; there are no 3 bond neighbors, resulting in a single peak. |
Molecule 28
Molecule 29
